What is electromagnetic wave?

What is electromagnetic wave?
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Very Useful #MustShare With Ur Frnds
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Ans:- We know that energy is transferred from one place to another by means of some kind of medium and the medium is pretty essential as it determines the rate of energy transfer.
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But what happens when there is no medium to transfer energy. How energy can be transferred via vacuum ? The most common example is the sun. Every second huge amount of energy is emitted from the sun which travels in the space and reaches various planets.
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The energy is transferred by electromagnetic waves. Electromagnetic waves are produced by the electric fields and magnetic fields when they oscillate perpendicular to each other.

The light itself is an electromagnetic wave. So, it can be easily said that the speed of electromagnetic wave is the speed of light i.e., 3 × 108 m/s.

electromagnetic wave
Electromagnetic waves are caused by electromagnetic field. Electromagnetic field is that where both electric field and magnetic field are present. When both of these oscillate perpendicularly to each other, electromagnetic wave is generated which can travel through even vacuum. The energy carried by the electromagnetic wave is called radiant energy. In general, now a days electromagnetic waves transmit radio waves, infra-red radiation, gamma Rays.
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The wave length of the waves determine the visibility of these electromagnetic waves i.e. depending on the wavelength some waves are visible to bare eyes and some are invisible, it also determines the colour of the wave.

Star to Delta snd Delta to Star Conversion Techniques......

https://youtu.be/VQMILlnCaBw

All About Electrical Conductors Most Frequent Questions

All About Electrical Conductors Most Frequent Questions

What is Conductor ac Resistance....?
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Ans:- A conductor offers a greater resistance to a flow of alternating current than it does to direct current. This increased resistance is generally expressed as the ac/dc resistance ratio. The two major factors for this increase are the skin effect and the proximity effect of closely spaced current carrying conductors. Other magnetic effects can also cause an additional increase in ac/dc resistance ratios.

What is Electric Fields and Voltage...?
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Ans:- Current flow is charge in motion. We might consider the simple case of a conductor carrying current out to a load and then a return conductor as two separated parallel cylinders of charge. If we neglect conductor diameter line of charge there are electric field lines represented by circles of diameters such that the center of the circles are on the 0 line and each circle passes through the center of the cylinders.

What is Conductor...?
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Ans:- Conductors may be solid or stranded. Metals used are commonly copper or aluminum. An attempt to use sodium was short-lived. The strand can be concentric, compressed,compacted, segmental, or annular to achieve desired properties of  flexibility, diameter, and current density.

What is Circular Mil Sizes...?
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Ans:- Sizes larger than #4/0 AWG are specified in terms of the total cross-sectional area of the conductor and are expressed in circular mils. This method uses an arbitrary area of a conductor that is achieved by squaring the diameter of a solid conductor. This drops the π/4 multiplier required for the actual area of a round conductor.
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A circular mil is a unit of area equal to the area of a circle having a diameter of one mil, one mil equals 0.001
inch. Such a circle has an area of 0.7854 or π/4 square mils. Thus, a wire 10 mils in diameter has a cross-sectional area of 100 circular mils. Likewise, one square inch equals 4/π times 1,000,000=1,273,000 circular mils. For convenience, this is usually expressed in thousands of circular mils and abbreviated kcmil.

What is Non-Shielded Power Cable...?
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Ans:- A cable non-shielded cable may consist of one or several conductors and one or several
insulating layers.
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The cable may contain a jacket. The cable may also include a conductor
shield.
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A cable is not considered fully shielded until both conductor and insulation shields
are present.
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Non-shielded cables are common in the 0 to 5 kV voltage range although
non-shielded power cables through 8 kV have been available.

What is AIR INSULATED CONDUCTORS...?
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Ans:- A metallic conductor suspended from insulating supports, surrounded by air, and carrying electric signals or power may be considered as the simplest case of an insulated conductor.

What is INSULATING TO SAVE SPACE...?
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Ans:- Space is a common constraint that precludes the use of air as an insulator. Imagine the space requirements to wire a house or apartment using bare conductors on supports with air as the insulation. A voltage divider has been created that is made up of the impedance from the conductor to the outside covering surface and another impedance from the covering surface to ground. The distribution of voltage from conductor to the surface of the covering and from the covering surface to ground will be in proportion to these impedances.

What is RISING VOLTAGE...?
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Ans:- Return to the metallic conductor that is covered with an insulating material and suspended in air. When the ground plane is brought close or touches the covering,At low voltages, the effect is negligible. As the voltage increases, the point is reached where the potential gradients are sufficient to cause current to flow across the surface of the covering.

What is Electrical Insulation or Dielectric...?
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Ans:- The insulation dielectric provides sufficient separation between the conductor and the nearest electrical ground to adjacent phase to preclude dielectric failure. For low voltage cables, (2,000 volts and below), the required thickness of insulation to physically protect the conductor is more than adequate

List of All Constants & abbreviation's

What is electrical load?

What is electrical load?

Current flows through a circuit only when it is closed. So, to get a steady flow of current loads are needed to be connected at the terminals of the circuit. Without the load the circuit is said to be open circuited.

If the circuit is completed without connecting the load the circuit is termed to be at short circuited condition the current flow is very huge at the point which can damage the circuit. Load is nothing but impedance.
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There are several types of loads present depending on their nature which are listed below.

According to load nature

Resistive electrical loads
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Capacitive electrical loads
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Inductive electrical loads
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Combination electrical loads

According to load function

Lightning load
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Small appliances load
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Power loads

According to load consumer category

Residential electrical loads
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Commercial electrical loads
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Industrial electrical load
.
Traction loads

According to load grouping

Industrial loads
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Load center

According to load planning

Existing electrical loads
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Future electrical loads
.
New electrical loads

According to load operation time

Continuous electrical loads
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Non- continuous electrical loads
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Duty intermittent electrical loads
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Duty periodic electrical loads
.
Duty short time electrical loads

According to load/phase distribution

Balanced electrical loads
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Non-balanced electrical loads
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Neutral loadsLine to neutral load

According to number of electrical loads phases

Single phase electrical loads
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Three phase electrical loads

According to electrical loads usage method

Fixed place loads
.
Portable loads

According to method of load reduction /control

Dimmed electrical load
.
Shed electrical load
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Shifted electrical load.
.
.
#doshare with Ur frnds

D.C Motors -- MCQ with Answers

D.C Motors -- MCQ with Answers
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1.    No-load speed of which of the following motor will be highest ?
(a)     Shunt motor    
(b)     Series motor
(c)    Cumulative compound motor
(d)    Differentiate compound motor
Ans: b

2.    The direction of rotation of a D.C. series motor can be changed by
(a)     interchanging supply terminals
(b)     interchanging field terminals
(c)    either of (a) and (b) above
(d)    None of the above
Ans: b

3. Which of the following application requires high starting torque ?
(a) Lathe machine
(b) Centrifugal pump
(c) Locomotive
(d) Air blower
Ans: c

4.    If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?
(a)     Series motor
(b)     Shunt motor
(c)    Differentially compound motor
(d)    Cumulative compound motor
Ans: a

5.    Which D.C. motor will be preferred for machine tools ?
(a)    Series motor
(b)    Shunt motor   
(c)    Cumulative compound motor
(d)    Differential compound motor
Ans: b

6.    Differentially compound D.C. motors can find applications requiring
(a)    high starting torque
(b)    low starting torque
(c)     variable speed
(d)    frequent on-off cycles
Ans: b

7.    Which D.C. motor is preferred for elevators ?
(a)    Shunt motor
(b)    Series motor
(c)    Differential compound motor
(d)    Cumulative compound motor
Ans: d

8.    According to Fleming's left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of
(a)     current in the conductor aovtaat of conductor
(c)    resultant force on conductor
(d)    none of the above
Ans: a

9.    If the field of a D.C. shunt motor gets opened while motor is running
(a) the speed of motor will be reduced %
(b) the armature current will reduce
(c)  the motor will attain dangerously high speed 1     
(d) the motor will continue to nuvat constant speed
Ans: c

