Doubtclip is an AI tutor that turns any homework or exam doubt into a step-by-step whiteboard video lesson with diagrams, formulas, and voice explanation.

Which subjects and exams does it support?

It supports Physics, Chemistry, Mathematics/Calculus and related STEM doubts for school boards, JEE, NEET, and global high-school / undergrad practice.

How do I get a video solution?

Upload a photo of the question or paste the text, sign in, and Doubtclip generates a whiteboard-style explanation video you can watch and share.

Is Doubtclip available worldwide?

Yes. Doubtclip is a web app for students globally. Lessons are available in English and Hinglish.

Electromagnetic Induction

JEE Main level, single correct, medium

95 of 153

Question 95 of 153

A thin strip $10cm$ long is on a $U$ shaped wire of negligible resistance and it is connected to a spring of spring constant $0.5N{m}^{-1}$ (see figure). The assembly is kept in a uniform magnetic field of $0.1T.$ If the strip is pulled from its equilibrium position and released, the number of oscillations it performs before its amplitude decreases by a factor of $e$ is $N$ . If the mass of the strip is $50$ grams, its resistance $10\Omega$ and air drag negligible, $N$ will be close to:

Show answer and solution

Answer: (B) $5000$

Equation of motion for slider:

-m\dfrac{{d}^{2}x}{d{t}^{2}}=kx+ilB

m\dfrac{{d}^{2}x}{d{t}^{2}}+kx+\left(\dfrac{Blv}{R}\right)lB=0\Rightarrow m\dfrac{{d}^{2}x}{d{t}^{2}}+\dfrac{{B}^{2}{l}^{2}}{R}.\dfrac{dx}{dt}+kx=0

Comparing with

m\dfrac{{d}^{2}x}{d{t}^{2}}+b.\dfrac{dx}{dt}+kx=0

m=m;b=\dfrac{{B}^{2}{l}^{2}}{R};k=k

We know:

A={A}_{0}{e}^{\dfrac{-b}{2m}\times t}={A}_{0}{e}^{-\dfrac{{B}^{2}{l}^{2}}{2mR}\times t}

For amplitude to be

{A}_{0}/e,

{A}_{0}{e}^{-\dfrac{{B}^{2}{l}^{2}}{2mR}\times t}=\dfrac{A}{e}\Rightarrow \dfrac{{B}^{2}{l}^{2}}{2mR}\times t=1

t=\dfrac{2mR}{{B}^{2}{l}^{2}}=10,000sec

Time period =

2\pi \sqrt{\dfrac{m}{k}}=2s

Number of oscillations =

\dfrac{10,000}{2}=5,000

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.

See it move: Electromagnetic induction simulationDrag the sliders and watch the numbers in this question change.

More Physics practice

JEE Main Physics practice question on Electromagnetic Induction (Motional and Rotational EMF), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.