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IGCSE Electricity – Simple Circuits

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Current

• state that current is related to the flow of charge• use and describe the use of an ammeter• show understanding that a current is a rate of flow of charge and recall and

use the equation l = Q/t• distinguish between the direction of flow of electrons and conventional

current

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Circuit symbols

Instead of drawing intricate diagrams of electrical components we use circuit symbols to simplify how circuits are set up.

You will need to learn these, how to draw them, and how to identify them.

Filament lamp

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Use a textbook or other resource to fill in the table below:

Component Circuit symbol

Fuse

Switch

Resistor

Motor M

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Component Circuit symbol

Cell

Voltmeter

Battery

Ammeter A

V

Use a textbook or other resource to fill in the table below:

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Breaks in circuits

Set up the circuit shown….

…does the bulb light?

Why does the bulb not light?

There is a break in the circuit.

For electricity to flow in a circuit it must be able to flow from one terminal of the cell or battery to the other terminal.

NO

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Letting electricity pass

Do all materials let electricity pass?

Which materials will and which materials will not?

Set up the circuit shown and place different materials in the gap in the circuit. Record which materials let electricity through (the bulb lights if electricity flows).

What do we call a material that lets electricity flow through it? CONDUCTOR

What do we call a material that does not let electricity flow through it?

INSULATOR

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Which of these bulbs will light? Build the circuits!

A.

B.

C.x

x

Electricity will always take the easiest path.

It is easier to flow through a wire than through the bulb.

So in circuits B and C the electricity does not pass through the bulb.

The cell or battery still loses energy because , electricity is still flowing.

This type of circuit is known as a SHORT CIRCUIT.

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Electron flow

Electricity in wires is a flow of electrons along the wire.

What do we call this flow of electrons? Electrical current

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When we talk about current flowing we say that current flows out of the positive terminal of the cell and back into the negative terminal.

Current Flow

Conventional CurrentWhat do we call this flow?

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However, the electrons flow from the negative side of the battery to the positive side. These are the particles which are actually moving through the conductor.

Electron Flow

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When electrons were discovered, physicists worked out what was really happening. Negatively charged electrons are repelled out of the negative terminal of the cell. They then travel round the circuit and are attracted back to the positive terminal.

Conventional current and Electron flow

Conventional current electrons

Conventional current

What charge do electrons have?

Negative

What do two negative charges do if placed near to each other? They will repel each other.

What will a positive and a negative charge do to each other? They will attract each other.

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In an electric c____, current is the flow of c_______. The bigger the current, the m___

charge is flowing around the circuit. The w___ carry the electrons from one terminal

around the circuit to the other t______.

Current

lamps

ircuitharge ore

ireserminal

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Current

• Current=Charge/time• I=Q/t• Q is measured in Coulombs (C)• t is measured in seconds (s)• I is measured in Amperes (A)

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Set up the two circuits shown:

In which circuit are the bulbs the brightest?

BRIGHTER

DIMMER

A.

B.

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Measuring current• To find the current through a component

connect an ammeter next to the component (in series)

• Make sure the + side of the ammeter is connected nearest to the + side of the power supply

• All of the current flowing through the component must pass through the ammeter

• Now measure the current in each bulb in your circuits

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Set up the two circuits shown:

Which bulbs have the largest current?

MORE CURRENT

LESS CURRENT

A.

B.

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Charge, current and time

We can express a relationship between charge, current and time mathematically using the equation:

Charge = Current x time

Q=It

Charge measured in Coulombs (C)

Current measured in Amps (A)

Time measured in seconds (s)

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Formula triangles

Q

I t

x

Formula triangles help you to rearrange formula, the triangle for Q=It is shown below:

Whatever quantity you are trying to find cover it up and it will leave you with the calculation required.

So if you were trying to find current, I…..

…you would cover I up…

…and you are left with the sum…

I = Q

t

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A current of 6A flows for 3 minutes. How much charge flows?

Q = It

= 6A x (3x60)s

= 1080 C

In an examination you will not gain a mark for just writing Q=It.

You must write out the whole formula:

Charge = Current x time

Always convert time to

seconds!!!

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To do

• P176-177• Answer questions 1-4

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Progress check

• state that current is related to the flow of charge• use and describe the use of an ammeter• state that current is a rate of flow of charge• use the equation l = Q/t• distinguish between the direction of flow of electrons

and conventional current