Exam

JEE Main

Year

2025

Date

28 January

Shift

Evening Shift

Subject

Physics

Chapter

Magnetic Properties of Matter

JEE Main 2025 · 28 January · Evening Shift · Physics · Magnetic Properties of Matter

A bar magnet has total length 2 l=20 units and the field point P is...

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 :

Step-by-step solution

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