Q: The magnetic flux through a plane surface of area A in a uniform field B, the normal making angle \theta with the field, is:

BA\cos\theta. Flux is the scalar product \vec{B}\cdot\vec{A}, greatest when the surface is perpendicular to the field.

Q: One weber is equivalent to:

1\text{ T}\cdot\text{m}^2. It is also one volt second, since an EMF of one volt corresponds to flux changing at one weber per second.

Q: The flux linked with a coil changes from 0.8\text{ Wb} to 0.2\text{ Wb} in 0.1\text{ s}. The induced EMF is:

6\text{ V}. |e| = \left|\dfrac{\Delta\Phi}{\Delta t}\right| = \dfrac{0.8 - 0.2}{0.1} = 6\text{ V}.

Q: A coil of 100 turns has flux changing at 0.02\text{ Wb}/\text{s}. The induced EMF is:

2\text{ V}. e = N\dfrac{d\Phi}{dt} = 100 \times 0.02 = 2\text{ V}.

Q: A coil of area 0.02\text{ m}^2 lies perpendicular to a field of 0.5\text{ T}. The flux through it is:

0.01\text{ Wb}. \Phi = BA\cos 0^\circ = 0.5 \times 0.02 = 0.01\text{ Wb}.

Q: A coil of area 0.04\text{ m}^2 lies with its plane perpendicular to a field of 0.3\text{ T}. The flux through it is:

0.012\text{ Wb}. \Phi = BA = 0.3 \times 0.04 = 0.012\text{ Wb}.

Question 1

The magnetic flux through a plane surface of area A in a uniform field B, the normal making angle 	heta with the field, is:

Accepted Answer

BA\cos	heta. Flux is the scalar product \vec{B}\cdot\vec{A}, greatest when the surface is perpendicular to the field.

Question 2

Faraday's first law of electromagnetic induction states that:

Accepted Answer

An EMF is induced in a circuit whenever the magnetic flux linked with it changes. It is the change of flux, not its magnitude, that matters; a steady flux however large induces nothing.

Question 3

Faraday's second law gives the magnitude of the induced EMF in a coil of N turns as:

Accepted Answer

e = -N\dfrac{d\Phi}{dt}. The minus sign expresses Lenz's law: the induced EMF opposes the change producing it.

Question 4

One weber is equivalent to:

Accepted Answer

1	ext{ T}\cdot	ext{m}^2. It is also one volt second, since an EMF of one volt corresponds to flux changing at one weber per second.

Question 5

The flux linked with a coil changes from 0.8	ext{ Wb} to 0.2	ext{ Wb} in 0.1	ext{ s}. The induced EMF is:

Accepted Answer

6	ext{ V}. |e| = \left|\dfrac{\Delta\Phi}{\Delta t}ight| = \dfrac{0.8 - 0.2}{0.1} = 6	ext{ V}.

Question 6

A coil of 100 turns has flux changing at 0.02	ext{ Wb}/	ext{s}. The induced EMF is:

Accepted Answer

2	ext{ V}. e = N\dfrac{d\Phi}{dt} = 100 	imes 0.02 = 2	ext{ V}.

Question 7

A coil of area 0.02	ext{ m}^2 lies perpendicular to a field of 0.5	ext{ T}. The flux through it is:

Accepted Answer

0.01	ext{ Wb}. \Phi = BA\cos 0^\circ = 0.5 	imes 0.02 = 0.01	ext{ Wb}.

Question 8

A coil of area 0.04	ext{ m}^2 lies with its plane perpendicular to a field of 0.3	ext{ T}. The flux through it is:

Accepted Answer

0.012	ext{ Wb}. \Phi = BA = 0.3 	imes 0.04 = 0.012	ext{ Wb}.

Question 9

Lenz's law states that the induced current flows in such a direction as to:

Accepted Answer

Oppose the change in flux that produces it. This is what the negative sign in e = -N\dfrac{d\Phi}{dt} represents.

Question 10

The direction of the current induced in a straight conductor moving in a magnetic field is given by:

Accepted Answer

Fleming's right-hand rule. Fleming's left-hand rule applies to the force on a current; the right-hand rule applies to induced current.

Question 11

If the flux through a coil is increasing, the induced current in the coil flows so as to:

Accepted Answer

Set up a flux opposing the increase. Opposition to an increase means the induced flux points opposite to the original.

Question 12

An induced EMF of 6	ext{ V} acts in a circuit of resistance 3\,\Omega. The induced current is:

Accepted Answer

2	ext{ A}. I = \dfrac{e}{R} = \dfrac{6}{3} = 2	ext{ A}.

Question 13

A coil of resistance 4\,\Omega has an induced EMF of 8	ext{ V}. The induced current is:

Accepted Answer

2	ext{ A}. I = \dfrac{8}{4} = 2	ext{ A}.

Question 14

If the same flux change occurs in half the time, the induced EMF becomes:

Accepted Answer

Twice as large. e \propto \dfrac{1}{\Delta t} for a given \Delta\Phi.

Question 15

If the magnetic field through a coil is doubled over the same time interval, the induced EMF:

Accepted Answer

Doubles. The flux change doubles while the time is unchanged, so the EMF doubles.

Question 16

A straight conductor of length l moves with velocity v perpendicular to a field B. The EMF induced across it is:

Accepted Answer

Blv. In one second the rod sweeps an area lv, so the flux cut per second is Blv.

Question 17

The direction of the motional EMF in a moving conductor is found using:

Accepted Answer

Fleming's right-hand rule. With the forefinger along the field and the thumb along the motion, the middle finger gives the induced current.

Question 18

A rod of length 0.2	ext{ m} moves at 10	ext{ m/s} perpendicular to a field of 0.5	ext{ T}. The EMF induced is:

Accepted Answer

1	ext{ V}. e = Blv = 0.5 	imes 0.2 	imes 10 = 1	ext{ V}.

Question 19

A rod of length 1	ext{ m} moves at 5	ext{ m/s} perpendicular to a field of 0.2	ext{ T}. The EMF induced is:

Accepted Answer

1	ext{ V}. e = Blv = 0.2 	imes 1 	imes 5 = 1	ext{ V}.

Question 20

If the speed of a rod moving in a magnetic field is doubled, the motional EMF:

Accepted Answer

Doubles. e = Blv \propto v.

Electromagnetic Induction — MH-CET Physics MCQs with Solutions

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Sample questions with solutions