10.    Starters are used with D.C. motors because
(a)    these motors have high starting torque
(b)    these motors are not self-starting
(c)    back e.m.f. of these motors is zero initially
(d)    to restrict armature current as there is no back e.m.f. while starting
Ans: d

11.    In D.C.  shunt motors as load is reduced
(a)    the speed will increase abruptly
(b)    the speed will increase in proportion to reduction in load
(c)    the speed will remain almost/constant
(d)    the speed will reduce
Ans: c

12.    A D.C. series motor is that which
(a)    has its field winding consisting of thick wire and less turns
(b)    has a poor torque
(c)    can be started easily without load
(d)    has almost constant speed
Ans: a

13.    For starting a D.C. motor a starter is required because
(a)    it limits the speed of the motor
(b)    it limits the starting current to a safe value
(c)    it starts the motor
(d)    none of the above
Ans: b

14.    The type of D.C. motor used for shears and punches is
(a)    shunt motor
(b)    series motor
(c)    differential compoutid D.C. motor
(d)    cumulative compound D.C. motor
Ans: d

15.    If a D.C. motor is connected across the A.C. supply it will
(a)     run at normal speed
(b)     not run
(c)    run at lower speed
(d)    burn due to heat produced in the field winding by .eddy currents
Ans: d

16.    To get the speed of D.C, motor below the normal without wastage of electrical energy is used.
(a)    Ward Leonard control
(b)    rheostatic control
(c)    any of the above method
(d)    none of the above method
Ans: a

17.    When two D.C. series motors are connected in parallel, the resultant speed is
(a)    more than the normal speed
(b)    loss than the normal speed
(c)    normal speed
(d)    zero
Ans: c
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18.    The speed of a D.C. shunt motor more than its full-load speed can be obtained by
(a)    decreasing the field current
(b)    increasing the field current
(c)    decreasing the armature current
(d)    increasing the armature current
Ans: a

19.    In a D.C. shunt motor, speed is
(a)    independent of armature current
(b)    directly  proportional  to  the armature current
(c)    proportional to the square of the current
(d)     inversely proportional to the armature current
Ans: a

20. A direct on line starter is used: for starting motors
(a)    iip to 5 H.P.
(b)    up to 10 H.P.
(c)    up to 15 H.P.
(d)    up to 20 H.P.
Ans: a

21.    What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
(a)    The motor will stop
(b)    The motor will continue to run
(c)    The armature may burn
(d)    The motor will run noisy
Ans: c

22.    In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
(a)    back e.m.f. is equal to armature drop
(b)    armature drop is negligible
(c)    flux is proportional to armature current
(d)    flux is practically constant in D:C. shunt motors
Ans: d

23.    In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
(a)    almost negligible
(b)    rated full-load current
(c)    less than full-load current
(d)    more than full-load current
Ans: d

24.    These days D.C. motors are widely used in
(a)    pumping sets
(b)    air compressors
(c)    electric traction
(d)    machine shops
Ans: c

25.    By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
(a)    Frame
(b)    Shaft
(c)    Commutator
(d)    Stator
Ans: c

26.    In which of the following applications D.C. series motor is invariably tried?
(a)    Starter for a car
(b)    Drive for a water pump
(c)    Fan motor
(d)    Motor operation in A.C. or D.C.
Ans: a

27.    In D.C. machines fractional pitch winding is used
(a)     to improve cooling
(b)     to reduce copper losses
(c)    to increase the generated e.m.f.
(d)    to reduce the sparking
Ans: d

28.    A three point starter is considered suitable for
(a) shunt motors
(b) shunt as well as compound motors
(c) shunt, compound and series motors
(d) all D.C. motors
Ans: b

29.    In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
(a)     100%
(b)     around 90%
(c)    anywhere between 75% and 90%
(d)    less than 50%
Ans: d

30.    The ratio of starting torque to full-load torque is least in case of
(a)    series motors
(b)    shunt motors
(c)    compound motors
(d)    none of the above
Ans: b

32.    In D.C. motor which of the following can sustain the maximum temperature rise?
(a)    Slip rings
(b)    Commutator
(c)    Field winding
(d)    Armature winding
Ans: c

33.    Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
(a)    Lenz's law
(b)    Faraday's law
(c)    Coloumb's law
(d)    Fleming's left-hand rule
Ans: d

34.    Which of the following load normally needs starting torque more than the rated torque?
(a)    Blowers
(b)    Conveyors
(c)    Air compressors
(d)    Centrifugal pumps
Ans: b

35.    The starting resistance of a D.C. motor is generally
(a)    low
(b)    around 500 Q
(c)    1000 Q
(d)    infinitely large
Ans: a

36.    The speed of a D.C. series motor is
(a)    proportional to the armature current
(b)    proportional to the square of the armature current
(c)    proportional to field current
(d)    inversely proportional to the armature current
Ans: d

37.    In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal
to
(a)    100% of the previous value
(b)    50% of the previous value
(c)    25% of the previous value
(d)    10% of the previous value
(e)    none of the above
Ans: c
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38.    The current drawn by the armature of D.C. motor is directly proportional to
(a)    the torque required
(b)    the speed of the motor
(c)    the voltage across the terminals
(d)    none of the above
Ans: a

39.    The power mentioned on the name plate of an electric motor indicates
(a)    the power drawn in kW
(b)    the power drawn in kVA
(c)    the gross power
(d)    the output power available at the shaft
Ans: d

40.    Which D.C. motor has got maximum self loading property?
(a)     Series motor
(b)     Shunt motor
(c)    Cumulatively compounded 'motor
(d)    Differentially compounded motor
Ans: d

41.    Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?
(a)    Series motor
(b)    Shunt motor
(c)    Cumulatively compounded motor
(d)    Differentially compounded motor
Ans: c

42.    If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
(a) nothing will happen to th£ motor
(b) this will make armature to take heavy current, possibly burning it
(c) this will result in excessive speed, possibly destroying armature due  to  excessive centrifugal stresses (d) motor will run at very slow speed
Ans: c

43.    D.C. series motors are used
(a) where load is constant
(b) where load changes frequently
(c) where constant operating speed is needed
(d) in none of the above situations.
Ans: d

44.    For the same H.P. rating and full load speed, following motor has poor starting torque
(a) shunt   
(b) series
(c) differentially compounded
(d) cumulativelyc'ompounded
Ans: c

45.    In case of conductively compensated D.C. series motors, the compensating winding is provided
(a)     as separately wound unit
(6)     in parallel with armature winding
(c)    in series with armature winding
(d)    in parallel with field winding
Ans: c

46.    Sparking at the commutator of a D.C. motor may result in
(a)     damage to commutator segments
(b)     damage to commutator insulation
(c)    increased power consumption
(d)    all of the above
Ans: d

47.    Which of the following motor is preferred for operation in highly explosive atmosphere ?
(a)     Series motor
(b)     Shunt motor
(c)    Air motor
(d)    Battery operated motor
Ans: c

48.    If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
(a)     Starting torque
(b)     Operating speed
(c)    Full-load current
(d)    All of the above
Ans: c

49.    Which one of the following is not the function of pole shoes in a D.C. machine ?
(a)     To reduce eddy current loss
(b)     To support the field coils
(c)    To spread out flux for better unifor-mity
(d)    To reduce the reluctance of the mag-netic path
Ans: a

50.    The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
(a) 4.0   
(b) 2.0
(c) 1.0   
(d) 0.5
Ans: d

51.    The condition for maximum power in case of D.C. motor is
(a)     back e.m.f. = 2 x supply voltage
(b)     back e.m.f. = | x supply voltage
(c)    supply voltage = | x back e.m.f.
(d)    supply voltage = back e.m.f.
Ans: b

52.    For which of the following applications a D.C. motor is preferred over an A.C. motor ?
(a)    Low speed operation
(b)    High speed operation
(c)    Variable speed operation
(d)    Fixed speed operation
Ans: c

53.    In D.C. machines the residual magnetism is of the order of
(a) 2 to 3 per cent
(6) 10 to 15 per cent
(c) 20 to 25 per cent
(d) 50 to 75 per cent
Ans: a

