255 + Interview Questions in ELECTROMAGNETIC INDUCTION IN GENERAL AWARENESS Page 2 InterviewSolution

51.

Distinguish between a step-up and a step-down transformers.

Answer»

Step-up transformer	Step-down transformer
1. The output voltage is more than the input voltage.	1. The output voltage is less than the input voltage.
2. The number of turns of the secondary coil is more than that of the primary coil.	2. The number of turns of the secondary coil is less than that of the primary coil.
3. The output current is less than the input current.	3. The output current is more than that of the input current.
4. The primary coil is made of thicker copper wire than the secondary coil.	4. The secondary coil is made of thicker copper wire than the primary coil.

Discussion

52.	Type of impedance Phase between voltage and current(i) Resistance(a) 90° lead(ii) Inductance(b) between 0° and 90° (iii) Capacitance(c) 0° (iv) RLC(d)90° lag
Answer» (i) → (c) (ii) → (d) (iii) → (a) (iv) → (b)

52.

Type of impedance Phase between voltage and current(i) Resistance(a) 90° lead(ii) Inductance(b) between 0° and 90° (iii) Capacitance(c) 0° (iv) RLC(d)90° lag

Answer»

(i) → (c)

(ii) → (d)

(iii) → (a)

(iv) → (b)

Discussion

53.	An aircraft of wing span of 50 m flies horizontally in earth’s magnetic field of 6 × 10-5 T at a speed of 400 m/s. Calculate the emf generated between the tips of the wings of the aircraft.
Answer» Data : l = 50 m, B = 6 × 10^-5 T, v = 400 m/s The magnitude of the induced emf, \|e\| = Blv = (6 × 10^-5)(400)(50) = 1.2V

53.

An aircraft of wing span of 50 m flies horizontally in earth’s magnetic field of 6 × 10-5 T at a speed of 400 m/s. Calculate the emf generated between the tips of the wings of the aircraft.

Answer»

Data : l = 50 m, B = 6 × 10^-5 T, v = 400 m/s

The magnitude of the induced emf,

|e| = Blv = (6 × 10^-5)(400)(50) = 1.2V

Discussion

54.	Magnetic flux linked with a closed loop at a certain instant of time is zero. Does it imply that that induced emf at that instant is also zero?
Answer» No. The emf does not depend on the magnetic flux but on the change of magnetic flux.

Discussion

55.	On what factors does the magnitude of the emf induced in the circuit due to magnetic flux depend?
Answer» It depends on the rate of change in magnetic flux (or simply change in magnetic flux) \|ω\| = \(\frac{Δφ}{Δt}\)

55.

On what factors does the magnitude of the emf induced in the circuit due to magnetic flux depend?

Answer»

It depends on the rate of change in magnetic flux (or simply change in magnetic flux)

|ω| = \(\frac{Δφ}{Δt}\)

Discussion

56.	What is meant by wattles current?
Answer» The component of current (I_RMS sin φ), which has a phase angle of \(\frac{π}{2}\) with the voltage is called reactive component. The power consumed is zero. So that it is also known as ‘Wattless’ current.

Discussion

57.	A horizontal wire 20 m long extending from east to west is falling with a velocity of 10 m/s normal to the Earth’s magnetic field of 0.5 × 10-4 T.What is the value of induced emf in the wire?
Answer» Data : l = 20 m, v = 10 m/s. B = 5 × 10^-5 T The magnitude of the induced emf, \|e\| = Blv = (5 × 10^-5 )(20)(10) = 10^-2 V = 10 mV

57.

A horizontal wire 20 m long extending from east to west is falling with a velocity of 10 m/s normal to the Earth’s magnetic field of 0.5 × 10-4 T.What is the value of induced emf in the wire?

Answer»

Data : l = 20 m, v = 10 m/s. B = 5 × 10^-5 T

The magnitude of the induced emf,

|e| = Blv = (5 × 10^-5 )(20)(10) = 10^-2 V = 10 mV

Discussion

58.	A horizontal straight wire 10 m long extending from east to west is falling with a speed of 5.0 m s-1, at right angles to the horizontal component of the earth’s ‘ magnetic field, 0.30 × 104 Wbm2.(a) What is the instantaneous value of the emf induced in the wire?(b) What is the direction of the emf?(c) Which end of the wire is at the higher electrical potential?
Answer» Here, length of the wire, l = 10m; Velocity of the wire, V = 5.0 ms¹ Horizontal component of earth’s magnetic field, B_H = 0.30 x 10^-4Wb m^-2 (a) Now, e = B_Hl_v = 0.30 x 10^-4x 10 x 5.0 = 1.5 x 10^-3 V (b) The induced e.m.f. will be set up from west to east end. (c) The eastern end will be at higher potential.

Discussion

59.	A coil of cross sectional area 400 cm2 having 30 turns is making 1800 rev/min in a magnetic field of IT. The peak value of the induced emf is-(a) 113 V (b) 226 V (c) 339 V (d) 452 V
Answer» (b) 226 V ε_m = NBA ω = 30 x 1 x 400 x 10^-4 x 30 x 2π = 226 V

59.

A coil of cross sectional area 400 cm2 having 30 turns is making 1800 rev/min in a magnetic field of IT. The peak value of the induced emf is-(a) 113 V (b) 226 V (c) 339 V (d) 452 V

Answer»

(b) 226 V

ε_m = NBA ω = 30 x 1 x 400 x 10^-4 x 30 x 2π = 226 V

Discussion

60.	A plane coil of lo turns is tightly wound around a solenoid of diameter 2 cm having 400 turns per centimeter. The relative permeability of the core is 800. Calculate the mutual inductance.
Answer» Data: N = 10, R = 1 cm = 10^-2 m, n = 400 cm^-1 = 4 × 10⁴ m^-1 , k = 800, μ₀ = 4π × 10⁴ H/m Mutual inductance M = kμ₀πR²nN =(800)(4π × 10^-7)[π × (10²)² ](4 × 10⁴)(10) = 0.1264 H

60.

A plane coil of lo turns is tightly wound around a solenoid of diameter 2 cm having 400 turns per centimeter. The relative permeability of the core is 800. Calculate the mutual inductance.

Answer»

Data: N = 10, R = 1 cm = 10^-2 m,

n = 400 cm^-1 = 4 × 10⁴ m^-1 , k = 800,

μ₀ = 4π × 10⁴ H/m

Mutual inductance

M = kμ₀πR²nN

=(800)(4π × 10^-7)[π × (10²)² ](4 × 10⁴)(10)

= 0.1264 H

Discussion

61.	A wire in the form of a tightly wound solenoid is connected to a DC source, and carries a current. If the coil is stretched so that there are gaps between successive elements of the spiral coil, will the current increase or decrease? Explain.
Answer» The current will increase. As the wires are pulled apart the flux will leak through the gaps. Lenz’s law demands that induced e.m.f. resist this decrease, which can be done by an increase in current.

