Chapter 32

Electrostatics

Electrostatics involves electric charges, the forces between them, and their behavior in

materials.

Electrical Forces and Charges

• Just like gravity there is a force between electric charges. These forces are billions of times stronger than gravitational forces.

• There are two types of charges.• We call them positive(+) and

negative(-).

Defining Electrostatics

• Electro: Electron

• Static: Stationary

• Electrostatics

is the study of

stationary electrons and protons.

Like charges Repel Unlike charges attract.

2 + charges + and - charge 2 - charges

Repel Attract Repel

Charge has UNITS!!!

An electron has a charge of -1.– The electron has a negative charge.

A Proton has a charge of +1.– The proton has a positive charge.

•We represent a charge with the letter q.

•We measure charge incoulombs (c).

Charles-Augustin de Coulomb (14 June 1736 – 23 August 1806)

Insulator Vs. Conductor

Insulator– Not many electrons that can move freely

throughout the material– Atoms in material do not let their electrons go.

Conductor– Many electrons float freely through the materials.– Atoms in material let some of their electrons float

freely.

Semiconductors

• Materials that can act like an insulator or a conductor.

• Passing enough electricity through a semiconductor will make it turn from an insulator to a conductor.

• Semiconductors are the materials used to make computer chips.

There is a force between charges.

Recall: Force of gravity between two objects

Now: Force between charges.

€

Fgravity =Gm1m2

d2

€

Felectric charge = kq1q2

d2

Gravity Vs. Electric Charge

Magnitude: Size

Inverse: As distance gets bigger, Force gets smaller

Attractive: pull together

Repulsive: Push apart

How We Charge Objects.• Charging by friction or contact.

– Rub your shoes across a rug (friction)– Then shock your friend. (contact)

• Charging by Induction– Bring a charged object next to another

charged object. No physical contact.

Grounding

• Electrons want to be next to the opposite charge.

• When we ground something charged we give the electrons a path to be where they want to be.