JEE Main 2022 · 26 Jul · Shift 2 · Physics Q46

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PhysicsSingle correct+4 / -1Question 46 of 90

Two concentric circular loops of radii $r_1$ = 30 cm and $r_2$ = 50 cm are placed in X-Y plane as shown in the figure. A current I = 7 A is flowing through them in the direction as shown in figure. The net magnetic moment of this system of two circular loops is approximately :

Two concentric circles of radii r1 (inner) and r2 (outer); current I is anticlockwise in the inner loop and clockwise in the outer loop.

\dfrac72\hat k

^2

-\dfrac72\hat k

^2

7\hat k

^2

-7\hat k

^2

Answer and worked solution

Official answer: B

Opposite currents, so the moments subtract: $I\pi\left(r_2^2-r_1^2\right)=7\pi(0.25-0.09)\approx3.5$ A m².

Direction. The larger (outer) loop's current is clockwise in the figure, so the net moment is along $-\hat k$ : $-\frac72\hat k$ A m².

(B)

Topics:Torque on a current loop

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JEE Main 2022 · 26 Jul · Shift 2, Physics question 46