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Electric Charges and Fields
Question
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A conducting circular loop is placed in uniform magnetic field 0.04 T with its plane perpendicular to the magnetic field. The radius of the loop starts shrinking at 2 mms-1. The induced emf in the loop when the radius is 2 cm is 

  • 3.2 π μ V

  • 4.8 π μ V

  • 0.8 π μ V

  • 1.6 π μ V

Answer

A.

3.2 π μ V

According to faraday's second law of electromagnetic induction the induced emf is given by rate of change of magnetic flux linked with the circuit.
Here, B = 0.04 T and -dr /dt = 2 mms-1
Induced emf, e = dΦ / dt = -BdA/dt = -Bd(πr2)/dt
=- Bπ 2r dr / dt
now, if r = 2 cm
e  = -0.04 x π x 2 x 2 x 10-2 x2 x 10-3
3.2 π μ V

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Some More Questions From Electric Charges and Fields Chapter

a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?
b) Explain why two field lines never cross each other at any point? 

Figure shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?