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Physics · 2025 · 3 marks
CBSE 2025 · Region 6 · Set 3 · Q24
A rectangular loop carries a current of 1 A. A straight long wire carrying 2 A current is kept near the loop in the same plane as shown in the…
A rectangular loop carries a current of $\displaystyle 1$ A . A straight long wire carrying $\displaystyle 2$ A current is kept near the loop in the same plane as shown in the figure.
Find :
(i)
the torque acting on the loop, and
(ii)
the magnitude and direction of the net force on the loop.
Marking-scheme solution
(i)
$\displaystyle \tau = mB\sin\theta$
As $\displaystyle \vec{m}$ and $\displaystyle \vec{B}$ are in same direction, $\displaystyle \theta = 0^{0}$
$\displaystyle \tau = 0$
(ii)
$\displaystyle F = \dfrac{\mu_0 I_1 I_2 l}{2\pi r}$
$\displaystyle F_{net} = \dfrac{\mu_0 I_1 I_2 l}{2\pi}\left(\dfrac{1}{r_1} - \dfrac{1}{r_2}\right)$
$\displaystyle = \dfrac{4\pi \times 10^{-7} \times 2 \times 1 \times 5 \times 10^{-2}}{2\pi \times 10^{-2}}\left(1 - \dfrac{1}{2}\right)$
$\displaystyle F_{net} = 1 \times 10^{-6}\ \text{N}$
Net force on the loop is towards the long straight wire.
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CBSE Class 12 Physics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.