Electrical Circuits - St Edmund's Girls'...

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Electrical Circuits


source of energy

What is an electric circuit?

An electric circuit is

a path for electric

charge to flow along.

Like all electrical

devices, this

portable MP3 player

contains electric

circuits to enable it

to play music.

What is needed for an electric circuit to work?

a complete loop

a component no short circuits


A model can help

us to understand

how current works

in an electric circuit.

What do the pizza shop and the

house of party-goers represent?

In this model, the

moped riders

represent the flow

of charge and the

pizzas represent

the electrical

energy carried

around the circuit.

How can we model electric circuits?


What are conductors and insulators?

Conductors are materials

that allow the flow of

electric charge. Metals are

good conductors.

Insulators are materials that

do not allow the flow of

electric charge. Plastics are

good insulators.

In some materials, electric charges are free to flow, but in

others, they are not. This means the current cannot flow.


The delocalized electrons are

free to flow through the metal

and so carry a current.

Insulating materials do not

contain free electrons and

so current is unable to flow.

Ionic solutions are also able

to conduct electricity

because they have mobile

charge-carrying particles.

It is the delocalized electrons involved in metallic bonding

that allow metals to conduct electricity.

delocalized electrons

How do metals conduct electricity?


Does it conduct?


Why do cables have plastic coatings?

To prevent electric shocks,

the metal wires are coated

with a thick layer of plastic.

Electricity and electric wires can be very dangerous.

Insulators can be used to make wires safer.

Metals, usually copper, are

used to make electrical wires

because they conduct current.

Plastic is an insulator and

does not conduct current.

How does this increase safety?

It is also important to insulate wires because if any part of

the circuit is earthed, the charge will not flow.


Conductors and insulators


Which competitor is finding it easier to build a circuit?

Using circuit diagrams


Electronic circuits are

usually very complex.

It is important to have a

clear way of showing how

different components are

connected together.

A standard set of symbols

is used to represent

different devices and to

draw schematic diagrams

of circuits, which show

how the components

are connected.

Why use circuit diagrams?


Wires or leads are used to carry

the current around a circuit

between the components.

circuit symbol for a wire

They are usually made from thin

copper wires twisted together and

covered with a plastic sleeve.

Circuit diagrams can be complex and it is important to be

able to distinguish between wires that are joined together

and those that cross without being joined.

two wires that

are connectedtwo wires that cross

(i.e. not connected)

How are wires shown in circuit diagrams?


What is the source of energy in a circuit?

When mains electricity is

unsuitable, cells or batteries

can be used as the source of

electrical energy.

Circuit symbol

for a cell

Mains electricity is often used

to power electric circuits.

This remote control uses batteries.

Circuit symbol

for a battery V


Circuit components


Circuit symbols


Current will always pass along the path of least resistance.

The resistance of the wires in a circuit is low compared to

the resistance of components, such as bulbs.

The current can only

pass through the bulb.These circuits both

contain a short circuit, so

the bulb will not be lit up.

If current can flow along a path without passing through the

components this part of the circuit is called a short circuit.

What is a short circuit?


Which circuit diagram?


Current is a measure of the rate of flow of electric charge

in a circuit. Electric charge is measured in coulombs.

A

An ammeter must be

connected in series

as it measures the

current flowing

through it.

A current of 1 A is 1 coulomb of

charge flowing every second.

So, a current of 5 A is 5 coulombs

of charge flowing every second.

What is current?

Current is measured in amperes

(A) using an ammeter. It is

calculated using the equation:

or I = Q

tcurrent = charge

time


Potential difference is the work done (or energy transferred)

between two points in a circuit, per coulomb of charge.

Potential difference is also called voltage.

Voltage is measured in volts (V) using a voltmeter.

The voltage of a battery is the “push”

it gives the charges in the circuit.

A 1 V cell gives 1 joule (J) of

energy to each coulomb of charge.

So, a 12 V battery gives 12 J of

energy to each coulomb of charge.

A voltmeter must be

connected in parallel

as it measures the

potential difference

across the component.

V

What is potential difference?

or V = W

Qvoltage =

work done

charge


Water model of a circuit


A cell is a source of electricity.

People often refer to cells as batteries, however they are not

the same and it is important to use the terms correctly!

A chemical reaction takes

place inside the cell,

which produces a

potential difference

(voltage) across the cell.

Are they cells or batteries?

A battery consists of two or more cells that are joined together.

The potential difference across a battery is the sum of the

potential differences across the cells.


If several cells are connected in

series, the total voltage across

the battery can be found by

adding the voltages of the cells. 3V

4.5V

Using more cells in a battery

increases the voltage.

So, if 2 cells with a voltage

of 1.5V are connected

together, the voltage

across the battery is 3V.

When three cells of 1.5V are

connected, what is the

voltage across the battery?

V

1.5V

V

V

How can battery voltage be increased?


Current and voltage – true or false?


This way of representing the

direction of current is called

conventional current.

It is now know that charge is

carried by electrons, flowing

from the negative terminal

to the positive terminal.

This is called electron flow.

Before the discovery of the electron, scientists assumed that

current was due to positively-charged particles moving from

the positive terminal around a circuit to the negative terminal.

Today, both conventional current and electron flow can be

used to represent the direction of current.

What is conventional current?


Representing current direction


Glossary


Anagrams


Multiple-choice quiz

Electrical Circuits - St Edmund's Girls'...

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