A dipole of moment 3 10 -8 C m is rotated in a uniform electric field of 2 10 5 N/C from 60 to 120 . The increase in its potential energy is:

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A dipole of moment 3 × 10-8 C m is rotated in a uniform electric field of 2 × 105 N/C from 60° to 120°. The increase in its potential energy is:

Answer: 6 10 -3 J.

A 3 × 10-3 J
B 6 × 10-3 J
C 9 × 10-3 J
D 1.2 × 10-2 J

Correct answer: B. 6 × 10-3 J

Explanation: U = -pE cosθ, so ΔU = -pE(cos120° - cos60°) = -pE(-0.5 - 0.5) = pE = 3 × 10-8 × 2 × 105 = 6 × 10-3 J.

Field lines always point from positive to negative charge, are denser where the field is stronger, and never cross; an isolated positive charge has lines radiating symmetrically outward, while a dipole's lines curve from the positive to the negative charge.

Concept context

Coulomb's law, electric field, potential, capacitors, Gauss's law.

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A dipole of moment 3 &times; 10<sup>-8</sup> C m is rotated in a uniform electric field of 2 &times; 10<sup>5</sup> N/C from 60&deg; to 120&deg;. The increase in its potential energy is:

Concept context

More Electric Charges and Fields questions

A dipole of moment 3 × 10<sup>-8</sup> C m is rotated in a uniform electric field of 2 × 10<sup>5</sup> N/C from 60° to 120°. The increase in its potential energy is: