1 of 10© boardworks ltd 2015 electrical circuits

1 of 10 © Boardworks Ltd 2015

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


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 connected

two 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


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 = Qt

current = chargetime


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 = WQ

voltage = work done

charge


If several cells are connected in series, the total voltage across the battery can be found by adding the voltages of the cells. 3 V

4.5 V

Using more cells in a battery increases the voltage.

So, if 2 cells with a voltage of 1.5 V are connected together, the voltage across the battery is 3 V.

When three cells of 1.5 V are connected, what is the voltage across the battery?

V

1.5 V

V

V

How can battery voltage be increased?


Current and voltage – true or false?

1 of 10© boardworks ltd 2015 electrical circuits

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