ELECTRICAL PRINCIPLES AND TECHNOLOGIESUnit 4

Topic 1

Questions to think about...

How do we turn coal in the ground or water behind a dam into electric energy that you can use in your home?

How are we able to control the energy so that the various appliances we use receive just the right amount?

What new technologies can we develop to help us use energy in less environmentally demanding ways?

Topic 1: Electric Charges

The electrical devices you use everyday, from light bulbs to computers, use the energy of moving charges to do useful work.

Producing Charges

Materials that attract and repel other materials are said to be charged, or carry an electric charge.

Van de Graaff How can you tell that thegirl touching the generatorhas also become electricallycharged?

Van de Graaff

Schematic view of a classical Van de Graaff-generator.1) hollow metal sphere2) upper electrode3) upper roller (metal)4) side of the belt with positive charges5) opposite side of the belt with negative charges6) lower roller (for example an acrylic glass)7) lower electrode (ground)8) spherical device with negative charges, used to discharge the main sphere9) spark produced by the difference of potentials

Charges produced by rubbing or touching remain stationary, so they are sometimes called static electricity.

Sometimes charges move, so unbalanced charges is a more accurate description.

The quantity of electric charge is expressed in coulombs (C)

There are 3 different interactions in terms of positive and negative charges in materials.

a. Neutral (uncharged): + + - + - -equal positive and - - + - + + negative charge

b. Positive charge: + + + + - + excess positive charge - - + + + +

c. Negative charge: - - + - - +excess negative charge - - - + - +

Benjamin Franklin (1706-1790)

1st to use the terms “positive” and “negative” to describe charges Unlike charges- two different

charges Like charges- charges of the same

type (both positive, or both negative)

What are positively charged particles called?

What are negatively charged particles called?

Laws of Charges:

1. Unlike charges attract2. Like charges repel3. Charged objects attract uncharged

(neutral) objects

According to modern theory, unbalanced charges on solid materials are due to the movement of electrons from one object to another.

Insulators vs. Conductors Insulators:

Materials that do not allow charges to move freely on or through them Examples:

Conductors: Materials that allow charges to move freely

Examples:

Fair conductors: Not prefect insulators, but are not good conductors

either. Examples:

Semiconductors: Materials with higher conductivity than insulators

but with lower conductivity than metals Ex: silicon and gallium

Superconductors: Materials that offer little, if any, resistance to the

flow charges Usually made of alloys and ceramics Take up less space and can carry higher charges that

ordinary conductors

Electric discharge: An accumulated charge where electrons either

enter an object to make up for a shortage, or an excess of electrons leave an object Small sparks

Why is this a safety hazard? (pg.270)

Grounding: A way of neutralizing conductive materials List some ways in which objects are neutralized.

(p. 270)

Ionization devices: Produce both positive and negative charges

REMEMBER: an ion is a charged particle!

Charged objects attract dust and contaminants

To Do:

Topic 1 Questions: