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A tightly wound solenoid has 2000 turns and a cross-sectional area of 1.5 × 10⁻⁴ m². It carries a current of 2.0 A and is hung at its center with its axis perpendicular to its length so that it can rotate in a horizontal plane. If it is placed in a uniform magnetic field of strength 5 × 10⁻² tesla, and the field makes an angle of 30° with the solenoid axis, what torque acts on the solenoid?

1. 3 × 10⁻² N-m
2. 3 × 10⁻³ N-m
3. 1.5 × 10⁻³ N-m
4. 1.5 × 10⁻² N-m

Correct answer: 1.5 × 10⁻² N-m

Solution

tau = N*I*A*B*sin(30) = 2000 * 2.0 * 1.5e-4 * 5e-2 * 0.5 = 1.5e-2 N-m.

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