54.    Which D.C. motor is generally preferred for cranes and hoists ?
(a) Series motor    
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor
Ans: a

55.    Three point starter can be used for
(a)    series motor only
(b)    shunt motor only
(c)    compound motor only
(d)    both shunt and compound motor
Ans: d
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Admin :- Bellapuri saikumar
                   ( Sai Saikumar Jn)

D.C. Generators - MCQ and answers

D.C. Generators - MCQ and answers
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1. Laminations of core are generally made of
(a)     case iron
(b)     carbon
(c) silicon steel
(d) stainless steel
Ans: c

2. Which of the following could be lamina-proximately the thickness of lamina-tions of a D.C. machine ?
(a) 0.005 mm
(b) 0.05 mm
(c) 0.5 m
(d) 5 m
Ans: c

3. The armature of D.C. generator is laminated to
(a)     reduce the bulk
(b)     provide the bulk
(c) insulate the core
(d) reduce eddy current loss
Ans: d

4. The resistance of armature winding depends on
(a)     length of conductor
(b)     cross-sectional area of the conductor
(c) number of conductors
(d) all of the above
Ans: d

5. The field coils of D.C. generator are usually made of
(a) mica
(b) copper
(c) cast iron
(d) carbon
Ans: b

6. The commutator segments are connected to the armature conductors by means of
(a) copper lugs    
(b) resistance wires
(c) insulation pads
(d) brazing
Ans: a

7. In a commutator
(a)  copper is harder than mica
(b)  mica and copper are equally hard
(c) mica is harder than copper
(d) none of the above
Ans: c

8. In D.C. generators the pole shoes are fastened to the pole core by
(a) rivets
(b) counter sunk screws
(c) brazing
(d) welding
Ans: b

9. According to Fleming's right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of
(a) motion of conductor
(b) lines of force
(c) either of the above
(d) none of the above
Ans: b

10. Fleming's right-hand rule regarding direction of induced e.m.f., correlates
(a) magnetic flux, direction of current flow and resultant force
(b) magnetic flux, direction of motion and the direction of e.m.f. induced
(c) magnetic field strength, induced voltage and current
(d) magnetic flux, direction of force and direction of motion of conductor
Ans: b

11. While applying Fleming's right-hand rule to And the direction of induced e.m.f., the thumb points towards
(a) direction of induced e.m.f.
(b) direction of flux
(c) direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
(d) direction of motion of conductor, if forefinger points along the lines of flux
Ans: d

12. The bearings used to support the rotor shafts are generally
(a) ball bearings  
(b) bush bearings
(c) magnetic bearmgs
(d) needle bearings
Ans: a

13. In D.C. generators, the cause of rapid brush wear may be
(a) severe sparking
(b) rough commutator surface
(c) imperfect contact
(d) any of the above
Ans: d

14. In lap winding, the number of brushes is always
(a) double the number of poles
(b) same as the number of poles
(c) half the number of poles
(d) two
Ans: b

15. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?
(a) Lap winding  
(b) Wave winding
(c) Either of (a) and (b) above
(d) Depends on other features of design
Ans: b

16. In a four-pole D.C. machine
(a) all the four poles are north poles
(b) alternate poles are north and south
(c) all the four poles are south poles
(d) two north poles follow two south poles
Ans: b

17. Copper brushes in D.C. machine are used
(a) where low voltage and high currents are involved
(b) where high voltage and small cur-rents are involved
(c)  in both of the above cases
(d)  in none of the above cases
Ans: a

18. A separately excited generator as compared to a self-excited generator
(a) is amenable to better voltage con-trol
(b) is more stable
(c) has exciting current independent of load current
(d) has all above features
Ans: d
.

19. In case of D.C. machines, mechanical losses are primary function of
(a) current  
(b) voltage
(c) speed
(d) none of above
Ans: c

20. Iron losses in a D.C. machine are independent of variations in
(a) speed
(b) load
(c) voltage
(d) speed and voltage
Ans: b

21. In D.C. generators, current to the external circuit from armature is given through
(a) commutator    
(b) solid connection
(c) slip rings
(d) none of above
Ans: a

23. Brushes of D.C. machines are made of
(a) carbon
(b) soft copper
(c) hard copper    
(d) all of above
Ans: a

24. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by
(a)Blv
(b)Blv2
(c)Bl2v
(d)Bl2v2
Ans: a

25. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be
(a) 4
(b) 8
(c) 16
(d) 32
Ans: b

26. The material for commutator brushes is generally
(a) mica
(b) copper
(c) cast iron
(d) carbon
Ans: d

27. The insulating material used between the commutator segments is normally
(a) graphite
(b) paper
(c) mica
(d) insulating varnish
Ans: c

28. In D.C. generators, the brushes on commutator remain in contact with conductors which
(a)     lie under south pole
(b)     lie under north pole
(c) lie under interpolar region
(d) are farthest from the poles
Ans: c

29. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
(a)     demagnetisation only
(b)     cross magnetisation as well as magnetisation
(c) crossmagnetisation as well as demagnetising
(d) cross magnetisation only
Ans: c

30. Armature reaction of an unsaturated D.C. machine is
(a) crossmagnetising
(b) demagnetising
(c) magnetising    
(d) none of above
Ans: a

31. D.C. generators are connected to the busbars or disconnected from them only under the floating condition
(a) to avoid sudden loading of the primemover
(b) to avoid mechanicaljerk to the shaft
(c) to avoid burning of switch contacts
(d) all above
Ans: d

32. Eddy currents are induced in the pole shoes of a D.C. machine due to
(a) oscillating magnetic field
(b) pulsating magnetic flux
(c) relative rotation between field and armature
(d) all above
Ans: c

33. In a D.C. machine, short-circuited field coil will result in
(a)    odour of barning insulation
(b)    unbalanced magnetic pull producing vibrations
(c)  reduction of generated voltage for which excitation has to be increased to maintain the voltage
(d)  all above
Ans:

34. Equilizer rings are required in case armature is
(a) wave wound    
(b) lap wound
(c) delta wound    
(d) duplex wound
Ans: b

35. Welding generator will have
(a) lap winding    
(b) wave winding
(c) delta winding
(d) duplex wave winding
Ans: a

36. In case of D.C. machine winding, number of commutator segments is equal to
(a) number of armature coils
(b) number of armature coil sides
(c) number of armature conductors
(d) number of armature turns
Ans: a
.
37. For a D.C. machines laboratory following type of D.C. supply will be suitable
(a)     rotary converter
(b)     mercury are rectifier
(c) induction motor D.C. generator set
(d) synchronous motor D.C. generator set
Ans: c

38. The function of pole shoes in the case of D.C. machine is
(a) to reduce the reluctance of the magnetic path
(b) to spread out the flux to achieve uniform flux density
(c) to support the field coil
(d) to discharge all the above functions
Ans: d

39. In the case of lap winding resultant pitch is
(a) multiplication of front and back pitches
(b) division of front pitch by back pitch
(c) sum of front and back pitches
(d) difference of front and back pitches
Ans: d

40. A D.C. welding generator has
(a) lap winding    
(b) wave moving
(c) duplex winding
(d) any of the above
Ans: a

41. Which of the following statement about D.C. generators is false ?
(a)     Compensating winding in a D.C. machine helps in commutation
(b)     In a D. C. generator interpoles winding is connected in series with the armature winding
(c)  Back pitch and front pitch are both odd and approximately equal to the pole pitch
(d)  Equilizing bus bars are used with parallel running of D.C. shunt generators
Ans: d

42. The demagnetising component of armature reaction in a D.C. generator
(a) reduces generator e.m.f.
(b) increases armature speed
(c) reduces interpoles flux density
(d) results in sparking trouble
Ans: a

43. Magnetic field in a D.C. generator is produced by
(a) electromagnets
(b) permanent magnets
(c) both (a) and (b)
(d) none of the above
Ans: a

44. The number of brushes in a commutator depends on
(a)     speed of armature
(b)     type of winding
(c)  voltage
(d)  amount of current to be collected
Ans: d

