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JEE Main 201419 AprilOnline
Exam
JEE Main
Year
2014
Date
19 April
Mode
Online
Subject
Physics
Chapter
Electromagnetic Induction

JEE Main 2014 · 19 April · Online · Physics · Electromagnetic Induction

A square frame of side 10cm and a long straight wire carrying...

A square frame of side 10cm10cm and a long straight wire carrying current 1A1A are in the plane of the paper. Starting from close to the wire, the frame moves towards the right with a constant speed of 10ms−110m{s}^{- 1} (see figure). The e.m.f induced at the time the left arm of the frame is at x=10cmx = 10cm from the wire is

A square frame of side 10cm and a long straight wire carrying current 1A are in the plane of the paper. Starting from

Options

  1. A0.75μV0.75\mu V
  2. B1\muV1\muV
  3. C2\muV2\muV
  4. D0.5μV0.5\mu V

Correct answer

B. 1\muV1\muV

Step-by-step solution

A square frame of side 10cm and a long straight wire carrying current 1A are in the plane of the paper. Starting from

dϕ=μ0i2\piyadydϕ = \dfrac{{\mu}_{0}i}{2\piy}ady

ϕ=μ0ia2π∫xx+adyy=μ0ia2π[ln⁡(x+a)−ln⁡x]ϕ = \dfrac{{\mu}_{0}ia}{2\pi}\mathop{∫}_{x}^{x + a}\dfrac{dy}{y} = \dfrac{{\mu}_{0}ia}{2\pi}\left[\ln \left(x + a\right) - \ln x\right]

E.m.f=−dϕdt=−μ0ia2π[1x+adxdt−1xdxdt]\text{E.m.f} =- \dfrac{dϕ}{dt} = - \dfrac{{\mu}_{0}ia}{2\pi}\left[\dfrac{1}{x + a}\dfrac{dx}{dt} - \dfrac{1}{x}\dfrac{dx}{dt}\right]

=μ0ia2πa.vx(x+a)=μ02π.ia2vx(x+a)=2×10−7×1×(0.12×10)0.1×0.2=1\muV= \dfrac{{\mu}_{0}ia}{2\pi}\dfrac{a . v}{x\left(x + a\right)} = \dfrac{{\mu}_{0}}{2\pi} . \dfrac{i{a}^{2}v}{x\left(x + a\right)} = 2 \times {10}^{- 7} \times \dfrac{1 \times \left({0.1}^{2} \times 10\right)}{0.1 \times 0.2} = 1\muV

Alternative method:

Consider two sides which are perpendicular to the velocity as case of motional e.m.f.

A square frame of side 10cm and a long straight wire carrying current 1A are in the plane of the paper. Starting from

E=E1−E2=(B1–B2)VlE = {E}_{1} - {E}_{2} = \left({B}_{1} – {B}_{2}\right)Vl

=μ0I2π(1x−1x+a)Vl= \dfrac{{\mu}_{0}I}{2\pi}\left(\dfrac{1}{x} - \dfrac{1}{x + a}\right)Vl

=2×10−7×1(10.1−10.2)×10×0.1= 2 \times {10}^{- 7} \times 1\left(\dfrac{1}{0.1} - \dfrac{1}{0.2}\right) \times 10 \times 0.1

=10−6V=1\muV= {10}^{- 6}V = 1\muV

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