Untitled Lesson

Ch. 22 -

Electricity
I. Electric Charge

(p.592-597)

✦ Static Electricity
✦ Conductors
✦ Insulators
✦ Electroscope

A. Static Electricity

✦ Static Electricity

⬥ the net accumulation of electric

charges on an object

✦ Electric Field

⬥ force exerted by an e- on anything

that has an electric charge

⬥ opposite charges attract
⬥ like charges repel

A. Static Electricity

A. Static Electricity

✦ Static Discharge

⬥ the movement of

electrons to relieve a
separation in charge

B. Conductors

✦ Conductor

⬥ material that allows electrons to move

through it easily

⬥ e- are loosely held
⬥ ex: metals like copper and silver

C. Insulators

✦ Insulator

⬥ material that doesn’t allow electrons

to move through it easily

⬥ e- are tightly held
⬥ ex: plastic, wood, rubber, glass

D. Electroscope

✦ Electroscope

⬥ instrument that

detects the presence
of electrical charges

⬥ leaves separate

when they gain either
a + or - charge

Match

Match the following about charges.

• Like Charges

• Opposite Charges

• Positive Charge

• Neutral Charge

• Negative Charge

Attract

Repel

Protons

Neutron

Electron

• Attract

• Repel

• Protons

• Neutron

• Electron

Multiple Choice

What is the Unit of Electric Charge?

• Newtons

• Ohms

• Coulombs

• Volts

Ch. 22 -

Electricity
II. Electric Current

(p.598-599)

✦ Circuits
✦ Potential Difference
✦ Current
✦ Resistance
✦ Ohm’s Law

A. Circuit

✦ Circuit

⬥ closed path through

which electrons can flow

A. Potential Difference

✦ Potential Difference (voltage)

⬥ difference in electrical potential

between two places

⬥ large separation of charge creates

high voltage

⬥ the “push” that causes e- to move

from - to +

⬥ measured in volts (V)

A. Potential Difference

B. Current

✦ Current

⬥ flow of electrons through a conductor
⬥ depends on # of e- passing a point in

a given time

⬥ measured in amperes (A)

C. Resistance

✦ Resistance

⬥ opposition the flow of electrons
⬥ electrical energy is converted to

thermal energy & light

⬥ measured in ohms (Ω)

Copper - low resistance

Tungsten - high resistance

C. Resistance

✦ Resistance depends on…

⬥ the conductor

⬥ wire thickness

• less resistance

in thicker wires

⬥ wire length

• less resistance in shorter wires

⬥ temp - less resistance at low temps

E. Ohm’s Law

✦ Ohm’s Law

V = I × R

V: potential
difference (V)

I: current (A)

R: resistance (Ω)

• Voltage increases when current increases.
• Voltage decreases when resistance increases.

E. Ohm’s Law

✦ A lightbulb with a resistance of 160 Ω is

plugged into a 120-V outlet. What is the
current flowing through the bulb?

GIVEN:
R = 160 Ω
V = 120 V
I = ?

WORK:

I

V

R

Ch. 22 -

Electricity
III. Electrical Circuits

(p.608-613)

✦ Circuit components
✦ Series circuits
✦ Parallel circuits
✦ Household circuits

A. Circuit Components

A - battery

C - light bulb

B - switch

D - resistor

B. Series Circuits

✦ Series Circuit

⬥ current travels in a single path

• one break stops the flow of current

⬥ current is the same throughout circuit

• lights are equal brightness

⬥ each device receives a fraction of the

total voltage
• get dimmer as lights are added

C. Parallel Circuits

✦ Parallel Circuits

⬥ current travels in multiple paths

• one break doesn’t stop flow

⬥ current varies in different branches

• takes path of least resistance
• “bigger” light would be dimmer

⬥ each device receives the total voltage

• no change when lights are added

D. Household Circuits

✦ Combination of parallel circuits

⬥ too many devices can cause wires to

overheat

✦ Safety Features:

⬥ fuse - metal melts, breaking circuit
⬥ circuit breaker - bimetallic strip bends

when hot, breaking circuit

Ch. 22 -

Electricity

IV. Measuring Electricity

(p.614-618)

✦ Electrical Power
✦ Electrical Energy

A. Electrical Power

✦ Electrical Power

⬥ rate at which electrical energy is

converted to another form of energy

P = I × V

P: power (W)

I: current (A)

V: potential
difference (V)

A. Electrical Power

✦

A calculator has a 0.01-A current flowing through it.
It operates with a potential difference of 9 V. How
much power does it use?