45. Compensating windings are used in D.C. generators
(a)     mainly to reduce the eddy currents by providing local short-circuits
(b)     to provide path for the circulation of cooling air
(c) to neutralise the cross-magnetising effect of the armature reaction
(d) none of the above
Ans: c

46. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ?
(a) Dummy coils  
(b) Commutator
(c) Eye bolt
(d) Equilizer rings
Ans: b

47. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
(a)     using conductor of annealed copper
(b)  using commutator with large number of segments
(c)  using carbon brushes of superior quality
(d)  using equiliser rings
Ans: c

48. In D.C. generators, lap winding is used for
(a) high voltage, high current
(b) low voltage, high current
(c) high voltage, low current
(d) low voltage, low current
Ans: b

49. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be
(a) 2 : 3
(b) 3 : 1
(c) 3 : 2
(d) 1 : 3
Ans: b

50. The voltage drop for which of the following types of brush can be expected to be least ?
(a) Graphite brushes
(b) Carbon brushes
(c) Metal graphite brushes
(d) None of the above
Ans: c

51. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be
(a) E/2
(b) 2E
(c) slightly less than E
(d) E
Ans: b

52. In a D.C. generator the actual flux distribution depends upon
(a) size of air gap
(b) shape of the pole shoe
(c) clearance between tips of the ad¬jacent pole shoes
(d) all of the above
Ans:

53. The armature core of a D.C. generator is usually made of
(a)     silicon steel    
(b)     copper
(c) non-ferrous material
(d) cast-iron
Ans: a

.
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-- Admin :- Bellapuri saikumar
                      ( Sai Saikumar Jn)

A.C. Fundamentals, Circuits and Circuit Theory - MCQ with Answers

A.C. Fundamentals, Circuits and Circuit Theory - MCQ with Answers

1. A sine wave has a frequency of 50 Hz. Its angular frequency is _______ radian/second.
(a) 100 n
(b) 50 jt
(c) 25 jt
(d) 5 n
Ans: a

2. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 20 Q. If frequency is increased to 100 Hz, reactance becomes_____ohms.
(a) 2.5
(b) 5
(c) 10
(d) 15
Ans: c
3. The period of a wave is
(a)    the same as frequency
(6)    time required to complete one cycle
(c) expressed in amperes
(d) none of the above
Ans: b
4. The form factor is the ratio of
(a)    peak value to r.m.s. value
(6)    r.m.s. value to average value
(c) average value to r.m.s. value
(d) none of the above
Ans: b
5. The period of a sine wave is _____ seconds.
Its frequency is
(a) 20 Hz
(b) 30 Hz
(c) 40 Hz
(d) 50 Hz
Ans: d
6. A heater is rated as 230 V, 10 kW, A.C. The value 230 V refers to
(a)  average voltage
(b)  r.m.s. voltage  
(c)     peak voltage
(d)  none of the above
Ans: b

7. If two sinusoids of the same frequency but of different amplitudes and phase angles are subtracted, the resultant is
(a) a sinusoid of the same frequency
(b) a sinusoid of half the original frequency
(c) a sinusoid of double the frequency
(d) not a sinusoid
Ans: a

8.   The peak value of a sine wave is 200 V. Its average value is
(a) 127.4 V
(b) 141.4 V
(c) 282.8 V
(d)200V
Ans: a

9. If two sine waves of the same frequency have a phase difference of JT radians, then
(a) both will reach their minimum values at the same instant
(b) both will reach their maximum values at the same instant
(c) when one wave reaches its maximum value, the other will reach its minimum value
(d) none of the above
Ans: c

10. The voltage of domestic supply is 220V. This figure represents
(a) mean value    
(b) r.m.s. value
(c) peak value
(d) average value
Ans: a

11. Two waves of the same frequency have opposite phase when the phase angle between them is
(a) 360°
(b) 180°
(c) 90°
(d) 0°
Ans: b

12. The power consumed in a circuit element will be least when the phase difference between the current and
voltage is
(a) 180"
(b) 90°
(c) 60°
(d) 0°
Ans: b

13. The r.m.s. value and mean value is the same in the case of
(a) triangular wave
(6) sine wave
(c) square wave
(d) half wave rectified sine wave
Ans: c

14. For the same peak value which of the following wave will 'have the highest r.m.s. value ?
(a) square wave
(b) half wave rectified sine wave
(c) triangular wave
(d) sine wave
Ans: a

15. For the same peak value, which of the following wave has the least mean value ?
(a) half wave rectified sine wave
(b) triangular wave
(c) sine wave
(d) square wave
Ans: a

16. For a sine wave with peak value Imax the r.m.s. value is
(a) 0.5 Imax
(b) 0.707
(c) 0.9
(d) 1.414 Lmax
Ans: b

17. Form Factor is the ratio of
(a) average value/r.m.s. value
(b) average value/peak value
(e) r.m.s. value/average value
(d) r.m.s. value/peak value
Ans: c

18. Form factor for a sine wave is
(a) 1.414
(b) 0.707
(c) 1.11
(d) 0.637
Ans: c

.
19. For a sine wave with peak value Emax______8.30. the average value is
(a) 0.636 Emax
(b) 0.707 Emax
(c) 0.434 EWc
(d) lAUEmax
Ans: a

20. For a frequency of 200 Hz, the time period will be
(a) 0.05 s
(b) 0.005 s
(c) 0.0005 s
(d) 0.5 s
Ans: b

21. The phase difference between voltage and current wave through a circuit element is given as 30°. The essential condition is that
(a) both waves must have same frequency
(b) both   waves  must  have identical peak values
(c) both waves must have zero value at the same time
(d) none of the above
Ans: a

22. The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of______degrees.
(a) 90
(b) 60
(c) 45
(d) 30
Ans: c

23. Capacitive reactance is more when
(a)     capacitance is less and frequency of supply is less
(b)     capacitance is less and frequency of supply is more
(c) capacitance is more and frequency of supply is less
(d) capacitance is more and frequency of supply is more
Ans: a

24. In a series resonant circuit, the impedance of the circuit is
(a) minimum
(b) maximum
(c) zero
(d) none of the above
Ans: a

25. Power factor of an electrical circuit is equal to
(a) R/Z
(b) cosine of phase angle difference between current and voltage
(c) kW/kVA
(d) ratio of useful current to total current Iw/I
(e) all above
Ans: e

26. The best place to install a capacitor is
(a) very near to inductive load
(b) across the terminals of the inductive load
(c) far away from the inductive load
(d) any where
Ans: b

27. Poor power factor
(a)     reduces load handling capability of electrical system
(b)     results in more power losses in the electrical system
(c)  overloads alternators, transformers and distribution lines
(d)  results in more voltage drop in the line
(e)  results in all above
Ans: e

28. Capacitors for power factor correction are rated in
(a) kW
(b) kVA
(c) kV
(d) kVAR
Ans: d

29. In series resonant circuit, increasing inductance to its twice value and reducing capacitance to its half value
(a) will change the maximum value of current at resonance
(6) will change the resonance frequency
(c) will change the impedance at resonance frequency
(d) will increase the selectivity of the circuit
Ans: d

30. Pure inductive circuit
(a) consumes some power on average
(b) does not take power at all from a line
(c) takes power from the line during some part of the cycle and then returns back to it during other part of the cycle
(d) none of the above
Ans: c

31. Inductance affects the direct current flow
(a) only at the time of turning off
(b) only at the time of turning on
(c) at the time of turning on and off
(d) at all the time of operation
Ans: c

32. Inductance of a coil Varies
(a)     directly as the cross-sectional area of magnetic core
(b)     directly  as  square  of number of turns
(c) directly as the permeability of the core
(d) inversely as the length of the iron path
(e) as (a) to (d)
Ans: e

33. All the rules and laws of D.C. circuit also apply to A.C. circuit containing
(a) capacitance only
(b) inductance only
(c) resistance only
(d) all above
Ans: c

34. Time constant of an inductive circuit
(a) increases with increase of inductance and decrease of resistance
(b) increases with the increase of inductance and the increase of resistance
(c) increases with decrease of inductance and decrease of resistance
(d) increases with decrease of inductance and increase of resistance
Ans: a

35. Power factor of an inductive circuit is usually improved by connecting capacitor to it in
(a) parallel
(b) series
(c) either (a) or (b)
(d) none of the above
Ans: a

36. In a highly capacitive circuit the
(a) apparent power is equal to the actual power
(b) reactive power is more than the apparent power
(c) reactive power is more than the actual powetf
(d) actual power is more than its reactive power
Ans: c
.
.

