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NEET PHYSICSELECTROMAGNETIC INDUCTIONMedium

Question

A conducting square frame of side aa and a long straight wire carrying current II are located in the same plane as shown in the figure. The frame moves to the right with a constant velocity vv. The emf induced in the frame will be proportional to:

A

1x2\frac{1}{x^2}

B

1(2xa)2\frac{1}{(2x-a)^2}

C

1(2x+a)2\frac{1}{(2x+a)^2}

D

1(2xa)(2x+a)\frac{1}{(2x-a)(2x+a)}

Step-by-Step Solution

  1. Magnetic Field: The magnetic field BB at a distance rr from a long straight wire carrying current II is given by B=μ0I2πrB = \frac{\mu_0 I}{2\pi r} .
  2. Motional EMF: A conductor of length LL moving with velocity vv perpendicular to a magnetic field BB induces an emf ε=BLv\varepsilon = B L v .
  3. Setup: The square frame of side aa has two vertical sides moving perpendicular to the magnetic field lines. Let xx be the distance of the center of the frame from the wire. The near side is at distance r1=xa2=2xa2r_1 = x - \frac{a}{2} = \frac{2x-a}{2}. The far side is at distance r2=x+a2=2x+a2r_2 = x + \frac{a}{2} = \frac{2x+a}{2}.
  4. Induced EMF: EMF in near side: ε1=μ0I2πr1av=μ0Iavπ(2xa)\varepsilon_1 = \frac{\mu_0 I}{2\pi r_1} a v = \frac{\mu_0 I a v}{\pi (2x-a)}. EMF in far side: ε2=μ0I2πr2av=μ0Iavπ(2x+a)\varepsilon_2 = \frac{\mu_0 I}{2\pi r_2} a v = \frac{\mu_0 I a v}{\pi (2x+a)}.
  5. Net EMF: Since the magnetic field decreases with distance, ε1>ε2\varepsilon_1 > \varepsilon_2. The induced emfs in the two sides oppose each other in the loop loop (Lenz's Law). Thus, the net emf is: εnet=ε1ε2(12xa12x+a)\varepsilon_{net} = \varepsilon_1 - \varepsilon_2 \propto \left( \frac{1}{2x-a} - \frac{1}{2x+a} \right) εnet(2x+a)(2xa)(2xa)(2x+a)\varepsilon_{net} \propto \frac{(2x+a) - (2x-a)}{(2x-a)(2x+a)} εnet2a(2xa)(2x+a)\varepsilon_{net} \propto \frac{2a}{(2x-a)(2x+a)} Therefore, the induced emf is proportional to 1(2xa)(2x+a)\frac{1}{(2x-a)(2x+a)}.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from ELECTROMAGNETIC INDUCTION. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSELECTROMAGNETIC INDUCTIONconductingsquarestraightcarryingcurrent

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