Discussion

62.	Two tightly wound solenoids have the same length and circular cross-sectional area, but the wire of solenoid 1 is half as thick as solenoid 2. The ratio of their inductances is(A) \(\cfrac14\)(B) \(\cfrac12\)(C) 2 (D) 4
Answer» Correct option is (D) 4

Discussion

63.	A coaxial cable, whose outer radius is five times its inner radius, is carrying a current of 1.5 A. What is the magnetic field energy stored in a 2 m length of the cable ?
Answer» Data : b/a = 5, I = 1.5A, l = 2m, \(\cfrac{μ_0}{4π}\) = 10^-7 H/m The total magnetic energy in a given length of a current-carrying coaxial cable, U_m = \(\left(\cfrac{μ_0}{4π}\right)\) I²l log_e \(\cfrac ba\) Therefore, the required magnetic energy is U_m = (10^-7)(1.5)² (2)log_e 5 = 4.5 × 10⁷ × 2.303 × log₁₀ 5 = 4.5 × 10^-7 × 2.303 × 0.6990 = 7.24 × 10^-7 J

63.

A coaxial cable, whose outer radius is five times its inner radius, is carrying a current of 1.5 A. What is the magnetic field energy stored in a 2 m length of the cable ?

Answer»

Data : b/a = 5,

I = 1.5A, l = 2m, \(\cfrac{μ_0}{4π}\) = 10^-7 H/m

The total magnetic energy in a given length of a current-carrying coaxial cable,

U_m = \(\left(\cfrac{μ_0}{4π}\right)\) I²l log_e \(\cfrac ba\)

Therefore, the required magnetic energy is

U_m = (10^-7)(1.5)² (2)log_e 5

= 4.5 × 10⁷ × 2.303 × log₁₀ 5

= 4.5 × 10^-7 × 2.303 × 0.6990 = 7.24 × 10^-7 J

Discussion

64.	What are phasors?
Answer» A sinusoidal alternating voltage (or current) can be represented by a vector which rotates about the origin in anti-clockwise direction at a constant angular velocity ω. Such a rotating vector is called a phasor.

Discussion

65.	How will you define RMS value of an alternating current?
Answer» RMS value of alternating current is defined as that value of the steady current which when flowing through a given circuit for a given time produces the same amount of heat as produced by the alternating current when flowing through the same circuit for the same time.

Discussion

66.	In an AC circuit, the rms value of the current Irms , is related to the peak current I0 as-(a) Irms = \(\frac{I_0}{2}\)(b) Irms = \(\frac{I_0}{\sqrt2}\)(c) Irms = √2l0(d)Irms = πl0
Answer» Correct answer is (b) I_rms = \(\frac{I_0}{\sqrt2}\)

Discussion

67.	Calculate the instantaneous value at 60° , average value and RMS value of an alternating current whose peak value is 20 A.
Answer» Peak value of current, I = 20 A Angle, θ = 60° [θ = ωt] (i) Instantaneous value of current, i = l_msin ωt = I_m sin θ = 20 sin 60° = 20 x \(\frac{\sqrt 3}{2}\) = 10√3 = 10 x 1.732 i = 17.32 A (ii) Average value of current, l_av= \(\frac{2I_m}{π}\) = \(\frac{2 \times 20}{3.14}\) (iii) RMS value of current, I_RMS= 0.707 I_m or \(\frac{I_m}{\sqrt2}\) = 0.707 x 20 I_RMS = 14.14 A

67.

Calculate the instantaneous value at 60° , average value and RMS value of an alternating current whose peak value is 20 A.

Answer»

Peak value of current, I = 20 A

Angle, θ = 60° [θ = ωt]

(i) Instantaneous value of current,

i = l_msin ωt = I_m sin θ

= 20 sin 60° = 20 x \(\frac{\sqrt 3}{2}\) = 10√3 = 10 x 1.732

i = 17.32 A

(ii) Average value of current,

l_av= \(\frac{2I_m}{π}\) = \(\frac{2 \times 20}{3.14}\)

(iii) RMS value of current,

I_RMS= 0.707 I_m

or \(\frac{I_m}{\sqrt2}\) = 0.707 x 20

I_RMS = 14.14 A

Discussion

68.	The power loss is less in transmission lines when ……
Answer» The power loss is less in transmission lines when voltage is more but current is less.

Discussion

69.	In an electrical circuit, R, L, C and AC voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and current in the circuit is \(\frac{1}{2}\). Instead, if C is removed from the circuit, the phase difference is again \(\frac{π}{3}\). The power factor of the circuit is-(a) \(\frac {1}{2}\)(b) \(\frac {1}{\sqrt2}\)(c) 1(d) \(\frac{\sqrt3}{2}\)
Answer» Correct answer is (c) 1

Discussion

70.	What is meant by sinusoidal alternating voltage?
Answer» If the waveform of alternating voltage is a sine wave, then it is known as sinusoidal alternating voltage, which is given by the relation. υ = V_m sin ωt

Discussion

71.	AC power is transmitted from a power house at a high voltage as-(a) the rate of transmission is faster at high voltages (b) it is more economical due to less power loss (c) power cannot be transmitted at low voltages (d) a precaution against theft of transmission lines
Answer» (b) it is more economical due to less power loss

Discussion

72.	A 40 Ω electric heater is connected to 200 V, 50 Hz main supply. The peak value of the electric current flowing in the circuit is approximately- (a) 2.5 A (b) 5 A (c) 7 A (d) 10 A
Answer» (c) 7 A l_{0 = \(\frac{V_0}{R}\)= \(\frac{200{\sqrt2}}{40}\)} 5 √2 ≈ 7A

72.

A 40 Ω electric heater is connected to 200 V, 50 Hz main supply. The peak value of the electric current flowing in the circuit is approximately- (a) 2.5 A (b) 5 A (c) 7 A (d) 10 A

Answer»

(c) 7 A

l_{0 = \(\frac{V_0}{R}\)= \(\frac{200{\sqrt2}}{40}\)} 5 √2 ≈ 7A

Discussion

73.	Alternating current can be measured by(a) moving coil galvanometer (b) hot wire ammeter (c) tangent galvanometer (d) none of the above
Answer» Correct answer is (b) hot wire ammeter

Discussion

74.	In an AC circuit with voltage V and current I, the power dissipated is-(a) VI(b) \(\frac{1}{2}\)VI(c) \(\frac{1}{\sqrt2}\) VI(d) depends on the phase difference between I and V
Answer» (d) depends on the phase difference between I and V

Discussion

75.	In an LCR circuit, the energy is dissipated in- (a) R only (b) R and L only a(c) R and C only (d) R, L and C
Answer» Correct answer is (a) R only

Discussion

76.	In a LCR AC circuit off resonance, the current- (a) is always in phase with the voltage (b) always lags behind the voltage (c) always leads the voltage (d) may lead or lag behind the voltage
Answer» (d) may lead or lag behind the voltage

Discussion

77.	A metre gauge train is heading north with speed 54 km/h in the Earth’s magnetic field 3 × 10-4 T. The emf induced across the axle joining the wheels is (A) 0.45 mV (B) 4.5 mV (C) 45 mV (D) 450 mV.
Answer» Correct option is (B) 4.5 mV

Discussion

78.	In an electric communication line, the current flows upwards. Considering the Earth’s magnetic field to be negligible, the direction of magnetic field on this electric line is:(a) Towards East(b) Towards West(c) Towards North(d) Towards South
Answer» (a) Towards East According to the right hand thumb rule, the magnetic field will in the east direction.