37. Power factor of the following circuit will be zero
(a) resistance
(b) inductance
(c) capacitance      
(d) both (b) and (c)
Ans: d

38. Power factor of the following circuit will be unity
(a) inductance
(b) capacitance
(c) resistance
(d) both (a) and (b)
Ans: c

39. Power factor of the system is kept high
(a) to reduce line losses
(b) to maximise the utilization of the capacities of generators, lines and transformers
(c) to reduce voltage regulation of the line
(d) due to all above reasons
Ans: d

40. The time constant of the capacitance circuit is defined as the time during which voltage
(a) falls to  36.8% of its final steady value
(b) rises to 38.6% of its final steady value
(c) rises to 63.2% of its final steady value
(d) none of the above
Ans: c

41. In a loss-free R-L-C circuit the transient current is
(a) oscillating
(b) square wave
(c) sinusoidal
(d) non-oscillating
Ans: c

42. The r.m.s. value of alternating current is given by steady (D.C.) current which when flowing through a given circuit for a given time produces
(a) the more heat than produced by A.C. when flowing through the same circuit
(b) the same heat as produced by A.C. when flowing through the same circuit
(c) the less heat than produced by A.C. flowing through the same circuit
(d) none of the above
Ans: b

43. The square waveform of current has following relation between r.m.s. value and average value.
(a) r.m.s. value is equal to average value
(b) r.m.s. value of current is greater than average value
(c) r.m.s. value of current is less than average value
(d) none of the above
Ans: a

44. The double energy transient occur in the
(a) purely inductive circuit
(b) R-L circuit
(c) R-C circuit
(d)     R-L-C circuit
Ans: d

45. The transient currents are associated with the
(a) changes in the stored energy in the inductors and capacitors
(b) impedance of the circuit
(c) applied voltage to the circuit
(d) resistance of the circuit
Ans: a

46. The power factor at resonance in R-L- C parallel circuit is
(a) zero
(b) 0.08 lagging
(c) 0.8 leading
(d) unity
Ans: d

47. In the case of an unsymmetrical alternating current the average value must always be taken over
(a) unsymmetrical part of the wave form
(b) the quarter cycle
(c) the half cycle
(d) the whole cycle
Ans: d

48. In a pure resistive circuit
(a) current lags behind the voltage by 90°
(b) current leads the voltage by 90°
(c) current can lead or lag the voltage by 90°
(d)     current is in phase with the voltage
Ans: d

49. In a pure inductive circuit
(a) the current is in phase with the voltage
(b) the current lags behind the voltage by 90°
(c) the current leads the voltage by 90°
(d) the current can lead or lag by 90°
Ans: b

50. In a circuit containing R, L and C, power loss can take place in
(a) C only
(b) L only
(c) R only
(d) all above
Ans: c

51. Inductance of coil
(a) is unaffected by the supply frequency
(b) decreases with the increase in supply frequency
(c) increases with the increase in supply frequency
(d) becomes zero with the increase in supply frequency
Ans: c

52. In any A.C. circuit always
(a) apparent power is more than actual power
(b) reactive power is more than apparent power
(c) actual power is more than reactive power
(d) reactive power is more than actual power
Ans: a

53. Which of the following circuit component opposes the change in the circuit voltage ?
(a) Inductance      
(b) Capacitance
(c) Conductance    
(d) Resistance
Ans:

54. In a purely inductive circuit
(a) actual power is zero
(b) reactive power is zero
(c) apparent power is zero
(d) none of above is zero
Ans: a

55. Power factor of electric bulb is
(a) zero
(b) lagging
(c) leading
(d) unity
Ans: d

56. Pure inductive circuit takes power from the A.C. line when
(a) applied voltage decreases but cur¬rent increases
(b) applied voltage increases but cur¬rent decreases
(c) both applied voltage and current increase
(d) both applied voltage and current decrease
Ans: a
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Admin:- Bellapuri saikumar
                 ( sai saikumar jn)

Electromagnetic Induction - MCQ and answers

Electromagnetic Induction - MCQ and answers

1. The property of coil by which a counter e.m.f. is induced in it when the current through the coil changes is known as
(a)     self-inductance
(b)     mutual inductance
(c)     series aiding inductance
(d)     capacitance
Ans: a

2. As per Faraday's laws of electromagnetic induction, an e.m.f. is induced in a conductor whenever it
(a) lies perpendicular to the magnetic flux
(b) lies in a magnetic field
(e) cuts magnetic flux
(d) moves parallel to the direction of the magnetic field
Ans: c

3. Which of the following circuit element stores energy in the electromagnetic field ?
(a) Inductance      
(b) Condenser
(c) Variable resistor
(d) Resistance
Ans: a

4. The inductance of a coil will increase under all the following conditions except
(a) when more length for the same number of turns is provided
(6) when the number of turns of the coil increase
(c) when more area for each turn is provided
(d) when permeability of the core increases
Ans: a

5. Higher the self-inductance of a coil,
(a) lesser its weber-turns
(b) lower the e.m.f. induced
(c) greater the flux produced by it
(d) longer the delay in establishing steady current through it
Ans: d

6. In an iron cored coil the iron core is removed so that the coil becomes an air cored coil. The inductance of the coil will
(a) increase
(b) decrease
(c) remain the same
(d) initially increase and then decrease
Ans: b

7. An open coil has
(a) zero resistance and inductance
(b) infinite resistance and zero inductance
(c) infinite resistance and normal inductance
(d) zero resistance and high inductance
Ans: b

8. Both the number of turns and the core length of an inductive coil are doubled.
Its self-inductance will be
(a) unaffected
(b) doubled
(c) halved
(d) quadrupled
Ans: b

9. If current in a conductor increases then according to Lenz's law self-induced voltage will
(a) aid the increasing current
(b) tend to decrease the amount of cur-rent
(c) produce current opposite to the in-creasing current
(d) aid the applied voltage
Ans: c

10. The direction of incViced e.m.f. can be found by
(a) Laplace's law  
(b) Lenz's law
(c) Fleming's right hand rule
(d) Kirchhoff s voltage law
Ans: b

11. Air-core coils are practically free from
(a) hysteresis losses
(b) eddy current losses
(c) both (a) and (b)
(d) none of the above
Ans: c

12. The magnitude of the induced e.m.f. in a conductor depends on the
(a) flux density of the magnetic field
(b) amount of flux cut
(c) amount of flux linkages
(d) rate of change of flux-linkages
Ans: d

13. Mutually inductance between two magnetically-coupled coils depends on
(a) permeability of the core
(b) the number of their turns
(c) cross-sectional area of their com-mon core
(d) all of the above
Ans: d

14. A laminated  iron core has  reduced eddy-current losses because
(a) more wire can be used with less D.C. resistance in coil
(b) the laminations are insulated from each other
(c) the magnetic flux is concentrated in the air gap of the core
(d) the laminations are stacked vertf-cally
Ans: b

15. The law that the induced e.m.f. and current always oppose the cause producing them is due to
(a) Faraday
(b) Lenz
(c) Newton
(d) Coulomb
Ans: b

16. Which of the following is not a unit of inductance ?
(a) Henry
(b) Coulomb/volt ampere
(c) Volt second per ampere
(d) All of the above
Ans: b

17. In case of an inductance, current is proportional to
(a) voltage across the inductance
(b) magnetic field
(c) both (a) and (b)
(d) neither (a) nor (b)
Ans: b

