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A moving coil galvanometer has a coil with 175 turns and area 1 cm². It uses a torsion band of torsion constant 10⁻⁶ N-m/rad. The coil is placed in a magnetic field B parallel to its plane. The coil deflects by 10° for a current of 1 mA. The value of B (in Tesla) is approximately:

1. 10⁻³
2. 10⁻¹
3. 10⁻⁴
4. 10⁻²

Correct answer: 10⁻²

Solution

The correct option is 10⁻² because the deflection angle of the coil is directly related to the magnetic field strength, the current, and the physical properties of the coil. Using the formula for torque in a galvanometer, we can derive that the magnetic field strength must be approximately 0.01 T to produce a 10° deflection at 1 mA.

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