Discussion

79.	When current in a coil changes with time, how is the back emf induced in the coil related to it?
Answer» The back emf induced in the coil opposes the change in current.

Discussion

80.	State the steady value of the reading of the ammeter in the circuit shown below :
Answer» State the steady value of zero.

Discussion

81.	Class 12 Physics MCQ Questions of Electromagnetic Induction with Answers?
Answer» We have provided Class 12 MCQ Questions with Answers to help students understand the concept very well. Solving the MCQ Questions of Class 12 Physics can be of extreme help as you will be aware of all the concepts. These MCQ Questions of Electromagnetic Induction Class 12 with answers pave for a quick revision of the Chapter thereby helping you to enhance subject knowledge. Class 12 Physics MCQ Questions of Electromagnetic Induction with Answers with Answers were prepared based on the latest exam pattern. Have a check once the MCQ Questions Physics Class 12 and cross-check your answers during preparation. Practice MCQ Question for Class 12 Physics chapter-wise 1. The coupling co-efficient of the perfectly coupled coils is: (a) Zero (b) 1 (c) slightly more than 1 (d) infinite 2. The role of inductance is equivalent to: (a) inertia (b) force (c) energy (d) momentum 3. A choke is used as a resistance in : (a) dc circuits (b) ac circuits (c) both ac and dc circuits (d) neither (a) nor (b) 4. The SI unit of magnetic flux is: (a) T (b) Tn^-2 (c) Wb (d) Wb m^-2 5. For purely capacitive circuits, power factor is: (a) 0 (b) -1 (c) 1 (d) infinity 6. The core of a transformer is laminated because: (a) rusting of core may be prevented (b) ratio of voltage in primary and secondary may be increased. (c) energy losses due to eddy current may be minimised (d) The weight of transformer may be reduced 7. Whenever the magnetic flux linked with an electric circuit changes, an emf is induced in the circuit. This is called (a) electromagnetic induction (b) lenz’s law (c) hysteresis loss (d) kirchhoff’s laws 8. Lenz’s law is a consequence of the law of conservation of (a) charge (b) mass (c) energy (d) momentum 9. When current i passes through an inductor of self inductance L, energy stored in it is 1/2. Li². This is stored in the (a) current (b) voltage (c) magnetic field (d) electric field 10. Eddy currents are produced when (a) A metal is kept in varying magnetic field (b) A metal is kept in the steady magnetic field (c) A circular coil is placed in a magnetic field (d) Through a circular coil, current is passed 11. According to Faraday’s law of electromagnetic induction (a) electric field is produced by time varying magnetic flux (b) magnetic field is produced by time varying electric flux. (c) magnetic field is associated with a moving charge. (d) None of these 12. A moving conductor coil produces an induced e.m.f. This is in accordance with (a) Lenz’s law (b) Faraday’s law (c) Coulomb’s law (d) Ampere’s law 13. A coil of insulated wire is connected to a battery. If it is taken to galvanometer, its pointer is deflected, because (a) the induced current is produced (b) the coil acts like a magnet (c) the number of turns in the coil of the galvanometer are changed (d) None of these 14. The laws of electromagnetic induction have been used in the construction of a (a) galvanometer (b) voltmeter (c) electric motor (d) generator 15. Two identical coaxial circular loops carry a current i each circulating in the same direction. If the loops approach each other, you will observe that the current in (a) each increases (b) each decreases (c) each remains the same (d) one increases whereas that in the other decreases 16. Magnetic flux is (a) total charge per unit area (b) total current through a surface (c) total number of magnetic field lines passing normally through given area (d) total e.m.f. in closed circuit 17. A conducting loop is placed in a uniform magnetic field with its plane perpendicular to the field. An e.m.f. is induced in the loop, if (a) it is translated (b) it is rotated about its axis (c) both (a) and (b) (d) it is rotated about its diameter 18. Eddy currents do not produce (a) heat (b) a loss of energy (c) spark (d) damping of motion 19. A coil of insulated wire is connected to a battery. If it is connected to galvanometer, its pointer is deflected, because (a) induced current is set up (b) no induced current is set up (c) the coil behaves as a magnet (d) the number of turns is changed 20. Direction of current induced in a wire moving in a magnetic field is found using (a) Fleming’s left found rule (b) Fleming’s right hand rule (c) Ampere’s rule (d) Right hand clasp rule 21. The polarity of induced emf is given by (a) Ampere's circuital law (b) Biot-Savart law (c) Lenz’s law (d) Fleming's right hand rule 22. The coils in resistance boxes are made from doubled insulated wire to nullify the effect of (a) heating (b) magnetism (c) pressure (d) self induced e.m.f. 23. The magnetic potential energy stored in a certain inductor is 25 mJ, when the current in the inductor is 60 mA. This inductor is of inductance (a) 0.138 H (b) 138.88 H (c) 13.89 H (d) None of these 24. Which of the following is not the application of eddy currents? (a) Induction furnace (b) Dead beat galvanometer (c) speedometer (d) X-ray crystallography 25. The mutual inductance of a pair of coils is 0.75 H. If current in the primary coil changes from 0.5 A to zero in 0.01 s, find average induced e.m.f. in secondary coil (a) 25.5 V (b) 12.5 V (c) 22.5 V (d) 37.5 V Answer: 1. Answer : (b) 1 Explanation: If the value of k is 1 then the two coils are perfectly coupled or 100% coupling between them. 2. Answer : (a) inertia Explanation: The role of inductance is equivalent to inertia. 3. Answer : (b) ac circuits Explanation: A choke coil is used as resistance in AC circuits. 4. Answer : (c) Wb Explanation: Weber, unit of magnetic flux in the International System of Units (SI), defined as the amount of flux that, linking an electrical circuit of one turn (one loop of wire), produces in it an electromotive force of one volt as the flux is reduced to zero at a uniform rate in one second. 5. Answer : (a) 0 Explanation: Power in circuit (P)=V _rmsI _rmscosϕ = V_rms I_rmscos90^o= 0 6. Answer : (c) energy losses due to eddy current may be minimised Explanation: The core of a transformer is laminated to minimise the energy losses due to eddy currents. 7. Answer : (a) electromagnetic induction Explanation: Whenever the magnetic flux linked with an electric circuit changes, an emf is induced in the circuit. This is called electromagnetic induction. 8. Answer : (c) energy Explanation: Lenz's law is a manifestation of the conservation of energy. The induced emf produces a current that opposes the change in flux, because a change in flux means a change in energy. Lenz's law is a consequence. 9. Answer : (c) magnetic field Explanation: A magnetic field is induced in the space between the inductor. And this magnetic field corresponds to energy. 10. Answer : (a) A metal is kept in varying magnetic field Explanation: They arise when a conductor moves through a magnetic field, or when the magnetic field surrounding a stationary conductor is varying. Summarising, we can say that anything which results in the conductor experiencing a change in the intensity or direction of a magnetic field produces eddy currents. 11. Answer : (a) electric field is produced by time varying magnetic flux Explanation: According to Faraday's Law of electromagnetic induction, if magnetic flux through a coil changes, it leads to an induced emf across the coil. Hence, electric field is produced by time-varying magnetic fields. 12. Answer : (b) Faraday’s law Explanation: Faraday's Law states that when the magnetic flux linking a circuit changes, an electromotive force is induced in the circuit proportional to the rate of change of the flux linkage. This results in a moving conductor coil producing EMF. 13. Answer : (a) the induced current is produced Explanation: When electric current is passed through the coil inside the galvanometer, induction of magnetic field takes place and thus the coil acts like a magnet which experiences torque due to permanent magnet inside galvanometer and thus the pointer is deflected. 14. Answer : (d) generator Explanation: The law of electromagnetic induction have been used in the construction of. In a generator, emf is induced according to Lenz's rule. 15. Answer : (b) each decreases Explanation: As the two identical coaxial circular loops carry a current i each circulating in the same direction, their flux add each other. When the two are brought closer, the total fluc linkage increase. By Lenz's a law a current will be induced in both the loops such that it opposes this change in flux. As the flux increases, the current in each loop will decreases so as to decrease the increasing flux. 16. Answer : (c) total number of magnetic field lines passing normally through given area Explanation: Magnetic flux is a measurement of the total magnetic field which passes through a given area.The angle at which the field line intersects the area is also important. A field line passing through at a glancing angle will only contribute a small component of the field to the magnetic flux. 17. Answer : (d) it is rotated about its diameter Explanation: An emf is induced only when magnetic flux linked with the loop changes. This is possible when the loop is rotated about a diameter. 18. Answer : (c) spark Explanation: Eddy current circulate within the conductor. 19. Answer : (a) induced current is set up Explanation: The angle through which the coil is deflected due to the effect of the magnetic torque is proportional to the magnitude of current in the coil.Therefore, when a coil of insulated wire which is connected to a battery, is taken to a galvanometer. Its pointer would deflect because of the production of induced current. 20. Answer : (b) Fleming’s right hand rule Explanation: Fleming's right hand rule is used to find direction of induced current in a wire moving in a magnetic field. 21. Answer : (c) Lenz’s law Explanation: The polarity of the induced emf or the current in any circuit is such as to oppose the cause that produces it. This is also known as Lenz's law. 22. Answer : (d) self induced e.m.f. Explanation: The coils in resistance boxes are made from doubled insulated wire to nullify the effect of self induced e.m.f. 23. Answer : (c) 13.89 H Explanation: PE = \(\frac{1}{2}LI^2\) \(25\times10^{-3}=\frac{1}{2}(60\times10^{-3})^2\) L = 13.89 H 24. Answer : (d) X-ray crystallography Explanation: Induction furnace, galvanometer damping and speedometer of automobile are the application of eddy currents. Crystallography is done by diffraction. 25. Answer : (d) 37.5 V Explanation: \(e=M\frac{dI}{dt}\) \(=\frac{0.75\times0.5}{0.01}\) = 37.5 V Click here to practice MCQ Question for Electromagnetic Induction Class 12

