A circular coil of radius 'r' is placed on another circular coil whose radius is 'R' and the current flowing through it is changing and their centers coincide. ( R r). If both the coils are coplanar, then the mutual inductance between them is proportional to (a) r/R (b) R/r (c) R²/r (d) r²/R

Answer: (d). Field of big coil at centre: B = (μ₀ I)/(2R), uniform over the small coil ( R r) Φ = Bπ r² ⇒ M = (μ₀π r²)/(2R) So M ∝ r²/R; the answer is (d).

A circular coil of radius 'r' is placed on another circular coil… | MHT CET 2026 (16 Apr, Shift 2)

Q13MHT CET 2026 · 16 APR · SHIFT 2Easy

Mutual Inductance

A circular coil of radius 'r' is placed on another circular coil whose radius is 'R' and the current flowing through it is changing and their centers coincide. ( $R \gg r$ ). If both the coils are coplanar, then the mutual inductance between them is proportional to

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Answer: (d)

Field of big coil at centre: $B = \dfrac{\mu_0 I}{2R}$ , uniform over the small coil ( $R \gg r$ )
$\Phi = B\pi r^2 \Rightarrow M = \dfrac{\mu_0\pi r^2}{2R}$
So $M \propto \dfrac{r^2}{R}$ ; the answer is (d).

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Mutual Inductance question from MHT CET 2026 (16 Apr, Shift 2)

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