JEE Main 2022 · 25 Jul · Shift 2 · Physics Q32

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PhysicsSingle correct+4 / -1Question 32 of 90

The electric current in a circular coil of 2 turns produces a magnetic induction $B_1$ at its centre. The coil is unwound and is rewound into a circular coil of 5 turns and the same current produces a magnetic induction $B_2$ at its centre. The ratio of $\dfrac{B_2}{B_1}$ is

\dfrac52

\dfrac{25}4

\dfrac54

\dfrac{25}2

Answer and worked solution

Official answer: B

Same wire. $n$ turns of radius $\frac{L}{2\pi n}$ : $B\propto\frac nr\propto n^2$ , so $\frac{25}4$ .

(B)

Topics:Biot-Savart law

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JEE Main 2022 · 25 Jul · Shift 2, Physics question 32