A simple dipole consists of two charges with the same magnitude, q, but opposite sign separated by a distance d. The EDM (electric dipole moment) of the configuration is represented by p which has a magnitude p = qd and a direction pointing from the negative charge towards the positive charge. If the dipole is located in a region with an electric field, E, then it experiences a torque τ = p × E. In this problem we will explore the rotational potential energy of an electric dipole in an electric field. Enter an expression, in simplified form, for the amount of work, dW, done by the electric field on the dipole when it undergoes a rotation by dθ.

a. dW = ∫pEsinθdθ  b. W = p.E

Explanation:

a. We know torque τ = p × E = pEsinθ where θ is the angle between p and E

Let the torque τ rotate the dipole by an amount dθ. So, the workdone dW = ∫τdθ = ∫pEsinθdθ

b. So, the total work done is gotten by integrating from 90 to θ. So,

W = ∫₉₀⁰dW

= ∫₉₀⁰pEsinθdθ

= pE∫₉₀⁰sinθdθ

= pE(cosθ - cos90)

=pEcosθ

= p.E

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia