JEE Main · 2023 · 10 Apr 2023 · Shift 1 · Magnetic Properties of Matter

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The current required to be passed through a solenoid of 15 cm length and 60 turns in order to demagnetise a bar magnet of magnetic intensity

2.4 \times 1 0^{3} Am^{- 1}

is ____ A.

Answer: 6

Solution

Demagnetisation requires the solenoid's field intensity to match the magnet's intensity,

H = ni

, with turn density

n = \frac{N}{ℓ} = \frac{60}{0.15} = 400 m^{- 1}

. Then

i = \frac{H}{n} = \frac{2.4 \times 1 0 ^{3}}{400} = 6

. The required current is

6

JEE Main · 2023 · 10 Apr 2023 · Shift 1 · Integer answer

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