JEE Main · 2021 · 26 Aug 2021 · Shift 2 · Magnetic Effects of Current

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A coil in the shape of an equilateral triangle of side 10 cm lies in a vertical plane between the pole pieces of permanent magnet producing a horizontal magnetic field 20 mT. The torque acting on the coil when a current of 0.2 A is passed through it and its plane becomes parallel to the magnetic field will be

x \times 1 0^{- 5} Nm

. The value of

x

is _____.

Answer: 3

Solution

With the plane of the coil parallel to the field, its normal is perpendicular to the field and the torque takes its largest value,

τ = N I A B

.
For an equilateral triangle of side

a = 0.1

A = \frac{3}{4} a^{2} = \frac{3}{4} (0.1)^{2} = 2.5 3 \times 1 0^{- 3} m^{2}

With

N = 1

I = 0.2

A and

B = 20 \times 1 0^{- 3}

τ = (0.2) (2.5 3 \times 1 0^{- 3}) (20 \times 1 0^{- 3}) = 3 \times 1 0^{- 5} N m

Comparing with

x \times 1 0^{- 5}

N m gives

x = 3

JEE Main · 2021 · 26 Aug 2021 · Shift 2 · Integer answer

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JEE Main · 2021 · 26 Aug 2021 · Shift 2 · Magnetic Effects of Current

Solution

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