Electromagnetic Induction Chapter-Wise Test 9

Correct answer Carries: 4.

Wrong Answer Carries: -1.

A conducting rod moves parallel to its length in a uniform magnetic field. Why is no emf induced across its ends?

Motional emf requires the rod to move perpendicular to the magnetic field to cut flux lines. Moving parallel to its length does not change the flux through any area, so no emf is induced.

Due to high resistance
Due to low magnetic field strength
Due to high velocity
Due to no flux cutting
4

A loop moves into a 0.3 T field at 1 m/s. If the length perpendicular to velocity is 0.1 m, how long does the emf last?

Time = distance/velocity, where distance = width of loop along motion.

Assume width = 0.1 m (typical NEET assumption).

\( t = \frac{0.1}{1} = 0.1 \, \text{s} \).

0.05 s
0.1 s
0.15 s
0.2 s
2

A solenoid with mutual inductance 0.3 H has a current change of 6 A/s in the primary coil. What is the induced emf in the secondary coil?

\( \varepsilon = M \frac{dI}{dt} = 0.3 \times 6 = 1.8 \, \text{V} \).

1.2 V
1.5 V
1.8 V
2.0 V
3

A coil is placed in a time-varying magnetic field. The direction of the induced current is determined by which principle?

Lenz’s law dictates that the induced current opposes the change in magnetic flux, determining its direction based on the field’s variation.

Lenz’s law
Ohm’s law
Coulomb’s law
Biot-Savart law
1

A bar magnet is pushed towards a coil with its north pole first, then pulled back. The direction of the induced current in the coil during withdrawal is opposite to that during approach due to what?

Lenz’s law causes the current to oppose the flux change: it creates a north pole to repel the approaching magnet and a south pole to attract it during withdrawal, reversing the direction.

Faraday’s law
Ampere’s law
Lenz’s law
Ohm’s law
3

A rod of length 0.25 m moves at 3 m/s in a 0.4 T field perpendicular to its length. What is the induced emf?

\( \varepsilon = B l v = 0.4 \times 0.25 \times 3 = 0.3 \, \text{V} \).

0.3 V
0.35 V
0.4 V
0.45 V
1

A coil of 120 turns and area 0.025 m² is in a field that decreases from 0.08 T to 0 in 0.4 s. What is the induced emf?

\( \Delta \Phi = B A = 0.08 \times 0.025 = 0.002 \, \text{Wb} \).

\( \varepsilon = N \frac{\Delta \Phi}{\Delta t} = 120 \times \frac{0.002}{0.4} = 120 \times 0.005 = 0.6 \, \text{V} \).

0.4 V
0.6 V
0.8 V
1.0 V
2

A coil of 140 turns and area 0.05 m² is in a 0.1 T field that drops to zero in 0.25 s. What is the induced emf?

\( \Delta \Phi = B A = 0.1 \times 0.05 = 0.005 \, \text{Wb} \).

\( \varepsilon = N \frac{\Delta \Phi}{\Delta t} = 140 \times \frac{0.005}{0.25} = 140 \times 0.02 = 2.8 \, \text{V} \).

2.0 V
2.5 V
2.8 V
3.0 V
3

A rectangular loop of 0.18 m × 0.3 m moves out of a 0.25 T field at 1 m/s along its shorter side. What is the emf?

\( \varepsilon = B l v \), \( l = 0.3 \, \text{m} \).

\( \varepsilon = 0.25 \times 0.3 \times 1 = 0.075 \, \text{V} \).

0.05 V
0.06 V
0.07 V
0.075 V
4

In an AC generator, the frequency of the output voltage depends on which factor?

The frequency equals the rotational speed of the coil in revolutions per second, as each full rotation produces one cycle of emf (\( f = \frac{\omega}{2\pi} \)).

Magnetic field strength
Coil area
Number of turns
Rotational speed of the coil
4

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