Two charges each of magnitude 0.01 C separated by 0.4 mm form a dipole. It is placed in a uniform electric field of 10 dyne C⁻¹ at 30°. The torque magnitude is:
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Question

Two charges each of magnitude 0.01 C separated by 0.4 mm form a dipole. It is placed in a uniform electric field of 10 dyne C⁻¹ at 30°. The torque magnitude is:

G1 Physics · Accepted Answer

Dipole moment: p = qd = 0.01×0.4×10⁻³ = 4×10⁻⁶ C m Field: 10 dyne C⁻¹ = 10×10⁻⁵ N C⁻¹ = 10⁻⁴ N C⁻¹ Torque: τ = pE sin30° = (4×10⁻⁶)(10⁻⁴)(1/2) = 2×10⁻¹⁰ N m Hence option B follows.