18. Which of the following circuit elements will oppose the change in circuit current ?
(a) Capacitance    
(b) Inductance
(c) Resistance
(d) All of the above
Ans: b
.
19. For a purely inductive circuit which of the following is true ?
(a) Apparent power is zero
(b) Relative power is.zero
(c) Actual power of the circuit is zero
(d) Any capacitance even if present in the circuit will not be charged
Ans: c

20. Which of the following is unit of inductance ?
(a) Ohm
(b) Henry
(c) Ampere turns  
(d) Webers/metre
Ans: b

21. An e.m.f. of 16 volts is induced in a coil of inductance 4H. The rate of change of current must be
(a) 64 A/s
(b) 32 A/s
(c) 16 A/s
(d) 4 A/s
Ans: d

22. The core of a coil has a length of 200 mm. The inductance of coil is 6 mH. If the core length is doubled, all other quantities, remaining the same, the in ductance will be
(a) 3 mH
(b) 12 mH
(c) 24mH
(d)48mH
Ans: a

23. The self inductances of two coils are 8 mH and 18 mH. If the co-efficients of coupling is 0.5, the mutual inductance of the coils is
(a) 4 mH
(b) 5 mH
(c) 6 mH
(d) 12 mH
Ans: c

24. Two coils have inductances of 8 mH and 18 mH and a co-efficient of coupling of 0.5. If the two coils are connected in series aiding, the total inductance will be
(a) 32 mH
(b) 38 mH
(c) 40 mH
(d) 48 mH
Ans: b

25. A 200 turn coil has an inductance of 12 mH. If the number of turns is increased to 400 turns, all other quantities (area, length etc.) remaining the same, the inductance will be
(a) 6 mH
(b) 14 mH
(c) 24 mH
(d) 48 mH
Ans: d

26. Two coils have self-inductances of 10 H and 2 H, the mutual inductance being zero. If the two coils are connected in series, the total inductance will be
(a) 6 H
(b) 8 H
(c) 12 H
(d) 24 H
Ans: c

27. In case all the flux from the current in coil 1 links with coil 2, the co-efficient of coupling will be
(a) 2.0
(b) 1.0
(c) 0.5
(d) zero
Ans: b

28. A coil with negligible resistance has 50V across it with 10 mA. The inductive reactance is
(a) 50 ohms
(b) 500 ohms
(c) 1000 ohms
(d) 5000 ohms
Ans: d

29. A conductor 2 metres long moves at right angles to a magnetic field of flux density 1 tesla with a velocity of 12.5 m/s. The induced e.m.f. in the conductor will be
(a) 10 V
(6) 15 V
(c) 25V
(d) 50V
Ans: c

30. Lenz's law is a consequence of the law of conservation of
(a) induced current
(b) charge
(c) energy
(d) induced e.m.f.
Ans: c

31. A conductor carries 125 amperes of current under 60° to a magnetic field of 1.1 tesla. The force on the conductor will be
nearly
(a) 50 N
(b) 120 N
(c) 240 N
(d) 480 N
Ans: b

32. Find the force acting on a conductor 3m long carrying a current of 50 amperes at right angles to a magnetic field having a flux density of 0.67 tesla.
(a) 100 N
(b) 400 N
(c) 600 N
(d) 1000 N
Ans: a

33. The co-efficient of coupling between two air core coils depends on
(a) self-inductance of two coils only
(b) mutual inductance between two coils only
(c) mutual inductance and self inductance of two coils
(d) none of the above
Ans: c

34. An average voltage of 10 V is induced in a 250 turns solenoid as a result of a change in flux which occurs in 0.5 second. The total flux change is
(a) 20 Wb
(b) 2 Wb
(c) 0.2 Wb
(d) 0.02 Wb
Ans: d

35. A 500 turns solenoid develops an average induced voltage of 60 V. Over what time interval must a flux change of 0.06 Wb occur to produce such a voltage ?
(a) 0.01 s
(b) 0.1 s
(c) 0.5 s
(d) 5 s
Ans: c

36. Which of the fpllowing inductor will have the least eddy current losses ?
(a) Air core
(b) Laminated iron core
(c) Iron core
(d) Powdered iron core
Ans: a

37. A coil induces 350 mV when the current changes at the rate of 1 A/s. The value of inductance is
(a) 3500 mH
(b) 350 mH
(c) 250 mH
(d) 150 mH
Ans: b
.

Admin :- Bellapuri saikumar
                  ( Sai Saikumar Jn)

Magnetic Circuit - electrical MCQ and answers

Magnetic Circuit - electrical MCQ and answers

1. An air gap is usually inserted in magnetic circuits to
(a)     increase m.m.f.
(b)     increase the flux
(c) prevent saturation
(d) none of the above
Ans: c

2. The relative permeability of a ferromagnetic material is
(a)     less than one    
(b)     more than one
(c) more than 10
(d) more than 100 or 1000
Ans: d

3. The unit of magnetic flux is
(a)     henry
(b)     weber
(c) ampereturn/weber
(d) ampere/metre
Ans: b

4. Permeability in a magnetic circuit corresponds to______ in an electric circuit.
(a) resistance
(b) resistivity
(c) conductivity    
(d) conductance
Ans: c

5. Point out the wrong statement.
Magnetic leakage is undesirable in electric machines because it
(a) lowers their power efficiency
(b) increases their cost of manufacture
(c) leads to their increased weight
(d) produces fringing
Ans: a

6. Relative permeability of vacuum is
(a) 1
(b) 1 H/m
(c) 1/4JI
(d) 4n x 10-' H/m
Ans: a

7. Permanent magnets are normally made of
(a) alnico alloys    
(b) aluminium
(c) cast iron
(d) wrought iron
Ans: a

8. Energy stored by a coil is doubled when its current is increased by percent.
(a) 25
(b) 50
(c)41.4
(d) 100
Ans: c

9. Those magnetic materials are best suited for making armature and transformer cores which have____permeability and_______hystersis loss.
(a) high, high
(b) low, high
(c) high, low
(d) low, low
Ans: c

10. The rate of rise of current through an inductive coil is maximum
(a)     at 63.2% of its maximum steady value
(b)     at the start of the current flow
(c) after one time constant
(d) near the final maximum value of current
Ans: b

11. When both the inductance and resistance of a coil are doubled the value of
(a) time constant remains unchanged
(b) initial  rate  of rise  of current is doubled
(c) final steady current is doubled
(d) time constant is halved
Ans: a

12. The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V is_______Vs
(a) 50
(b) 20
(c) 0.05
(d) 500
Ans: b

13. A material for good magnetic memory should have
(a) low hysteresis loss
(b) high permeability
(c) low retentivity
(d) high retentivity
Ans: d

14. Conductivity is analogous to
(a) retentivity
(b) resistivity
(c) permeability    
(d) inductance
Ans: c

15. In a magnetic material hysteresis loss takes place primarily due to
(a) rapid reversals of its magnetisation
(b) flux density lagging behind magnetising force
(c) molecular friction
(d) it high retentivity
Ans: d

16. Those materials are well suited for making permanent magnets which have______retentivity and _______coercivity.
(a) low, high
(b) high, high
(c) high, low
(d) low, low
Ans: b

17. If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be
(a) zero
(b) small
(c) large
(d) none of the above
Ans: c

18. Hard steel is suitable for making permanent magnets because
(a) it has good residual magnetism
(b) its hysteresis loop has large area
(c) its mechanical strength is high
(d) its mechanical strength is low
Ans: a

19. Silicon steel is used in electrical machines because it has
(a)     low co-ercivity
(b)     low retentivity
(c) low hysteresis loss
(d) high co-ercivity
Ans: c

20. Conductance is analogous to
(a) permeance
(b) reluctance
(c) flux
(d) inductance
Ans: a

21. The property of a material which opposes the creation of magnetic flux in it is known as
(a) reluctivity
(b) magnetomotive force
(c) permeance
(d)     reluctance
Ans: d

22. The unit of retentivity is
(a)     weber
(b)     weber/sq. m
(c) ampere turn/metre
(d) ampere turn
Ans: b

23. Reciprocal of reluctance is
(a) reluctivity
(b) permeance
(c) permeability    
(d) susceptibility
Ans: b
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Admin ;- Bellapuri saikumar
                   ( Sai Saikumar Jn)

Basics For EEE and ECE Students - 3

Q:- Explain Ohm’s law

One the most important & fundamental laws of electronics is the ohms law. This law defines the relationships between current, voltage and resistance. A good way to understand ohms laws is an analogy with a domestic water system.

