Week 3:Problem 4.5, Problem 4.6, Problem 4.9, 4..1.4 Polarization

 

Introduction:

In the previous two sections, we have considered the effect of an external electric field on an individual atom or molecule. We are now in a position to answer (qualitatively) the original question:What happens to apiece of dielectric material when it is placed in an electric field? If the substance consists of neutral atoms (or nonpolar molecules), the field will induce in each a tiny dipole moment, pointing in the same direction as the field. If the material is made up of polar molecules, each permanent dipole will experience a torque, tending to line it up along the field direction. (Random thermal motions compete with this process, so the alignment is never complete, especially at higher temperatures, and disappears almost at once when the field is removed.)

Notice that these two mechanisms produce the same basic result: a lot of little dipoles pointing along the direction of the field—the material becomespolarized. A convenient measure of this effect is dipole moment per unit volume, which is called the polarization.

Learning Outcomes:

In this week

  • we'll solve the problem related to rotational effect and linear force acting on dipole under the action of external field.
  • We'll learn  net effect of individual dipoles to dielectric material, which is call the polarization.

Lecture Plan:

Lecture 1: 

  • Problem 4.5:Torque on electric dipole due to external electric field of another electric dipole
  • Problem 4.6:Torque on electric dipole due to external electric field of grounded plane
  • Assignment: Calculate the potential energy of dipole in external field

Lecture 2:

Problem: 4.9:

  • Force on electric dipole due to external field of charge q.
  • Force on charge q due to external field of electric dipole.

 

Lecture 3:

  • Problem 4.8 : Interaction energy of dipole
  • 4..1.4 Polarization

Download Files

problem-4.pdf (0.95 MB )

problem-4.pdf (0.85 MB )