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JEE MAIN 2019
08-04-2019 S1
Question
A circular coil having $N$ turns and radius $r$ carries a current I. It is held in the XZ plane in a magnetic field $B \hat{i}$. The torque on the coil due to the magnetic field is:
Select the correct option:
A
$\frac{B \pi r^2 \mid}{N}$
B
$\frac{\mathrm{Br}^2 \mid}{\pi \mathrm{N}}$
C
$\mathrm{B} \pi \mathrm{r}^2 \mathrm{I} \mathrm{N}$
D
Zero
✓ Correct! Well done.
✗ Incorrect. Try again or view the solution.
Solution
$\begin{aligned}|\vec{\tau}| & =|\vec{\mu} \times \vec{B}| \\ & =N I A \times B[A=\pi r 2] \\ \Rightarrow \tau & =N I \pi r^2 B\end{aligned}$
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