Thinking how? Let’s see:

Let’s start with the terms present in the definition:

• V = voltage: The easiest way to think of voltage is to call it potential. We know the potential is something which is very useful to do work. Imagine two tanks of water connected with a pipe. If one tank of water is placed higher than the other then there is potential for water to flow from the high level tank to the low level tank. This water pressure is similar to that used to drive electricity around a circuit, called the potential difference, this is measured in volts. This potential difference is provided by a battery or in the case of huge electricity a generator at the generating station.

• I = current: As the water flows through the pipe in a water system due to potential difference ,in the same way an electric current flows through a copper wire. So, current is simply the transfer of something from one place to another. The standard unit of electric current is one ampere that is the current produced by a one volt source in a circuit having a resistance of one ohm.

• R = resistance: Resistance meaning anything that opposes the flow of current. In this case of two tanks of water connected by a pipe, imagine resistance is formed by the pipe. As the pipe gets wider, more water flows & as the pipe gets narrower, less water flows. If there were no pipe between the two bodies of water, we can say there is infinite resistance. The unit by which electrical resistance is measured is Ohm & one ohm is equal to the current of one ampere which will flow when a voltage of one volt is applied.

Now that you got the concept ohm, volt and ampere, so now it’s the time to introduce you to the relationship in between them that is ohms law. The statement is, the electric current passing through a conductor is directly proportional to the potential difference across it, provided that the temperature remains constant. The constant of proportionality is the resistance of the conductor.

The definition above simply states that the current passing through a conductor increases if you increase the voltage.

So, we can say: V proportional to I

Thus, V = IR, Where , V = potential difference in volts (V)

I = current in amps (A) and

R = the constant of proportionality that is the resistance.
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2Q:- What is Ohm’s Law?

Before defining ohms law let us first discuss about the electrical resistance. Electrical resistance is the property of a material by virtue of which it opposes the flow of electrons through a material i.e. conductor. Thus, resistance restricts the flow of electric current through the metallic conductor. The unit of resistance is ohm (Ω), which is obtained from ohms law .

Ohm's law states that physical condition being unchanged , the current through any conductor is directly proportional to the applied potential difference across it.

It can be expressed as V ∝ I

or, V = R × I

Here R is the constant of proportionality and is termed as resistance .

Therefore we an get R = V / I

Applications and limitations of of ohms law:

Ohms law is applicable for any bilateral circuit . It cannot be used for any unilateral network i.e circuits consisting of transistors, diodes etc.Elements which obey ohms law are called ohmic or linear elements . This law is not applicable for non linear elements ie thyristors.
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Admin :- Sai Saikumar Jn ( Bellapuri saikumar)

Basics For EEE & ECE Students - 2

Q:- What is electrical potential ?

Whenever a piece of mass is lifted above the ground level, against gravity, some work is to be done. The quantity of work is done, due to this lifting, is the product of gravitational force on the mass and the height the mass has been lifted. This work done, is added in the potential energy of the mass.

Now think about an electrical charge which is entered in an electric field. As per nature of the charge, it will be attracted or repelled by the field. When the charge will move in the electric field, the work will be done against or by the electric force acting on the charge. So there must be some potential energy gained or lost due to this movement. Hence potential in an electric field is exactly the same as potential in the gravitational field.

So potential at any point in an electrical field, is the work done due to movement of a unit positive charge to that point from infinitely long distance.

The potential difference of two points in an electric field is defined as the net work to be done for moving one unit positive charge from lower potential to the higher potential point.

What is the unit of electrical potential difference?

If the unit of charge in the above definition is taken as one Coulomb and the work done, is one Joule for bringing this one Coulomb charge from one point to another, then the potential difference of these two points is considered as unity and it is denoted as one Volt.

If work done in bringing a positive charge of one coulomb from one point to another in an electric field is one joule, then the potential difference between the said points is considered as one Volt.
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2Q:-  Proper definition of electric current?

Actually, before coming to the question that what is electric current, we need to know what is electricity. Now in some easier words, electricity can be defined as the movement of free electrons across any materials. The outer electrons of an atom is loosely attached with the nucleus, so not much energy is required to de touch this loosely bond electrons from the atom. So when the excitation is provided properly, this electrons get detached from the atom. As well as when these electrons collide with other loosely bond electrons, ultimately the no. of free electrons increases in the matter. And finally when this electrons flow from higher potential to lower potential, we can term that flow as electric current, which flows through the conductor. Now measurement of electric current is done on the basis of the charge of electrons because current is nothing but flow of electrons from higher potential to lower potential.

Now, as charge of an electron is = − 1.6021 × 10^{− 19} coulomb. So, the unit of electric current is expressed as coulomb/sec. Because, this term defines the no. of electrons flowing through a cross section of the conductor. Now coulomb/second is termed as Ampere(A). So the SI unit of electric current flow is Ampere(A).
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Admin:- Sai Saikumar Jn ( Bellapuri saikumar)

Basics for EEE & ECE Students - 1

Q:- What is a linear element

In an electrical network, a linear element shows the linear characteristics in between voltage & current. That is the current passing through a linear element is changed according to the change in the voltage across its terminals.

An important phenomenon of any linear element is the properties of the linear element do not change with the change of applied voltage or the circuit current. Resistors, inductors, capacitors are linear elements as their resistances, inductances, capacitances do not change with a change in applied voltage or the circuit current.

A circuit which is made with only linear elements, is called linear network. Sometime this type of circuit is very useful where voltage versus current relationship should remain linear & any signal distortion is not required.
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2Q:- What is a nonlinear element?

In an electrical network, a non-linear shows the non-linear characteristics in between voltage & current. More specifically, in case of a non-linear element the current passing through it does not change linearly with the linear change in applied voltage at a particular frequency.

An important phenomenon of any non-linear element is they can can distort a given signal. As, they shows non-linear characteristics in between voltage & current so, their current versus voltage curve is not a straight line.

As a instance, we can say a transistor is a non-linear element as the current through it is a non-linear function of the voltage across its terminals. Actually, vacuum tubes, semiconductor devices like diodes, transistors are the non-linear elements.
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3Q:- What is a unilateral element ?

Suppose, an electrical element is connected with a voltage source. If the element is unilateral, then whenever there is a change is occurred in the polarity of the applied voltage, that is the positive & negative terminal of the source altered, the magnitude of the current passing through the element is affected by the polarity change.

Think about a simple diode, which is connected with a voltage source. If somehow the polarity is changed, that is the (+) & (−) terminal interchanged, then the diode will not work. So, we can say, diode is an unilateral element. A important feature of an unilateral element is, it offer varying impedances with variations in flow of current.

Basically, semiconductor devices like diodes, transistors, operational amplifiers are the unilateral element.
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4Q:- What is a bilateral element

Suppose, an electrical element is connected with a voltage source. In case of a bilateral element, if any change occurred in the polarity of the applied voltage, the magnitude of the current passing through the element is not affected by that polarity change.

Lets make it simpler. Think " a " terminal is the positive terminal & terminal " b " is negative terminal of any voltage source. If the legs of a bilateral element altered their position, then the current through it will not affected.

Think about a simple resistor, which is connected with a voltage source. If somehow the polarity is changed, that is the (+) & (−) terminal interchanged, then the current passing through it does not affected, that is the resistor still in same working condition.

A important feature of the bilateral element is, it offers the same impedance irrespective of direction of flow of current. A resistor or a light bulb is the example of bilateral element.
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5Q:- What is electric charge?

