JEE Mains · Physics · STD 12 - Magnetism and matter
- JEE Mains 2025
- Hard
- MCQ

A bar magnet has total length \(2 l=20\) units and the field point \(P\) is at a distance \(\mathrm{d}=10\) units from the centre of the magnet. If the relative uncertainty of length measurement is \(1 \%\), then uncertainty of the magnetic field at point P is :
Pick an option to check your answer.
Answer & Solution
Correct Answer
(A) \(4 \%\)
Step-by-step Solution
Detailed explanation

Magnetic field at \(P, B=\frac{\mu_0}{4 \pi} \frac{m(2 l)}{r^3}\), where \(m\) is the pole strength
\(\begin{aligned}
\Rightarrow\left(\frac{\Delta B}{B} \times 100\right) & =\left(\frac{\Delta l}{l}\right) \times 100+3\left|\frac{\Delta r}{r}\right| \times 100 \\
& =1 \%+3 \%=4 \%
\end{aligned}\)
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