JEE Main · 2026 · 23 Jan 2026 · Shift 2 · Electromagnetic Induction

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A circular loop of radius 7 cm is placed in uniform magnetic field of 0.2 T directed perpendicular to plane of loop. The loop is converted into a square loop in 0.5 s. The EMF induced in the loop is

____

mV.

(A)6.6
(B)13.2
(C)8.25
(D)1.32✓ Correct

Answer: (D)

Solution

The circular loop of radius

r = 7 cm

has circumference

2 π r = 14 π cm

, so the square made from the same wire has side

\frac{14 π}{4} = \frac{7 π}{2} cm

. The areas are

A_{1} = π r^{2} = 49 π cm^{2}

and

A_{2} = (\frac{7 π}{2})^{2} = \frac{49 π ^{2}}{4} cm^{2}

. The magnitude of the area change is

A_{1} - A_{2} = 49 π - \frac{49 π ^{2}}{4} = 49 π (1 - \frac{π}{4}) \approx 33.1 cm^{2} = 33.1 \times 1 0^{- 4} m^{2}

. The flux change is

Δ ϕ = B Δ A = 0.2 \times 33.1 \times 1 0^{- 4} = 6.6 \times 1 0^{- 4} Wb

, and the induced emf is

ε = \frac{Δ ϕ}{Δ t} = \frac{6.6 \times 1 0 ^{- 4}}{0.5} = 1.32 \times 1 0^{- 3} V = 1.32 mV

JEE Main · 2026 · 23 Jan 2026 · Shift 2 · Single correct option

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JEE Main · 2026 · 23 Jan 2026 · Shift 2 · Electromagnetic Induction

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