Electricity and Magnetism Unit E1 Electrostatics

Overview: This unit treats situations in which all charges are held in fixed positions (by some force other than electromagnetic???). There are then no magnetic forces and the electric forces will not change with time, greatly simplifying the calculations.

E. M. Purcell, Electricity and Magnetism, Berkeley Physics Course, Vol. 2, 2nd Ed. , Chapt. 1 - Electrostatics: Charges and Fields, Sec. 1.1-1.5, 1.7-1.13; Chapt. 2 - The Electric Potential, Sec. 2.1-2.6

COMMENT:

This unit will begin the study of electricity and magnetism which will introduce more sophisticated mathematics as one progresses. In this unit we introduce vectors and use some vector algebra and simple vector calculus. (If you have difficulty with vectors, refer to Kleppner and Kolenkow, Chapt.1, or the corresponding early chapter is almost any elementary physics book.) We will return to mathematical discussion in the latter part of Chapt. 2, after Sec. 2.6, when we take up magnetism in Unit E3. It is assumed that you are already acquainted with Coulomb's Law and the concept ot the electric field and some of its properties. We will review much of what you know, but in terms of vectors and calculus. Many people have trouble with the concept of the electric field. Make sure that you understand it before leaving this unit.

After completing this unit you should understand:

• Charges and Coulomb's Law.
• Electric fields and lines of force.
• Electric fields in and near conductors.
• Gauss' law.
• When Gauss' law is useful: symmetric situations.
• Electric potential and potential energy.

Question:

Draw the lines of force around two positive charges. (You may find Fig. 1.11 in Purcell useful.)

Problems:

Purcell 1.4, 1.15, 1.16, 2.7