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Worksheet on Electromagnetic induction

Q1 According to Faraday's Law of electro magnetic induction:


a) The direction of the induced current is such that it opposes it self

b) The induced emf in the coil is proportional to the rate of change of magnetic flux associated with it

c) The direction of induced emf is such that it opposes it self

d) None of the above



Q2 Magnetic field through a coil is changed with respect to time then emf induced in it then select the incorrect regarding induced emf in coil :-


a) Coil may be made up with wood

b) Coil may be connected with an open circuit c) Coil must be of condcucting nature

d) Induced emf does not depends upon resistance of the coil



Q3 A square loop of side 22 cm is changed to a circle in time 0.4 s. The magnetic field present is 0.2 T. The emf induced is :-


a) - 6.6 mV

b) -13.2 mV c) +6.6 mV

d) + 13.2 mV



Q4 An emf induced in a coil, the linking magnetic flux.

a) Must decrease

b) Must increase c) Must remain constant

d) Can be either increased or decreased



Q5 Faraday law represents :-

a) relation between I and B

b) relation between magnetic force and magnetic field c) relation between e.m.f. and rate of change of flux

d) none of these



Q6 When the current through as a solenoid increases at a constant rate, the induced current.

a) is a constant and is in the direction of the inducing current

b) is a constant and is opposite to the direction of the inducing current c) increase with time and is in the direction of the inducing current

d) increase with time and opposite to the direction of the inducing current



Q7 Which statement is correct from following -

(a) Inductor store energy in the form of magnetic field

(b) Capacitor store energy in the form of electric field

(c) Inductor store energy in the form of electric and magnetic field both

(d) Capacitor store energy in the form of electric and magnetic field both

a) a, b

b) a, c c) b, d

d) b, c



Q8 An LR circuit with a battery is connected at t = 0. Which of the following quantities is not zero just after the connection :-

(a) Current in circuit

(b) Magnetic potential energy in the inductor

(c) Power delivered by the battery

(d) Emf induced in the inductor

a) a, b

b) a, c c) c, d

d) Only d



Q9 When current in a coil is reduced from 2A to 1A in 1 ms, the induced emf is 5V. The inductance of coil is :

a) 5 H

b) 5000 H c) 5 mH

d) 50 H



Q10 The electric power is transferred to a far distance at high potential because:-

a) It stops the wire theft

b) To minimise power loss c) Generator gives only high potential

d) Electric power is transferred early due to high potential



Q11 If primary winding of a transformer were connected to a battery, the current in it will :-

a) Increase

b) Remain constant c) Decrease

d) First (1) then (3)



Q12 Which type of losses does not occur in transformer:-

a) mechanical losses

b) copper losses c) hysteresis losses

d) eddy current losses



Q13 The efficiency of a transformer is maximum, because :-

a) No part of the transformer is in motion

b) It creates maximum voltage c) It creates minimum voltage

d) None of the above



Q14 In order to avoid eddy currents in the core of a transformer :-

a) The number of turns in the secondary coil is made considerably large

b) A laminated core is used c) A step down transformer is used

d) A high voltage alternating weak current is used



Q15 The ratio of the secondary to the primary turns in a transformer is 3 : 2 and the output power is P. Neglecting all power losses, the input power must be :-

a) P/2

b) P c) 2P/3

d) 3P/2



Q16 In transformer, power of secondary coil is:-

a) less than primary coil

b) more than primary coil c) more in step up and less in step down than primary coil

d) more in step down and less in step up than primary coil



Q17 The electric generator produce electric current based on which principle :-

a) Ohm's law

b) Faradays's law of EMI c) Ampere's lawcoil

d) Biot - savart's law



Q18 Assertion :- Inductance coil are made of copper.

Reason :- Copper has very small ohmic resistance.

a) A

b) B c) C

d) D



Q19 Assertion :- An emf is induced in long solenoid by a small bar magnet that moves while totally inside it along the solenoid axis.

Reason :- As the magnet moves inside the solenoid, the flux through individual turns of the solenoid does not change.

a) A

b) B c) C

d) D



Q20 Assertion :-The coils in the resistance boxes are made by doubling the wire.

Reason :- When two coils are wound on each other, the mutual inductance is zero.

a) A

b) B c) C

d) D



Q21 Assertion :- Induced electric field lines form closed loops in space.

Reason :- Induced electric field lines do not originate & terminate at charge particle.

a) A

b) B c) C

d) D



Q22 Assertion :- MRI is an excellent method to find problem in internal tissues.

Reason :- Two third of the human body is made up of hydrogen which has one electron.

a) A

b) B c) C

d) D



Q23 Assertion :- In a step down transformer, value of voltage in secondary coil is less than in primary.

Reason :- Linked magnetic flux in secondary is less than in primary.

a) A

b) B c) C

d) D



Q24 Assertion :- In higher power transmission, 240 V is preferred over 120 V.

