back to directory
NEET PHYSICSMAGNETISM AND MATTERMedium

Question

A 250-turn rectangular coil with a length of 2.1 cm2.1 \text{ cm} and a width of 1.25 cm1.25 \text{ cm} carries a current of 85 μA85 \text{ }\mu\text{A} and is subjected to a magnetic field of strength 0.85 T0.85 \text{ T}. What is the work done to rotate the coil by 180∘180^\circ against the torque?

A

9.1 μ\muJ

B

4.55 μ\muJ

C

2.3 μ\muJ

D

1.5 μ\muJ

Step-by-Step Solution

  1. Magnetic Moment (mm): The current-carrying coil behaves as a magnetic dipole. The magnetic moment is given by m=NIAm = NIA, where NN is the number of turns, II is the current, and AA is the area of the coil.
  • N=250N = 250
  • I=85 μA=85×10−6 AI = 85 \text{ }\mu\text{A} = 85 \times 10^{-6} \text{ A}
  • A=length×width=(2.1×10−2 m)×(1.25×10−2 m)≈2.625×10−4 m2A = \text{length} \times \text{width} = (2.1 \times 10^{-2} \text{ m}) \times (1.25 \times 10^{-2} \text{ m}) \approx 2.625 \times 10^{-4} \text{ m}^2 m=250×(85×10−6)×(2.625×10−4)≈5.58×10−6 A m2m = 250 \times (85 \times 10^{-6}) \times (2.625 \times 10^{-4}) \approx 5.58 \times 10^{-6} \text{ A m}^2

  1. Work Done (WW): The work done to rotate a magnetic dipole in a uniform magnetic field BB from an initial angle θ1\theta_1 to a final angle θ2\theta_2 is equal to the change in potential energy (U=−mBcos⁡θU = -mB \cos \theta). Rotating 'against the torque' typically implies moving from the stable equilibrium (θ1=0∘\theta_1 = 0^\circ) to the unstable equilibrium (θ2=180∘\theta_2 = 180^\circ). W=Uf−Ui=−mB(cos⁡180∘−cos⁡0∘)W = U_f - U_i = -mB(\cos 180^\circ - \cos 0^\circ) W=−mB(−1−1)=2mBW = -mB(-1 - 1) = 2mB

  2. Calculation: W=2×(5.58×10−6)×0.85W = 2 \times (5.58 \times 10^{-6}) \times 0.85 W≈9.48×10−6 J=9.48 μJW \approx 9.48 \times 10^{-6} \text{ J} = 9.48 \text{ }\mu\text{J} The calculated value (9.48 μJ9.48 \text{ }\mu\text{J}) is closest to the option 9.1 μJ9.1 \text{ }\mu\text{J}. (Discrepancy likely due to rounding of area dimensions in the original question source).

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from MAGNETISM AND MATTER. 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.

PHYSICSMAGNETISM AND MATTERrectangularlengthcarriescurrentmutexta

More MAGNETISM AND MATTER Questions

View all

If a diamagnetic substance is brought near the north or the south pole of a bar magnet, it is

A.repelled by both the poles
B.repelled by the north pole and attracted by the south pole
C.attracted by the north pole and repelled by the south pole
D.attracted by both the poles
EasySolve

The variation of susceptibility ($\chi$) with absolute temperature ($T$) for a paramagnetic material is represented as:

A.Option 1
B.Option 2
C.Option 3
D.Option 4
EasySolve

If $\theta_1$ and $\theta_2$ be the apparent angles of dip observed in two vertical planes at right angles to each other, then the true angle of dip $\theta$ is given by:

A.$\cot^2 \theta = \cot^2 \theta_1 + \cot^2 \theta_2$
B.$\tan^2 \theta = \tan^2 \theta_1 + \tan^2 \theta_2$
C.$\cot^2 \theta = \cot^2 \theta_1 - \tan^2 \theta_2$
D.$\tan^2 \theta = \tan^2 \theta_1 - \tan^2 \theta_2$
MediumSolve

A magnetic needle suspended parallel to a magnetic field requires $\sqrt{3}$ J of work to turn it through $60^\circ$. The torque needed to maintain the needle in this position will be:

A.$2\sqrt{3}$ J
B.3 J
C.$\sqrt{3}$ J
D.$\frac{3}{2}$ J
MediumSolve

An iron bar of length $L$ has a magnetic moment $M$. It is bent at the middle of its length such that the two arms make an angle $60^{\circ}$ with each other. The magnetic moment of this new magnet is:

A.M/2
B.2M
C.M\sqrt{3}
D.M
MediumSolve

Above Curie temperature:

A.a ferromagnetic substance becomes paramagnetic.
B.a paramagnetic substance becomes diamagnetic.
C.a diamagnetic substance becomes paramagnetic.
D.a paramagnetic substance becomes ferromagnetic.
EasySolve

The magnetic susceptibility is negative for:

A.paramagnetic material only.
B.ferromagnetic material only.
C.paramagnetic and ferromagnetic materials.
D.diamagnetic material only.
EasySolve

The following figures show the arrangement of bar magnets in different configurations. Each magnet has a magnetic dipole moment $\mathbf{m}$. Which configuration has the highest net magnetic dipole moment?

A.Option 1
B.Option 2
C.Option 3
D.Option 4
EasySolve

Why 32,000+ students choose TopperSquare

Everything you need to crack NEET

15,000+ Chapter MCQs

Physics, Chemistry, Biology — chapter-wise, topic-wise practice

AI Performance Analytics

Know your weak topics. Get a personalised study plan.

Full NEET Mock Tests

180 questions, timed, with detailed score analysis

PYQ Sets 2010–2024

15 years of past papers with solved explanations

Start Practising Free

No credit card · 30-second signup · Free forever plan included

This neet physics practice question is part of the TopperSquare free question bank. TopperSquare offers 15,000+ chapter-wise NEET MCQs across Physics, Chemistry, and Biology with detailed step-by-step explanations, full mock tests, NEET PYQs (2010–2024), and an AI-powered performance analytics dashboard. browse all neet practice questions → · practice physics sets →

Explore more subjects:Physics MCQs•Chemistry MCQs•Biology MCQs•Botany MCQs•Zoology MCQs•NEET Mock Tests•NEET PYQs