81.

Class 12 Physics MCQ Questions of Electromagnetic Induction with Answers?

Answer»

We have provided Class 12 MCQ Questions with Answers to help students understand the concept very well. Solving the MCQ Questions of Class 12 Physics can be of extreme help as you will be aware of all the concepts. These MCQ Questions of Electromagnetic Induction Class 12 with answers pave for a quick revision of the Chapter thereby helping you to enhance subject knowledge.

Class 12 Physics MCQ Questions of Electromagnetic Induction with Answers with Answers were prepared based on the latest exam pattern. Have a check once the MCQ Questions Physics Class 12 and cross-check your answers during preparation.

Practice MCQ Question for Class 12 Physics chapter-wise

1. The coupling co-efficient of the perfectly coupled coils is:

(a) Zero
(b) 1
(c) slightly more than 1
(d) infinite

2. The role of inductance is equivalent to:

(a) inertia
(b) force
(c) energy
(d) momentum

3. A choke is used as a resistance in :

(a) dc circuits
(b) ac circuits
(c) both ac and dc circuits
(d) neither (a) nor (b)

4. The SI unit of magnetic flux is:

(a) T
(b) Tn^-2
(c) Wb
(d) Wb m^-2

5. For purely capacitive circuits, power factor is:

(a) 0
(b) -1
(c) 1
(d) infinity

6. The core of a transformer is laminated because:

(a) rusting of core may be prevented
(b) ratio of voltage in primary and secondary may be increased.
(c) energy losses due to eddy current may be minimised
(d) The weight of transformer may be reduced

7. Whenever the magnetic flux linked with an electric circuit changes, an emf is induced in the circuit. This is called

(a) electromagnetic induction
(b) lenz’s law
(c) hysteresis loss
(d) kirchhoff’s laws

8. Lenz’s law is a consequence of the law of conservation of

(a) charge
(b) mass
(c) energy
(d) momentum

9. When current i passes through an inductor of self inductance L, energy stored in it is 1/2. Li². This is stored in the

(a) current
(b) voltage
(c) magnetic field
(d) electric field

10. Eddy currents are produced when

(a) A metal is kept in varying magnetic field
(b) A metal is kept in the steady magnetic field
(c) A circular coil is placed in a magnetic field
(d) Through a circular coil, current is passed

11. According to Faraday’s law of electromagnetic induction

(a) electric field is produced by time varying magnetic flux
(b) magnetic field is produced by time varying electric flux.
(c) magnetic field is associated with a moving charge.
(d) None of these

12. A moving conductor coil produces an induced e.m.f. This is in accordance with

(a) Lenz’s law
(b) Faraday’s law
(c) Coulomb’s law
(d) Ampere’s law

13. A coil of insulated wire is connected to a battery. If it is taken to galvanometer, its pointer is deflected, because

(a) the induced current is produced
(b) the coil acts like a magnet
(c) the number of turns in the coil of the galvanometer are changed
(d) None of these

