ElectricityUnit 8, Chapter 20

Pre-unit QuizDo the following sets of subatomic particles repel, attract, or do nothing?

proton

neutron neutron

neutron

protonproton

Do nothing

Do nothing

Repel

Page 1

electron neutron

electron

proton

electron

electron

Do nothing

Repel

Attract

Page 2

I. Electric Charges

1. Positive (+)2. Negative (-)

A. Types of electric charges

B. Properties of electric charges

1. Like charges repel

2. Opposites attract

+ +

+ -

(Force of repulsion)

(Force of attraction)

C. An object gains an electric charge by gaining or losing electrons

+

-

+

+

+

+

+ +

+

+

+

-

-

-

-

-

- -

-

-

Two neutral objectsPositive object Negative object

II. Static electricityA. Build up of electric charges

B. There are three ways to separate electric charge.

The first method of separating electric charge:

FRICTIONbefore after

Electrons transfer when two objects are rubbed against each other.

The second method of separating electric charge:

Inductionbefore after

A neutral object is charged oppositely when brought near a charged object.

The third method of separating electric charge:

Conductionbefore after

contact allowed

Electrons are transferred through contact.

Learn moreC. Van de Graaff generator

friction

static electric field

electroscope - detects electric fields

static electric discharge

ground wire

Robert Van de Graaff

D. Thunder storms

ice crystals+ updraft friction

inductioninduction

staticdischarge

staticdischarge

III. The flow of electricityA. Voltage (V)

1. Pushes the electrons through a wire (analogous to water pressure in a pipe)

2. Called potential difference

3. Measured in voltsBonus: Named after Count Alessandro Antonio Anastasio Volta

Count Volta invented the battery.

4. Sources of voltage

a. Batteries (chemical reaction)

b. Solar cells (light)

c. generator (mechanical/magnetic)

solar cell generator

B. Current (I)

1. Flow of electrons through a wire (analogous to the flow of water in a pipe)

2. Measured in amperes or amps

3. Detected by an ammeter

Bonus: Named after André Marie Ampère

Made discoveries in electromagnetism concerningelectric current

4. Two types of current

a. alternating current- AC

- current regularly changes direction

- can be transmitted over long distances

- produced by generators

b. direct current- DC

- produced by batteries and solar cells

- current travels in one direction only

C. Resistance (R)

1. Opposes the flow of electrons (analogous to a blockage in a water pipe)

2. Measured in ohms (W)

What would cause the

resistance in these

pictures?

3. Factors that affect resistance of a wire

a. length

b. thickness

c. temperature

d. type of material

- reducing temperature reduces resistance

D. Ohm’s Law

Voltage1. Current = Resistance

volts2. amps = ohms

V3. I = R

Georg Simon Ohm

IV. CircuitsA. A circuit is a complete

loop for electrons to flow aroundB. Circuit symbols

1. wire

2. switch

3. resistor

4. light

5. battery

6. ammeter

7. voltmeter

+-

V

A

C. Series circuit

1. Has only one path or loop

2. Total resistance equation

Rtotal = R1 + R2 + R3 + …

2 W

3 W

Rtot = 2 W + 2 W + 3 W = 7W

2 W

+-

D. Parallel circuit

1. Has more than one path or loop

2. Total resistance equation

THIS ONE IS TRICKY!

1 1 1 1

Rtotal R1 R2 R3 = + + + …

1 1 1

Rtotal 2 3 = +

1 3 2 5

Rtotal 6 6 6

= + =

6

5 Rtotal = = 1.2 W

2 W 3 W

+-

My Electric Bill

Electric companies multiply your electric use by A cost per KWH.

V. Electric PowerA. Power is measured in Watts

(W)

B. Power = voltage X current

P = VIWatts = volts x amps

James Watt invented the steam engine

VI. Electric EnergyA. Energy is measured

in kilowatt-hours

(kWh)

B. Energy = Power X time

E = PtkWh = kilowatts x

hours

PP&L’s definition