A small rigid dipole is made of charges and held apart

PHYSICS · Multi-part · Fermi University Physics · Electricity, Magnetism & Electromagnetism · Electrostatic fields and potential · Electrostatic fields and potential

Electricity, Magnetism and Electromagnetism, Ch Electric charge, Coulomb's law and the electric field

Problem

A small rigid dipole is made of charges +2.0 nC+2.0\,\mathrm{nC} and −2.0 nC-2.0\,\mathrm{nC} held 4.0 mm4.0\,\mathrm{mm} apart. It sits in a uniform field E\mathbf{E} of size 5.0×104 V m−15.0\times10^{4}\,\mathrm{V\,m^{-1}} along +x+x, with its dipole moment p\mathbf{p} in the xyxy-plane at 60∘60^\circ anticlockwise from +x+x, seen from +z+z. ((a)) What is the net force on the dipole? ((b)) Find the size of the torque on it, and say which way it turns the dipole, seen from +z+z. ((c)) How much work must an external agent do to turn the dipole slowly from this position until p\mathbf{p} points along −x-x?

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