14. The laws of electromagnetic induction have been used in the construction of a

(a) galvanometer
(b) voltmeter
(c) electric motor
(d) generator

15. Two identical coaxial circular loops carry a current i each circulating in the same direction. If the loops approach each other, you will observe that the current in

(a) each increases
(b) each decreases
(c) each remains the same
(d) one increases whereas that in the other decreases

16. Magnetic flux is

(a) total charge per unit area
(b) total current through a surface
(c) total number of magnetic field lines passing normally through given area
(d) total e.m.f. in closed circuit

17. A conducting loop is placed in a uniform magnetic field with its plane perpendicular to the field. An e.m.f. is induced in the loop, if

(a) it is translated
(b) it is rotated about its axis
(c) both (a) and (b)
(d) it is rotated about its diameter

18. Eddy currents do not produce

(a) heat
(b) a loss of energy
(c) spark
(d) damping of motion

19. A coil of insulated wire is connected to a battery. If it is connected to galvanometer, its pointer is deflected, because

(a) induced current is set up
(b) no induced current is set up
(c) the coil behaves as a magnet
(d) the number of turns is changed

20. Direction of current induced in a wire moving in a magnetic field is found using

(a) Fleming’s left found rule
(b) Fleming’s right hand rule
(c) Ampere’s rule
(d) Right hand clasp rule

21. The polarity of induced emf is given by

(a) Ampere's circuital law
(b) Biot-Savart law
(c) Lenz’s law
(d) Fleming's right hand rule

22. The coils in resistance boxes are made from doubled insulated wire to nullify the effect of

(a) heating
(b) magnetism
(c) pressure
(d) self induced e.m.f.

23. The magnetic potential energy stored in a certain inductor is 25 mJ, when the current in the inductor is 60 mA. This inductor is of inductance

(a) 0.138 H
(b) 138.88 H
(c) 13.89 H
(d) None of these

24. Which of the following is not the application of eddy currents?

(a) Induction furnace
(b) Dead beat galvanometer
(c) speedometer
(d) X-ray crystallography

25. The mutual inductance of a pair of coils is 0.75 H. If current in the primary coil changes from 0.5 A to zero in 0.01 s, find average induced e.m.f. in secondary coil

(a) 25.5 V
(b) 12.5 V
(c) 22.5 V
(d) 37.5 V

Answer:

1. Answer : (b) 1

Explanation: If the value of k is 1 then the two coils are perfectly coupled or 100% coupling between them.

2. Answer : (a) inertia

Explanation: The role of inductance is equivalent to inertia.

3. Answer : (b) ac circuits

Explanation: A choke coil is used as resistance in AC circuits.

4. Answer : (c) Wb

Explanation: Weber, unit of magnetic flux in the International System of Units (SI), defined as the amount of flux that, linking an electrical circuit of one turn (one loop of wire), produces in it an electromotive force of one volt as the flux is reduced to zero at a uniform rate in one second.

5. Answer : (a) 0

Explanation: Power in circuit (P)=V _rmsI _rmscosϕ = V_rms I_rmscos90^o= 0

6. Answer : (c) energy losses due to eddy current may be minimised

Explanation: The core of a transformer is laminated to minimise the energy losses due to eddy currents.

7. Answer : (a) electromagnetic induction

Explanation: Whenever the magnetic flux linked with an electric circuit changes, an emf is induced in the circuit. This is called electromagnetic induction.

8. Answer : (c) energy

Explanation: Lenz's law is a manifestation of the conservation of energy. The induced emf produces a current that opposes the change in flux, because a change in flux means a change in energy. Lenz's law is a consequence.

9. Answer : (c) magnetic field

Explanation: A magnetic field is induced in the space between the inductor. And this magnetic field corresponds to energy.

10. Answer : (a) A metal is kept in varying magnetic field

Explanation: They arise when a conductor moves through a magnetic field, or when the magnetic field surrounding a stationary conductor is varying. Summarising, we can say that anything which results in the conductor experiencing a change in the intensity or direction of a magnetic field produces eddy currents.

11. Answer : (a) electric field is produced by time varying magnetic flux

Explanation: According to Faraday's Law of electromagnetic induction, if magnetic flux through a coil changes, it leads to an induced emf across the coil. Hence, electric field is produced by time-varying magnetic fields.

12. Answer : (b) Faraday’s law

Explanation: Faraday's Law states that when the magnetic flux linking a circuit changes, an electromotive force is induced in the circuit proportional to the rate of change of the flux linkage.
This results in a moving conductor coil producing EMF.

13. Answer : (a) the induced current is produced

Explanation: When electric current is passed through the coil inside the galvanometer, induction of magnetic field takes place and thus the coil acts like a magnet which experiences torque due to permanent magnet inside galvanometer and thus the pointer is deflected.

14. Answer : (d) generator

Explanation: The law of electromagnetic induction have been used in the construction of. In a generator, emf is induced according to Lenz's rule.

15. Answer : (b) each decreases

Explanation: As the two identical coaxial circular loops carry a current i each circulating in the same direction, their flux add each other. When the two are brought closer, the total fluc linkage increase. By Lenz's a law a current will be induced in both the loops such that it opposes this change in flux. As the flux increases, the current in each loop will decreases so as to decrease the increasing flux.

16. Answer : (c) total number of magnetic field lines passing normally through given area

Explanation: Magnetic flux is a measurement of the total magnetic field which passes through a given area.The angle at which the field line intersects the area is also important. A field line passing through at a glancing angle will only contribute a small component of the field to the magnetic flux.

17. Answer : (d) it is rotated about its diameter

Explanation: An emf is induced only when magnetic flux linked with the loop changes. This is possible when the loop is rotated about a diameter.

18. Answer : (c) spark

Explanation: Eddy current circulate within the conductor.

19. Answer : (a) induced current is set up

Explanation: The angle through which the coil is deflected due to the effect of the magnetic torque is proportional to the magnitude of current in the coil.Therefore, when a coil of insulated wire which is connected to a battery, is taken to a galvanometer. Its pointer would deflect because of the production of induced current.

20. Answer : (b) Fleming’s right hand rule

Explanation: Fleming's right hand rule is used to find direction of induced current in a wire moving in a magnetic field.

21. Answer : (c) Lenz’s law

Explanation: The polarity of the induced emf or the current in any circuit is such as to oppose the cause that produces it. This is also known as Lenz's law.

22. Answer : (d) self induced e.m.f.

Explanation: The coils in resistance boxes are made from doubled insulated wire to nullify the effect of self induced e.m.f.

23. Answer : (c) 13.89 H

Explanation: PE = \(\frac{1}{2}LI^2\)

\(25\times10^{-3}=\frac{1}{2}(60\times10^{-3})^2\)

L = 13.89 H

24. Answer : (d) X-ray crystallography

Explanation: Induction furnace, galvanometer damping and speedometer of automobile are the application of eddy currents. Crystallography is done by diffraction.

