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The torque on an electric dipole of dipole moment P placed in a uniform electric field of intensity 5×10⁴ N C⁻¹, making an angle of 30° with the field, is 1×10⁻⁴ N m. Then P=

Asked in GSEB Board March 2020 (old course) · Torque, energy and work done

• (1) 2×10⁻⁹ C m
• (2) 4×10⁻⁶ C m
• (3) 4×10⁻⁹ C m
• (4) 2×10⁻⁶ C m

Step-by-step solution

Why the other options are wrong

• (1) Leaves out sin 30°: (1×10⁻⁴)/(5×10⁴)=2×10⁻⁹. The torque is PE sin θ, and sin 30°=1/2 doubles the answer.
• (2) Right digits, three powers of ten too large; no single slip gives it. Sanity check: (10⁻⁴)/(2.5×10⁴)=4×10⁻⁹.
• (4) Combines the missing sin 30° of 2×10⁻⁹ with a power-of-ten error; no single slip gives it.

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