Question

A dipole moment is placed in a uniform electric field oriented along an unknown direction. The maximum torque applied to the dipole is equal to 0.1 N.m. When the dipole reaches equilibrium its potential energy is equal to -0.2 J. What was the initial angle between the direction of the dipole moment and the direction of the electric field?

Answer 1

θ = 180

Step-by-step explanation:

When an electric dipole is placed in an electric field, there is a torque due to the electric force

τ = p x E

by rotating the dipole there is a change in potential energy

ΔU = ∫ τ dθ

ΔU = p E (cos θ₂ - cos θ₁)

when the dipole starts from an angle to the equilibrium position for θ = 0

ΔU = pE (cos θ - cos 0)

cos θ = 1 + DU / pE)

let's apply this expression to our case, the change in potential energy is ΔU = -0.2J

let's calculate

cos θ = 1 -0.2 / 0.1

cos θ = -1

θ = 180