Electromagnetic Induction and Alternating Current 5 Question 1

1. A uniform but time-varying magnetic field B(t) exists in a circular region of radius a and is directed into the plane of the paper as shown. The magnitude of the induced electric field at point P at a distance r from the centre of the circular region

(2000,2M)

(a) is zero

(b) decreases as 1/r

(c) increases as r

(d) decreases as 1/r2

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Answer:

Correct Answer: 1. (b)

Solution:

Edl=dφdt=SdBdt

 or E(2πr)=πa2dBdt

For ra,

E=a22rdBdt

Induced electric field 1/r

For ra,

E(2πr)=πr2dBdt or E=r2dBdt or Er At r=a,E=a2dBdt

Therefore, variation of E with r (distance from centre) will be as follows



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