Electricity

Part I – Circuits

People

Benjamin Franklin

Thomas Edison

Have you heard of these people?

Why are they important?

Benjamin Franklin

Proved that lightning was electricity by

flying a kite in a lightning storm

Helped people understand the principles

of electricity

• Thomas Edison

– Invented the electrical light bulb

What is electricity?

Electricity is a form of energy

It is caused by a flow of tiny particles called

electrons through a material

Electricity

Electricity is a flow of electric charges along a wire.

Electricity

Electricity is a flow of electric charges along a wire.

Electricity

Electricity is a flow of electric charges along a wire.

Electricity

Electricity is a flow of electric charges along a wire.

Electricity

Electricity is a flow of electric charges along a wire.

Electricity

Electricity is a flow of electric charges along a wire.

Electricity

Electricity is a flow of electric charges along a wire.

This flow of electric charge is called a current.

Current is measured in the units of Amps (A).

What is an Electrical

Circuit?

A circuit is an electrical device that provides a

path for electricity to flow

Complete or Incomplete?

A complete circuit is where all the components of

a circuit are joined up and there are no gaps

The pathway for electricity is complete

Complete or Incomplete?

An incomplete circuit is where the pathway for

electricity is broken

The electricity cannot flow

Circuit Diagrams

cell switchlamp wires

Component Symbols – a

cell The cell stores chemical

energy and transfers it to

electrical energy when a

circuit is connected.

The long line is the positive end

The short line is the negative end

Battery

When two or more cells

are connected together

we call this a Battery.

The cells chemical energy is used up pushing a current round a circuit.

It is important that each

cell faces the right way

Switch

A switch can be open (as

shown) or closed

When the switch is open, the circuit is incomplete – no

electricity can flow

What happens when the switch is

closed?

Bulb / Lamp

The lamp lights up when

electricity flows through it

What would happen to a

lamp if there was an open

switch in the circuit?

Wires

The wires which carry electricity consist of two parts:

• The metal wires (conductor).

• The plastic coating around the metal wires (insulator).

• Prevents people from being electrocuted.

wires

Voltmeter

The voltmeter measures

the voltage of the circuit

We will discuss this in

another lesson

Ammeter

The ammeter measures

the current in the circuit

We will discuss this in

another lesson

Resistor

A resistor can change the amount of current in a circuit

In a variable resistor, the resistance can be changed.

Resistance

Variable resistors

Look at Figure 17.6 on page 207.

Path of current flow

Terminal A metal bar sliding contact coils of wire Terminal B

Variable resistors

Look at Figure 17.6 on page 207.

The sliding contact can be adjusted so that the current passes

through only a few coils of wire or many coils of wire.

If the sliding contact is near Terminal A : current passes through

many coils of wire = high resistance

If the sliding contact is near Terminal B: current passes through a

few coils of wire = low resistance

Variable resistors

Turn the dial here for

low resistance higher resistance

Fuse

A fuse is a safety device

When the current is too

high, the fuse breaks

Example

The wire inside a 3A fuse will melt when the current is greater than 3A.

Motor

A motor can be fitted

into a circuit

What do you think

happens to a motor in

a complete circuit?

Circuit Symbols

Voltmeter

Ammeter

Variable Resistor

Switch

Bulb

Motor

Cell

Battery

types of circuit

There are two types of electrical circuits;

SERIES CIRCUITS PARALLEL CIRCUITS

The components are connected end-to-end, one after the other.

They make a simple loop for the current to flow round.

SERIES CIRCUITS

If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.

PARALLEL CIRCUITS

The current has a choice of routes (paths).

The components are connected side by side.

If one bulb ‘blows’ there would still be a complete circuit to the other bulb so it stays lit.

measuring current

Electric current is measured in amps (A) using

an ammeter connected in series in the circuit.

A

measuring current

A A

This is how we draw an ammeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUIT

measuring currentSERIES CIRCUIT

PARALLEL CIRCUIT

• current is the same

at all points in the

circuit.

6A 6A

6A

• current is shared between the components

4A4A

3A

1A

copy the following circuits and fill in the missing ammeter readings.

?

?

4A

4A

4A

3A?

?

1A

?

3A

1A

1A

measuring voltage

The ‘electrical push’ which the cell gives to the current

is called the voltage. It is measured in volts (V) on a

voltmeter

V

Different cells produce different voltages.

The bigger the voltage supplied by the cell, the bigger

the current (the cell gives a bigger push to the

electrons).

measuring voltage

measuring voltage

Unlike an ammeter a voltmeter is connected across

the components (in parallel)

Scientist usually use the term Potential Difference

(pd) when they talk about voltage.

Final GPE

Initial GPE

PotentialDifference

pd

measuring voltage

V

This is how we draw a voltmeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUIT

V

V

measuring voltage

VV

V

series circuit

1.5V

• voltage is shared between the components

1.5V

3V

• voltage is the same in all parts of the circuit.

3V

parallel circuit

3V

3V

measuring current & voltage

V V

6V4A

A

A

a)

measuring current & voltage

V

V

6V4A A

A

A

b)

answers

3V 3V

6V

4A 4A6V

6V

6V4A 4A

2A

2A

4A

a) b)