An electric dipole with dipole moment 4×10⁻⁹ C m is aligned at 30° with the direction of a uniform electric field of magnitude 5×10⁴ N C⁻¹. The magnitude of the torque on the dipole is

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(4) 10⁻⁴ N m. Given: p=4×10⁻⁹ C m, E=5×10⁴ N C⁻¹, θ=30°. Idea: the forces on the two charges are equal and opposite, so they form a couple of moment τ=pE sin θ. τ=4×10⁻⁹×5×10⁴×sin 30°=2×10⁻⁴×0.5 τ=10⁻⁴ N m

An electric dipole with dipole moment 4×10⁻⁹ C m is aligned at 30° with the direction of a uniform electric field of magnitude 5×10⁴ N C⁻¹. The magnitude of the torque on the dipole is

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