We generally hear about the terms 'positive charges', 'negative charges'. These two types of charges are present in the nature. The classification of charges comes from a very simple logic. The electric charge and the nature of charge is determined by the electrons. The loosely bonded electrons from the outer layer of an atom are pretty easy to de touch. Sometimes for matters with high electro negativity, excess electrons can attached with its atom. Depending on this, the nature and magnitude of charge can be determined. Now if there is extra electron in the matter then that can be termed as negatively charged. Because, the charge of electron is negative that means presence of extra electrons make a matter negatively charged. Similarly if there are no extra electrons, the matter is not charged at all and if there is deficiency of electrons, i.e electrons of outer layers have de touched, then there are more protons compared to electrons. So, the matter becomes positively charged.

Electrons and protons are considered as elementary charges. Their electric charge is 1.602 × 10⁻¹⁹ coulombs and for electrons, this is negative and for protons this is positive. Now, two negatively or two positively charged matters repels each other, whereas there is attraction between two different types of charged matters. The intensity of the attraction or repletion force is determined by the amount of charge in the matter.
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Admin:- sai saikumar jn ( Bellapuri saikumar)

Electric Circuits and Ohm's Law : Concepts -- 2 ( sai saikumar jn )

 

Electric Circuits and Ohm's Law : Concepts

 

Resistances in Parallel :

When conductors are joined in parallel, following relations hold good

I = I₁ + I₂ + I₃

1 / R= 1 / R₁ + 1 / R₂ + 1 / R₃

R= ( R₁ +R₂ + R₃ ) / ( R₁R₂ + R₂R₃ + R₃R₁ )

G = G₁ + G₂ + G₃

Effect of Temperature on Resistance :

Resistance of all materials is affected by the variations in temperature. The effect of temperature in general is as follows:
(i) Resistance of most of the metallic conductors increases with rising temperature
(ii) Resistance of non-conductors or insulators usually decreases with rising temperature.

Temperature coefficient of resistance :

It is defined as the increase in resistance per ohm original resistance per
^oC rise in temperature. Thus

α = (R_t - R_o )/(R_o . t)

where
R_o = resistance at 0 ^oC
R_t = resistance at t °C
t = temperature rise in ^oC
Usually
α is of the order of l0 ^-4 Ω/ Ω ^oC for most of the metals.
In case of insulators and electrolytes, α is usually negative.
Temperature coefficient of carbon is negative.

Resistor color coding :

Carbon resistors are physically small in size and color code is used to represent their value in ohms. The scheme is shown in Figure above. Various codes for colors are given in the table below :

Color Code
Color	Value
Black	0
Brown	1
Red	2
Orange	3
Yellow	4
Green	5
Blue	6
Violet	7
Grey	8
White	9

DRIFT VELOCITY :

The drift velocity v_d of charge carriers is related to current I by the equation
 
I = n α e v_d

Where

n = density of charge carriers in conductor,
α = area of cross-section of conductor,
e = charge on each carrier.

A large amount of energy has to be supplied to pull an electron from inside to outside of the metal surface. This energy is called work function. This energy is the characteristic of the metal.

SUPER-CONDUCTIVITY :

As temperature of metallic conductor decreases, their resistivity decreases. In certain metallic conductors as temperature decreases, the resistivity falls to zero at a certain temperature called super-conducting temperature. It happens for mercury at 4 K and for tin at 3.72 K. This phenomenon is called super-conductivity.
Resistivity of semiconductors decreases with increase in temperature

ρ_T = ρ_o e-^{(Eg / kT)}

where

Eg = band gap energy,
ρ_T = resistivity at T K,
k = Boltzman constant.

NON LINEAR DEVICES :

The devices for which potential difference V Vs current I curve is not a straight line are called non-linear devices. They do not obey Ohm's law and resistance of these devices is a function of V or I e.g. vacuum tubes, junction diodes, thermistors etc.
The dynamic resistance of such devices is given as

r = Lt_{∆ t → 0} ∆ V / ∆ I = d V / d I

where

∆V is the change in p.d.

from  ur's -- Bellapuri saikumar
                          ( www.facebook.com/saikumar544)
 

Electric Circuits and Ohm's Law : Concepts --- 1 ( sai saikumar jn)

 Electric Circuits and Ohm's Law : Concepts

BASIC DATA ABOUT ATOM :

Mass of electron = 9.11 x 10^-31 kg
Mass of proton = 1.67 x 10^-27 kg
Mass of neutron = mass of proton
Mass of electron = 1/1840 mass of proton
Diameter of nucleus is of the order of 10^-14 m
Diameter of orbits = 10⁴ times dia of molecule
Diameter of electron = 10^-15 m
Charge on electron = - 1.602 x 10^-19 coulomb
Charge on proton = + 1.602 x 10^-19 coulomb.

UNIT OF CURRENT :

The charge on an electron is measured in terms of coulomb. The unit of current is coulomb per second and is called ampere.Thus

I (Ampere) = coulomb/second = ∆ q / ∆ t One coulomb is equivalent to the charge of 6.28 x 10¹⁸ electrons.
1 emu of current = 3 x 10¹⁰ esu of current.

ELECTROMOTIVE FORCE :

Electromotive force or potential of a body is the work done in joules to bring a unit electric charge from infinity to the body. It is expressed in terms of volts (V).
The potential difference is defined as that which causes current to flow in the closed circuit.

RESISTANCE :

Resistance is the property of a substance due to which it opposes the flow of electrons (i.e., electric current) through it. The unit of resistance is ohm (Ω).
Metals, acids and salt solutions are good conductors of electricity. Silver, copper and aluminium offer least resistance to flow of current and are called very good conductor of electricity. The electrons while flowing through the molecules or the atoms of the conductor, collide with other atoms and electrons, thereby producing heat.
Some substances offer relatively greater difficulty or hindrance to the passage of these electrons. Such substances are called poor conductors or insulators of electricity. Some of the insulators are glass, bakelite, mica, rubber, polyvinyl chloride (P.V.C.), dry wood, etc.

The resistance of a conductor depends on:

1. Length of conductor- it varies directly with the length
2. Cross-sectional area of the conductor - it varies inversely with the cross-sectional area
3. Its resistivity i.e. the nature of composition, etc., of the material of which the conductor is made up
4. Temperature of the conductor - it almost varies directly with the temperature. Thus R, the resistance of a conductor is given by

R = ρ l / A

where
ρ = specific resistance or resistivity of the material,
l = length of the conductors,
A = cross-sectional area of conductor.

Ohm's Law :

If the temperature and other conditions remain constant, the current through a conductor is proportional to the applied potential difference and it remains constant. Thus

Current = Applied Voltage / Resistance of the circuit

Resistance = Applied voltage / Current in the circuit

Potential across resistance = Current x Resistance.
 

Conditions for Ohm's Law :

1. Ohm's law can be applied either to the entire circuit or a part of a circuit.
2. When ohm's law is applied to a part circuit, part resistance and the potential across the part resistance should be used.
3. The Ohm's law can be applied to DC as well as AC circuits. However, in case of AC circuits impedance Z, is used in place of resistance. Thus

I = E / Z = Applied voltage / Impedance in the circuit

Conductance (G ) :

Conductance is the reciprocal of ( R ) and is measure of the ease with which the current will flow through a substance. Thus

G= 1 / R

The unit of conductance is mho.

ELECTRICAL POWER :

Electrical power is expressed in terms of watts (W) and is given by

W= E x I = I² x R = E² / R

Power is also expressed in terms of
kW ( kilowatt ) ( =1000 W ) or
MW ( megawatt ) which is 1000 kW or 1000,000 W.
 

Electrical Energy :

Electrical energy is expressed in terms of kilowatt hours (kWh). Thus

1 kWh = 1 kW x 1 hour = 1000 watt-hours = 1000 x 60 x 60 watt-sec.

RESISTANCE COMBINATIONS :

Resistances in series :

When resistances are connected in series, same current flows through all resistances, and overall resistance R, is given by

R = R₁ + R₂ + R₃

Also,

V = V₁ + V₂ + V₃ = IR₁+ IR₂ + IR₃ .

From ur's -- Bellapuri saikumar
                             ( www.facebook.com/saikumar544)