GIVEN:
I = 0.01 A
V = 9 V
P = ?

WORK:

I

P

V

B. Electrical Energy

✦ Electrical Energy

⬥ energy use of an appliance depends

on power required and time used

E = P × t

E: energy (kWh)

P: power (kW)

t: time (h)

B. Electrical Energy

✦ A refrigerator is a major user of electrical power. If

it uses 700 W and runs 10 hours each day, how
much energy (in kWh) is used in one day?

GIVEN:
P = 700 W = 0.7 kW
t = 10 h
E = ?

WORK:

P

E

t

Ch. 22 -

Magnetism

I. Characteristics of Magnets

(p.624-627)

⬥Magnetism
⬥Magnetic poles
⬥Magnetic field
⬥Magnetic domain

A. Magnetism

� Magnetism

⬥ force of attraction or repulsion between

unlike or like poles

⬥ due to the arrangement of electrons

⬥ closely related to electricity

B. Magnetic Poles

� Magnetic Poles

⬥ like poles repel

⬥ unlike poles attract

⬥ a broken magnet creates new poles

C. Magnetic Field

� Magnetic Field

⬥ area around a magnet where magnetic

forces act

⬥ field lines show direction of field (N→S)

D. Magnetic Domain

� Magnetic Domain

⬥ groups of atoms with aligned magnetic

poles

⬥ in a magnetized object, domains are all

aligned

domain

Ch. 22 -

Magnetism

II. Uses of Magnetic Fields

(p.628-632)

⬥Electromagnet
⬥Speaker
⬥Motor

A. Electromagnet

� Electromagnet

⬥ strong, temporary magnet formed when

current is passed through a coil of wire
surrounding an iron core

⬥ acts like a bar magnet when current is on

B. Speaker

� Speaker

⬥ electrical energy → mechanical energy

⬥ wire coil moves back &

forth as its magnetic
field interacts with the
field of a fixed magnet

⬥ forced vibration causes

the cone to move ⇒
sound

C. Motor

� Motor

⬥ electrical energy → mechanical energy

⬥ electromagnet

rotates between
the poles of a fixed
magnet

⬥ commutator

reverses the poles
of the e’magnet

C. Motor

brushes & wires to battery

field
magnet

armature & commutator

assembled
motor

Ch. 22 -

Magnetism

III. Producing Electric Current

(p.633-639)

⬥Electromagnetic Induction
⬥Electric Generator
⬥DC & AC
⬥Transformer

A. Electromagnetic Induction

� Electromagnetic Induction

⬥ producing a current by moving a wire through a

magnetic field

⬥ some microphones

work just like
mini-speakers in
reverse

⬥ sound waves cause

coil to move → current
Dynamic

Microphone

Coi
l

B. Electric Generator

� Electric Generator

⬥ mechanical energy → electrical energy

⬥ armature is

rotated between
magnet poles

⬥ magnetic field

induces a
current in the
wire coil

MOTO
R

GENERAT
OR

B. Electric Generator

� Hydroelectric Dam

⬥ PE of lake water is

converted to KE

⬥ mechanical KE

turns the generator
shaft which creates
electrical energy

C. DC & AC

� Direct Current (DC)

⬥ current flows in one direction
⬥ dry cells

� Alternating Current (AC)

⬥ current reverses its direction

at regular intervals

⬥ electrical outlets

D. Transformer

� Transformer

⬥ increases or decreases AC voltage
⬥ primary coil AC produces a magnetic field that

induces AC in the secondary coil

⬥ voltage ratio = ratio of turns in each coil

D. Transformer

� Step-up Transformer

⬥ increases the voltage
⬥ more turns
⬥ power plants

� Step-down Transformer

⬥ decreases the voltage
⬥ fewer turns
⬥ household appliances

(hairdryers, etc.)