25. Answer : (d) 37.5 V

Explanation:

\(e=M\frac{dI}{dt}\)

\(=\frac{0.75\times0.5}{0.01}\)

= 37.5 V

Click here to practice MCQ Question for Electromagnetic Induction Class 12

Discussion

82.	What is the frequency of AC in India?
Answer» The frequency of AC in India 50 Hz .

Discussion

83.	Explain the coil and coil experiment of Faraday.
Answer» If we replace the magnet by a current carrying coil, a similar observation can be made. When the current carrying coil is brought near the coil connected to the galvanometer, the galvanometer shows deflection indicating a current and hence an emf in the coil. Thus, the relative motion between a coil and another coil carrying current induces an emf (current).

Discussion

84.	How are the eddy currents used for damped oscillation in moving coil galvanometer?
Answer» Eddy currents are produced in soft Iron core which oppose the motion of pointer.

Discussion

85.	A coil in a magnetic field is removed with :(i) fast speed,(ii) slow speed.In which case, is the induced emf and work done more?
Answer» By the relation: The induced emf ε = \(-\frac{d \phi}{d t}\), for fast speed dt is minimum so the induced dt emf is more.

Discussion

86.	What happens to the induced emf if an iron bar is introduced into the coils in Faraday’ experiment ?
Answer» The emf increases.

Discussion

87.	What do you understand by electromagnetic induction? Write the laws of Faraday related with the electromagnetic induction and write the value of induced emf.
Answer» Michael Faraday and Joseph Henry performed experiments independently and explained that the electric field produced (induced) from time varying magnetic field can produce electric current in closed coil. This phenomenon is called electromagnetic induction. After the experiments of Henry various applications of electromagnetic induction are known. For example, the generators used at our work places to provide electric supply are based on electromagnetic induction. Electric guitars also work with the use of this phenomenon. This phenomenon is also used to melt metals fastly and safely. These days induction cookers are also popular and are replacing the traditional gas stoves. In this chapter, we will learn about the principles related to electromagnetic induction. Faraday’s Laws of Electromagnetic Induction: On the basis of Faraday’s experiments on electromagnetic induction, he gave two laws which are called Faraday’s laws electromagnetic induction. First Law: Whenever the amount of magnetic flux linked with a closed circuit changes, an emf is induced in it which lasts only so long as the change in flux is taking place. Lines of field increase - Inverse current Lines of field decrease - Direct current Second Law: According to this law, “the magnitude of induced emf is equal to the rate of change of magnetic flux.” If the induced emf is represented by ε, then mathematically, ε = \(\frac{d \phi_{B}}{d t}\) …………… (1) If N is the number of turns in coil and the turns in coil are nearby, then, the flux related to each turn uniformly changes. Thus, total induced emf, ε = \(\frac{N d \phi_{B}}{d t}\) …………… (2) Substituting ϕ_B = BA cos θ The flux in a coil can be changed by : (i) Changing the magnetic field B in coil, (ii) Changing the total area of coil or that area of the coil which is in magnetic field. For example, expanding or contracting the coil for pushing it in or drawing it out. (iii) Changing the angle between the magnetic field B and the normal of the plane of coil (or in the plane of coil). For example, rotating the coil so that initially, B is normal to the surface and then, it is along the plane.

87.

What do you understand by electromagnetic induction? Write the laws of Faraday related with the electromagnetic induction and write the value of induced emf.

Answer»

Michael Faraday and Joseph Henry performed experiments independently and explained that the electric field produced (induced) from time varying magnetic field can produce electric current in closed coil. This phenomenon is called electromagnetic induction.

After the experiments of Henry various applications of electromagnetic induction are known. For example, the generators used at our work places to provide electric supply are based on electromagnetic induction. Electric guitars also work with the use of this phenomenon. This phenomenon is also used to melt metals fastly and safely. These days induction cookers are also popular and are replacing the traditional gas stoves. In this chapter, we will learn about the principles related to electromagnetic induction.

Faraday’s Laws of Electromagnetic Induction:

On the basis of Faraday’s experiments on electromagnetic induction, he gave two laws which are called Faraday’s laws electromagnetic induction.

First Law: Whenever the amount of magnetic flux linked with a closed circuit changes, an emf is induced in it which lasts only so long as the change in flux is taking place.
Lines of field increase - Inverse current
Lines of field decrease - Direct current

Second Law: According to this law, “the magnitude of induced emf is equal to the rate of change of magnetic flux.” If the induced emf is represented by ε, then mathematically,
ε = \(\frac{d \phi_{B}}{d t}\) …………… (1)
If N is the number of turns in coil and the turns in coil are nearby, then, the flux related to each turn uniformly changes. Thus, total induced emf,
ε = \(\frac{N d \phi_{B}}{d t}\) …………… (2)
Substituting ϕ_B = BA cos θ
The flux in a coil can be changed by :
(i) Changing the magnetic field B in coil,
(ii) Changing the total area of coil or that area of the coil which is in magnetic field.
For example, expanding or contracting the coil for pushing it in or drawing it out.
(iii) Changing the angle between the magnetic field B and the normal of the plane of coil (or in the plane of coil). For example, rotating the coil so that initially, B is normal to the surface and then, it is along the plane.

Discussion

88.	Consider a closed loop C in a magnetic field (see figure). The flux passing through the loop is defined by choosing a surface whose edge coincides with the loop and using the formula φ = \(\vec{B_1}.d\vec{A_1}\) + \(\vec{B_2}.d\vec{A_2}+\) .Now if we chose two different surfaces S1 and S2 having C as their edge, would we get the same answer for flux. Justify your answer
Answer» One gets the same answer for flux. Flux can be thought of as the number of magnetic field lines passing through the surface (We draw dN = BA lines in a area ∆A perpendicular to B). As field lines of B cannot end or start in space (they form closed loops) number of lines passing through surface S₁ must be the same as the number of lines passing through the surface S₂

Discussion

89.	A circular conducting loop in a uniform magnetic field is stretched to an elongated ellipse as shown below. The magnetic field points into the page. Will an emf be induced in the loop? If so, state why and give the direction of the induced current.
Answer» Looking in the direction of the magnetic field, there will be an induced current in the clockwise sense. For the same perimeter, the area of a circle is greater than that of an ellipse. Hence, stretching the loop reduces the inward flux through its plane. To oppose this decreasing flux, a current is induced in the clockwise sense so that the field due to the induced current is into the plane of the diagram.

89.

A circular conducting loop in a uniform magnetic field is stretched to an elongated ellipse as shown below. The magnetic field points into the page. Will an emf be induced in the loop? If so, state why and give the direction of the induced current.

Answer»

Looking in the direction of the magnetic field, there will be an induced current in the clockwise sense.

For the same perimeter, the area of a circle is greater than that of an ellipse. Hence, stretching the loop reduces the inward flux through its plane. To oppose this decreasing flux, a current is induced in the clockwise sense so that the field due to the induced current is into the plane of the diagram.