Reason :- Power loss is more in case of 120 V as compared to 240 V.

a) A

b) B c) C

d) D



Q25 The number of turns of a solenoid are doubled without changing its length and area of cross-section. The self-inductance of the solenoid will become.......... times.

a) 3 times

b) 4 times c) 5 times

d) 6 times



Q26 The magnetic flux linked with a coil changes by 2 X 10 to the power (-2) Wb when the current changes by 0.01 A. The self-inductance of the coil is.............

a) 2 Henry

b) 4 Henry c) 6 Henry

d) 8 Henry



Q27 The self-inductance L of a solenoid of length 'l' and area of cross-section A, with a fixed number of turns N increases as:

a) both 'l' and A increases

b) there is a varying current in A c) there is no current in A

d) there is a constant current in the counter clockwise direction in A



Q28 The direction of induced emf can be found by.

a) Kirchhoff's voltage law

b) Kirchhoff's current law c) Lenz's law

d) Fleming's Right hand rule



Q29 Which of the following is the unit of inductance?

a) ohm

b) Henry c) Ampere-turns

d) Weber/metre



Q30 The unit of magnetic flux in SI is:

a) Weber

b) Gauss c) Oersted

d) Tesla



Q31 Which of the following phenomena makes use of electromagnetic induction?

a) Charging a storage battery

b) Magnetizing an iron piece with a bar magnet c) Generation of hydroelectricity

d) Magnetizing a soft iron piece by placing inside a current carrying solenoid



Q32 Which of the following is based on the law of conservation of energy?

a) Lenz's law

b) Faraday's law c) Ampere's law

d) Bio Savart law



Q33 The induced emf cannot be produced by.

a) moving a magnet near a circuit

b) moving a circuit near a magnet c) changing the current in one circuit placed near the other

d) maintaining large but constant current in a circuit



Q34 Dynamo is designed on the principle of.

a) Electromagnetic induction

b) Self-induction c) Mutual induction

d) None of these



Q35 What does a dynamo generate?

a) Electrons

b) Charge c) emf

d) None of these



Q36 What is motional emf? It is the induced emf:

a) across the ends of a wire moving in a magnetic field

b) in a coil due to the motion of the magnet near it c) in a circuit due to variation in its own current

d) in a circuit due to the variation of current in the neighbouring circuit



Q37 The force between two current-carrying parallel wires is due to:

a) Electrostatic interaction

b) Magnetic effect of electric current c) Electric effect of magnetic field

d) Electromagnetic induction



Q38 The current from which of the following devices does not vary in magnitude?

a) Transformers

b) Dynamo c) Cell

d) Induction coil



Q39 Which of the following instruments do not make use of eddy currents?

a) Electrical brakes

b) Induction motor c) Transformer

d) Dead beat galvanometer



Q40 What is the minimum value of inductance that can be obtained with the help of three inductances of 2 H, 3 H and 6 H?

a) H/6

b) H/3 c) 1H

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Q41 No current is drawn from the secondary coil of an ideal transformer. What is the power factor of the primary coil?

a) 1/2

b) 1 c) infinite

d) Zero



Q42 The Lenz's law is the consequence to the conservation of.

a) charge

b) momentum c) energy

d) none of these



Q43 When the number of turns of a coil is doubled, its self inductance:

a) is doubled

b) is halved c) becomes one quarter

d) becomes four times



Q44 Eddy currents do not cause:

a) damping

b) heating c) sparking

d) loss of energy



Q45 The role of inductance is equivalent to:

a) momentum

b) force c) energy

d) inertia



Q46 The current in the armature of dc motor is the maximum, when the motor is:

a) switched off

b) switched on c) running at full speed

d) running at intermediate speed



Q47 A coil is wound on a transformer of rectangular cross-section. If all the linear dimensions of the transformer are increased by a factor 2 and the number of turns per unit length of the coil remains unchanged, the self-inductance of the coil will be increased by a factor:

a) 16

b) 8 c) 4

d) 2



Q48 What is the energy stored in a 50 mH inductor carrying a current of 4A?

a) 0.4 J

b) 0.2 J c) 0.1 J

d) 0.05 J



Q49 A step-up transformer raises the voltage from 220V to 11000 V. If the number of turns of the secondary be 1000, what is the number of turns of the primary?

a) 2

b) 20 c) 200

d) 2000



Q50 Eddy current can be minimized by using.

a) thick wires

b) thin sheets of metal c) thick sheets

d) laminated sheets





ANSWERS



1) b

2) c

3) a

4) d

5) c

6) b

7) a

8) d

9) c

10) b

11) b

12) a

13) a

14) b

15) b

16) a

17) b

18) a

19) d

20) c

21) a

22) c

23) a

24) a

25) b

26) a

27) b

28) c

29) b

30) a

31) b

32) a

33) d

34) a

35) c

36) a

37) b

38) c

39) c

40) c

41) d

42) c

43) d

44) c

45) d

46) b

47) b

48) a

49) b

50) d



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