Faraday's law, induced emf, Lenz's law and eddy currents — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Faraday's law states that induced emf equals

• A. the negative time rate of change of magnetic flux linkage
• B. magnetic flux itself
• C. current divided by resistance only
• D. the rate of change of electric charge regardless of flux

Question 2 · difficulty L1 · understanding

Lenz's law determines the direction of induced current by requiring that it

• A. always reinforces the external flux
• B. opposes the change in magnetic flux that produces it
• C. always flows clockwise
• D. depends only on wire resistance

Question 3 · difficulty L2 · understanding

A single loop experiences its magnetic flux changing uniformly from 0.20 Wb to 0.50 Wb in 0.10 s. The emf magnitude is

• A. 0.3 V
• B. 7.0 V
• C. 3.0 V
• D. 0.03 V

Question 4 · difficulty L2 · application

A 100-turn coil has flux per turn changing at 2×10^-4 Wb s^-1. The induced emf magnitude is

• A. 2×10^-4 V
• B. 2.0 V
• C. 50 V
• D. 0.020 V

Question 5 · difficulty L2 · understanding

A square loop of side 2 cm is placed in a time varying magnetic field with magnitude as $B=0.4 \sin (300 t)$ Tesla. The normal to the plane of loop makes an angle of $60^{\circ}$ with the field. The maximum induced emf produced in the loop is $\_\_\_\_$ mV .

• A. 12
• B. 18
• C. 21
• D. 24

Question 6 · difficulty L2 · understanding

A circular loop of radius 7 cm is placed in uniform magnetic field of 0.2 T directed perpendicular to plane of loop. The loop is converted into a square loop in 0.5 s . The EMF induced in the loop is $\_\_\_\_$ mV.

• A. 13.2
• B. 6.6
• C. 1.32
• D. 8.25

Question 7 · difficulty L2 · understanding

A 20 m long uniform copper wire held horizontally is allowed to fall under the gravity $\left(g=10 \mathrm{~m} / \mathrm{s}^2\right)$ through a uniform horizontal magnetic field of 0.5 Gauss perpendicular to the length of the wire. The induced EMF across the wire when it travells a vertical distance of 200 m is $\_\_\_\_$ mV .

• A. $200 \sqrt{10}$
• B. $0.2 \sqrt{10}$
• C. $20 \sqrt{10}$
• D. $2 \sqrt{10}$

Question 8 · difficulty L2 · understanding

A uniform magnetic field of 0.4 T acts perpendicular to a circular copper disc 20 cm in radius. The disc is having a uniform angular velocity of 10 $\pi$ rad s -1 about an axis through its centre and perpendicular to the disc. What is the potential difference developed between the axis of the disc and the rim? $(\pi=3.14)$

• A. 0.5024 V
• B. 0.0628 V
• C. 0.2512 V
• D. 0.1256 V

Question 9 · difficulty L2 · understanding

A coil is places perpendicular to a magnetic field of $$5000 \mathrm{~T}$$. When the field is changed to $$3000 \mathrm{~T}$$ in $$2 \mathrm{~s}$$, an induced emf of $$22 \mathrm{~V}$$ is produced in the coil. If the diameter of the coil is $$0.02 \mathrm{~m}$$, then the number of turns in the coil is:

• A. 35
• B. 70
• C. 7
• D. 140

Question 10 · difficulty L2 · understanding

Match List I with List II List I List II (A) Gauss's law of magnetostatics (I) $$\oint \vec{E} \cdot \vec{d} a=\frac{1}{\varepsilon_0} \int \rho d V$$ (B) Faraday's law of electro magnetic induction (II) $$\oint \vec{B} \cdot \vec{d} a=0$$ (C) Ampere's law (III) $$\int \vec{E} \cdot \vec{d} l=\frac{-d}{d t} \int \vec{B} \cdot \vec{d} a$$ (D) Gauss's law of electrostatics (IV) $$\oint \vec{B} \cdot \vec{d} l=\mu_0 I$$ Choose the correct answer from the options given below:

• A. A-III, B-IV, C-I, D-II
• B. A-IV, B-II, C-III, D-I
• C. A-II, B-III, C-IV, D-I
• D. A-I, B-III, C-IV, D-II