The electric dipole is situated in an electric field as shown in figure. The dipole and electric field are both in the plane of paper. The dipole is rotated about an axis perpendicular to the paper at point A in anticlockwise direction. If the angle of rotation is measured with respect to the direction of the electric field, then the torque require to hold the dipole at rest for different values of the angle of rotation θ will be as represented in fig. (b).
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The torque τ on an electric dipole in a uniform electric field is given by τ = pE sinθ, where p is the dipole moment, E is the electric field strength, and θ is the angle between the dipole moment vector and the electric field vector.
This is a sine function: . As the dipole is rotated anticlockwise, θ increases from 0 to 360 degrees. The torque is zero at θ = 0° and θ = 180°, and reaches maximum magnitude at θ = 90° and θ = 270°. The graph of torque vs. θ is a sine wave, which is symmetric about the origin and periodic.
Final Answer: b