NEET 2016 Phase 2 · PhysicsFaraday lawPrevious Year Question
A uniform magnetic field is restricted within a region of radius r. The magnetic field changes with time at a rate dB/dt. Loop 1 of radius R > r encloses the region r and loop 2 of radius R is outside the region of magnetic field as shown in the figure below. Then the e.m.f. generated is
Answer: (D) -(dB/dt)πr² in loop 1 and zero in loop 2. Answer: (d) Solution: By Faraday's law, induced emf = −dΦ/dt, and Φ is the flux actually enclosed by the loop.
- A.Zero in loop 1 and zero in loop 2
- B.-(dB/dt)πr² in loop 1 and -(dB/dt)πr² in loop 2
- C.-(dB/dt)πR² in loop 1 and zero in loop 2
- D.-(dB/dt)πr² in loop 1 and zero in loop 2✓
Correct Answer
(D) -(dB/dt)πr² in loop 1 and zero in loop 2
Solution & Explanation
Answer: (d) Solution: By Faraday's law, induced emf = −dΦ/dt, and Φ is the flux actually enclosed by the loop. Loop 1 (R > r) encloses the entire field region of radius r, so Φ = B·πr² and emf = −(dB/dt)πr² (it depends on the field's area πr², not the loop area). Loop 2 lies entirely outside the field region, so it encloses zero flux and its emf = 0. Hence −(dB/dt)πr² in loop 1 and zero in loop 2 → answer D.
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