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A dipole of moment p is placed in a uniform external field E. The torque on the dipole is:
Aτ = p · E
Bτ = p × E (magnitude pE sin θ; aligns p with E)
Cτ = pE always
Dτ = 0 always (no net force in uniform field)
Answer & Solution
Correct answer: B. τ = p × E (magnitude pE sin θ; aligns p with E)
**Torque τ = p × E** (cross product). |τ| = pE sin θ, where θ is angle between p and E. Tends to **align p with E**. **Net force = 0 in uniform E** (because forces on +q and −q are equal and opposite). In a **non-uniform field**, the dipole experiences both torque AND net force.
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