Discussion

90.	In one version of Faraday’s coil-coil experiment, the two coils are wound on the same iron ring as shown, where closing and opening the switch induces a current in the other coil. How do the multiple-loop coils and iron ring enhance the observation of induced emf?
Answer» The magnetic flux through a coil is directly proportional to the number of turns a coil has. Hence, with multiloop coils in Faraday’s coil-coil experiment, the induced emf is directly proportional to N. Also, the permeability of iron being many orders of magnitude greater than air, the magnetic field lines of the primary coil P are confined to the iron ring and almost all the flux is linked with the secondary coil S. Thus, increased flux and better flux linkage enhances the magnitude of the induced emf.

Discussion

91.	Why does a galvanometer connected to a coil show deflection when a magnet is moved near it?
Answer» Moving a magnet near the coil changes the magnetic field at the coil which in turn changes the magnetic flux linked with the coil. Therefore an emf is induced in the circuit hence a current.

Discussion

92.	A 20cm long conducting rod is set into pure translation with a uniform velocity of 10cm/s perpendicular to its length. A uniform magnetic field of magnitude 0.10T exists in a direction perpendicular to the plane of motion, (a) Find the average magnetic force on the free electrons of the rod. (b) For what electric field inside the rod, the electric force on a free electron will balance the magnetic force? How is this electric field created? (c) Find the motional emf between the ends of the rod.
Answer» l = 20cm = 0.2m v = 10cm/s = 0.1m/s B = 0.10T (a) F = qvB = 1.6 × 10^–19 × 1 × 10^–1 × 1 × 10^–1 = 1.6 × 10^–21N (b) qE = qvB => E = 1 × 10^–1 × 1 × 10^–1 = 1 × 10^–2V/m This is created due to the induced emf. (c) Motional emf = Bvℓ = 0.1 × 0.1 × 0.2 = 2 × 10^–3V

92.

A 20cm long conducting rod is set into pure translation with a uniform velocity of 10cm/s perpendicular to its length. A uniform magnetic field of magnitude 0.10T exists in a direction perpendicular to the plane of motion, (a) Find the average magnetic force on the free electrons of the rod. (b) For what electric field inside the rod, the electric force on a free electron will balance the magnetic force? How is this electric field created? (c) Find the motional emf between the ends of the rod.

Answer»

l = 20cm = 0.2m

v = 10cm/s = 0.1m/s

B = 0.10T

(a) F = qvB = 1.6 × 10^–19 × 1 × 10^–1 × 1 × 10^–1 = 1.6 × 10^–21N

(b) qE = qvB

=> E = 1 × 10^–1 × 1 × 10^–1 = 1 × 10^–2V/m

This is created due to the induced emf.

(c) Motional emf = Bvℓ

= 0.1 × 0.1 × 0.2 = 2 × 10^–3V

Discussion

93.	Define the term electromagnetic induction.
Answer» The phenomena of induction of an emf in a circuit due to change in magnetic flux linked with it is called electromagnetic induction.

Discussion

94.	The mutual inductance M12 of coil 1 with respect to coil 2(a) increases when they are brought nearer.(b) depends on the current passing through the coils.(c) increases when one of them is rotated about an axis.(d) is the same as M21 of coil 2 with respect to coil 1.
Answer» (a), (d) (a) increases when they are brought nearer. (d) is the same as M₂₁ of coil 2 with respect to coil 1.

94.

The mutual inductance M12 of coil 1 with respect to coil 2(a) increases when they are brought nearer.(b) depends on the current passing through the coils.(c) increases when one of them is rotated about an axis.(d) is the same as M21 of coil 2 with respect to coil 1.

Answer»

(a), (d)

(a) increases when they are brought nearer.

(d) is the same as M₂₁ of coil 2 with respect to coil 1.

Discussion

95.	An e.m.f is produced in a coil, which is not connected to an external voltage source. This can be due to (a) the coil being in a time varying magnetic field. (b) the coil moving in a time varying magnetic field. (c) the coil moving in a constant magnetic field. (d) the coil is stationary in external spatially varying magnetic field, which does not change with time.
Answer» (a), (b), (c) (a) the coil being in a time varying magnetic field. (b) the coil moving in a time varying magnetic field. (c) the coil moving in a constant magnetic field.

95.

An e.m.f is produced in a coil, which is not connected to an external voltage source. This can be due to (a) the coil being in a time varying magnetic field. (b) the coil moving in a time varying magnetic field. (c) the coil moving in a constant magnetic field. (d) the coil is stationary in external spatially varying magnetic field, which does not change with time.

Answer»

(a), (b), (c)

(a) the coil being in a time varying magnetic field.

(b) the coil moving in a time varying magnetic field.

(c) the coil moving in a constant magnetic field.

Discussion

96.	Same as problem 4 except the coil A is made to rotate about a vertical axis (Fig 6.3). No current flows in B if A is at rest. The current in coil A, when the current in B (at t = 0) is counterclockwise and the coil A is as shown at this instant, t = 0, is (a) constant current clockwise. (b) varying current clockwise. (c) varying current counterclockwise. (d) constant current counterclockwise.
Answer» (a) constant current clockwise.

Discussion

97.	A metal plate is getting heated. It can be because(a) a direct current is passing through the plate.(b) it is placed in a time varying magnetic field.(c) it is placed in a space varying magnetic field, but does not vary with time.(d) a current (either direct or alternating) is passing through the plate.
Answer» (a), (b), (d) (a) a direct current is passing through the plate. (b) it is placed in a time varying magnetic field. (d) a current (either direct or alternating) is passing through the plate.

97.

A metal plate is getting heated. It can be because(a) a direct current is passing through the plate.(b) it is placed in a time varying magnetic field.(c) it is placed in a space varying magnetic field, but does not vary with time.(d) a current (either direct or alternating) is passing through the plate.

Answer»

(a), (b), (d)

(a) a direct current is passing through the plate.

(b) it is placed in a time varying magnetic field.

(d) a current (either direct or alternating) is passing through the plate.

Discussion

98.	If the copper disc of a pendulum swings between the poles of a magnet, the pendulum comes to rest very quickly. Explain the reason. What happens to the mechanical energy of the pendulum?
Answer» As the copper disc enters and leaves the magnetic field, the changing magnetic flux through it induces eddy current in the disc. In both cases, Fleming’s right hand rule shows that opposing magnetic force damps the motion. After a few swings, the mechanical energy becomes zero and the motion comes to a stop. Joule heating due to the eddy current warms up the disc. Thus, the mechanical energy of the pendulum is transformed into thermal energy.

98.

If the copper disc of a pendulum swings between the poles of a magnet, the pendulum comes to rest very quickly. Explain the reason. What happens to the mechanical energy of the pendulum?

