CHAPTER 16. ELECTROSTATICS

Electrostatics 16

Introduction and key

concepts

ESAEQ

Electrostatics is the study of electric charge which is at rest or static (not moving). In this

chapter we will look at some of the basic principles of electrostatics as well as the principle

of conservation of charge.

See introductory video: ( Video: VPfmg at http://www.everythingscience.co.za)

Two kinds of charge ESAER

All objects surrounding us (including people!) contain large amounts of electric charge.

There are two types of electric charge: positivecharge andnegativecharge. If the same

amounts of negative and positive charge are found in an object, there isno net chargeand

the object is electricallyneutral. If there is more of one type of charge than the other on

the object then the object is said to beelectrically charged. The picture below shows what

the distribution of charges might look like for a neutral, positively charged and negatively

charged object.

+ +

+

+

+

+-

- -

-

- -

+

+ +

+

+

+ +

- +

-

- -

-

- -+

++

+

+

+ -

-

- -

-

- -

-

There are:

6 positive charges and

6 negative charges

6 + (-6) = 0

There is zero net charge:

The object is neutral

8 positive charges and

6 negative charges

8 + (-6) = 2

The net charge is +2

The object is positively charged

6 positive charges and

9 negative charges

6 + (-9) = -3

The net charge is -3

The object is negatively charged

Positive charge is carried by the protons in material and negative charge by electrons. The

overall charge of an object is usually due to changes in the number of electrons. To make

an object:

Physics: Electricity and Magnetism 259