JEE Main 2025 — Magnetic Effects of Current Question with Solution
JEE Main 2025 (24 Jan Shift 2)
Question
A tightly wound long solenoid carries a current of 1.5 A . An electron is executing uniform circular motion inside the solenoid with a time period of 75 ns . The number of turns per metre in the solenoid is -.
[Take mass of electron , charge of electron ,
Enter your answer
Show full solutionCorrect answer: 250
Correct answer
250
Step-by-step explanation
Since time period of a revolving charge is
Where magnetic field
due to a solenoid
$\begin{aligned}
& \therefore \mathrm{T}=\frac{2 \pi \mathrm{~m}}{\mathrm{q}\left(\mu_0 \mathrm{nI}\right)} \\
& 75 \times 10^{-9}=\frac{(2 \pi)\left(9 \times 10^{-31}\right)}{1.6 \times 10^{-19} \times 4 \pi \times 10^{-7} \times \mathrm{n} \times 1.5} \\
& \mathrm{~N}=250
\end{aligned}$
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This is a previous-year question from JEE Main 2025, covering the Magnetic Effects of Current chapter of Physics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.