S.MORRIS 2006

Currents CIRCUITSCurrents CIRCUITS

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2 types of electric currents2 types of electric currentsAC = Alternating current

• Electrons in the circuit move in 1 direction for some time and then switch directions and go the opposite way • Ex: household outlets and appliances

•DC = Direct current• Charges always flow in the same

direction• From negative to positive• Ex: batteries

The CELL – the power The CELL – the power sourcesource

Cells are a type of voltage source that converts

chemical energy into electrical energy when a

circuit is connected.

When two or more cells are connected together we call this a Battery.

What is an electric circuit?Any pathway through which electrons can flow/travel

+ -

The bare essentials for a circuit:• battery/power source• Load (lightbulb/lamp)• Wires

One more piece…Most circuits also have a switch that is used to turn the circuit on and off

when the switch is open, it creates a gap so that electrons cannot flow

when the switch is closed, the circuit is complete and electrons can move through it

types of circuittypes of circuitThere 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.A break anywhere in the loop will result in an open circuit and no more moving electrons

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.If there is a break in one path, it might not effect the other path

The components are connected side by side.

circuit diagramcircuit diagram

cell switch

lamp

wires

Scientists usually draw electric circuits using symbols;

measuring currentElectric current is measured in amps (A) using an

ammeter which is 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.

2A 2A

2A

• current is shared between the components

2A2A

1A

1A

Discuss with your neighbor what the missing ammeter readings would be

?

?

4A

4A

4A

3A?

?

1A

?

3A

1A

1A

measuring voltageThe ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter which is drawn across (on top of) circuit components

V

V

measuring voltage

V

V

V

This is how we draw a voltmeter in a circuit.

SERIES CIRCUITPARALLEL CIRCUIT

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

Let’s recap:Series Circuit

Parallel Circuit

Current

Voltage

measuring current & voltage

copy the following circuits on the next two slides.

complete the missing current and voltage readings.

remember the rules for current and voltage in series and parallel circuits.

measuring current & voltage

V V

6V4A

A

A

a)a)

measuring current & voltage

V

V

6V4A A

A

A

b)b)

answers

3V 3V

6V

4A 4A6V

6V

6V4A 4A

2A

2A

4A

a)a) b)b)

measuring resistance in seriesIn series: to find total resistance of a series circuit, add

the individual resistances of the objects in series

The total resistance of this circuit would be 5 Ω

6V

3 Ω 2 Ω

What happens to voltage as you move past each light?

-It drops – we can calculate the “voltage drop” of each light using Ohm’s law

6V

3 Ω 2 Ω

measuring resistance in parallelIn parallel, use the following formula to find the total

resistance:

RT = R1 x R2 =

R1 + R2

Total resistance in parallel will always be less than the smallest resistor

3 Ω

2 Ω

6V 6V