Answer»

As the copper disc enters and leaves the magnetic field, the changing magnetic flux through it induces eddy current in the disc. In both cases, Fleming’s right hand rule shows that opposing magnetic force damps the motion. After a few swings, the mechanical energy becomes zero and the motion comes to a stop.

Joule heating due to the eddy current warms up the disc. Thus, the mechanical energy of the pendulum is transformed into thermal energy.

Discussion

99.	What are the values of the self-induced emf in the circuit of the previous problem at the times indicated therein?
Answer» (a) For first case at t = 100ms di/dt = 0.27 Induced emf = Ldi/dt = 1 x 0.27 = 0.27V (b) For the second case at t = 200ms di/dt = 0.036 Induced emf = Ldi/dt = 1 x 0.036 = 0.036V (c) For the third case at t = 1s di/dt = 4.1 x 10^-9V Induced emf = Ldi/dt = 4.1 x 10^-9V

99.

What are the values of the self-induced emf in the circuit of the previous problem at the times indicated therein?

Answer»

(a) For first case at t = 100ms

di/dt = 0.27

Induced emf = Ldi/dt = 1 x 0.27 = 0.27V

(b) For the second case at t = 200ms

di/dt = 0.036

Induced emf = Ldi/dt = 1 x 0.036 = 0.036V

(c) For the third case at t = 1s

di/dt = 4.1 x 10^-9V

Induced emf = Ldi/dt = 4.1 x 10^-9V

Discussion

100.

It can be shown that the mutual potential energy of two circuits is W = MI1 I2 . Therefore, the mutual inductance (M) may also be defined as the mutual potential energy (W) of two circuits corresponding to unit current flowing in each circuit.

Answer»

Mutual inductance of two magnetically linked coils equals the potential energy for unit currents in the coils.

1 H = 1 T∙m² /A (= 1 V∙s/A = 1 Ω ∙ s = 1 J/A²)

Discussion

Explore topic-wise InterviewSolutions in .

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On what factors does the magnitude of the emf induced in the circuit due to magnetic flux depend?

What is meant by wattles current?

A horizontal wire 20 m long extending from east to west is falling with a velocity of 10 m/s normal to the Earth’s magnetic field of 0.5 × 10-4 T.What is the value of induced emf in the wire?

A coil of cross sectional area 400 cm2 having 30 turns is making 1800 rev/min in a magnetic field of IT. The peak value of the induced emf is-(a) 113 V (b) 226 V (c) 339 V (d) 452 V

A plane coil of lo turns is tightly wound around a solenoid of diameter 2 cm having 400 turns per centimeter. The relative permeability of the core is 800. Calculate the mutual inductance.

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Two tightly wound solenoids have the same length and circular cross-sectional area, but the wire of solenoid 1 is half as thick as solenoid 2. The ratio of their inductances is(A) \(\cfrac14\)(B) \(\cfrac12\)(C) 2 (D) 4

A coaxial cable, whose outer radius is five times its inner radius, is carrying a current of 1.5 A. What is the magnetic field energy stored in a 2 m length of the cable ?

What are phasors?

How will you define RMS value of an alternating current?

In an AC circuit, the rms value of the current Irms , is related to the peak current I0 as-(a) Irms = \(\frac{I_0}{2}\)(b) Irms = \(\frac{I_0}{\sqrt2}\)(c) Irms = √2l0(d)Irms = πl0

Calculate the instantaneous value at 60° , average value and RMS value of an alternating current whose peak value is 20 A.

The power loss is less in transmission lines when ……

What is meant by sinusoidal alternating voltage?

AC power is transmitted from a power house at a high voltage as-(a) the rate of transmission is faster at high voltages (b) it is more economical due to less power loss (c) power cannot be transmitted at low voltages (d) a precaution against theft of transmission lines

A 40 Ω electric heater is connected to 200 V, 50 Hz main supply. The peak value of the electric current flowing in the circuit is approximately- (a) 2.5 A (b) 5 A (c) 7 A (d) 10 A

Alternating current can be measured by(a) moving coil galvanometer (b) hot wire ammeter (c) tangent galvanometer (d) none of the above

In an AC circuit with voltage V and current I, the power dissipated is-(a) VI(b) \(\frac{1}{2}\)VI(c) \(\frac{1}{\sqrt2}\) VI(d) depends on the phase difference between I and V

In an LCR circuit, the energy is dissipated in- (a) R only (b) R and L only a(c) R and C only (d) R, L and C

In a LCR AC circuit off resonance, the current- (a) is always in phase with the voltage (b) always lags behind the voltage (c) always leads the voltage (d) may lead or lag behind the voltage

A metre gauge train is heading north with speed 54 km/h in the Earth’s magnetic field 3 × 10-4 T. The emf induced across the axle joining the wheels is (A) 0.45 mV (B) 4.5 mV (C) 45 mV (D) 450 mV.

In an electric communication line, the current flows upwards. Considering the Earth’s magnetic field to be negligible, the direction of magnetic field on this electric line is:(a) Towards East(b) Towards West(c) Towards North(d) Towards South

When current in a coil changes with time, how is the back emf induced in the coil related to it?

State the steady value of the reading of the ammeter in the circuit shown below :

Class 12 Physics MCQ Questions of Electromagnetic Induction with Answers?

What is the frequency of AC in India?

Explain the coil and coil experiment of Faraday.

How are the eddy currents used for damped oscillation in moving coil galvanometer?

A coil in a magnetic field is removed with :(i) fast speed,(ii) slow speed.In which case, is the induced emf and work done more?

What happens to the induced emf if an iron bar is introduced into the coils in Faraday’ experiment ?

What do you understand by electromagnetic induction? Write the laws of Faraday related with the electromagnetic induction and write the value of induced emf.

A circular conducting loop in a uniform magnetic field is stretched to an elongated ellipse as shown below. The magnetic field points into the page. Will an emf be induced in the loop? If so, state why and give the direction of the induced current.

In one version of Faraday’s coil-coil experiment, the two coils are wound on the same iron ring as shown, where closing and opening the switch induces a current in the other coil. How do the multiple-loop coils and iron ring enhance the observation of induced emf?

Why does a galvanometer connected to a coil show deflection when a magnet is moved near it?

Define the term electromagnetic induction.

The mutual inductance M12 of coil 1 with respect to coil 2(a) increases when they are brought nearer.(b) depends on the current passing through the coils.(c) increases when one of them is rotated about an axis.(d) is the same as M21 of coil 2 with respect to coil 1.

If the copper disc of a pendulum swings between the poles of a magnet, the pendulum comes to rest very quickly. Explain the reason. What happens to the mechanical energy of the pendulum?

What are the values of the self-induced emf in the circuit of the previous problem at the times indicated therein?

It can be shown that the mutual potential energy of two circuits is W = MI1 I2 . Therefore, the mutual inductance (M) may also be defined as the mutual potential energy (W) of two circuits corresponding to unit current flowing in each circuit.