# 3.6 Component 6 – Physics: Electricity, magnetism and waves

Electricity is used in domestic and industrial situations to supply energy. Electric current is a flow of electrical charge and measured in amps. Direct current (d.c.) is supplied by cells and alternating current (a.c.) is supplied by the mains, but in both cases the size of the current depends on the resistance in the circuit. When a current flows through a coil of wire an electromagnet is formed, which like permanent magnets, can exert a force over a distance.

Electric currents can also be used to produce electromagnetic waves, which have many uses including the transmission of information and the transfer of energy from one place to another.

## Electrical current

Students should have knowledge and understanding of the following content.

Content Additional guidance and suggested TDAs Specification reference GCSE Combined Science: Trilogy Specification reference GCSE Combined Science: Synergy
Outcome 1

Electric current is a flow of electrical charge. The size of the electric current is the rate of flow of electrical charge.

Electrical current is measured in amps using an ammeter.

6.2.1.2

4.7.2.1

The current through a component depends on both the resistance of the component and the voltage across the component. The greater the resistance of the component the smaller the current for a given voltage across the component.

Voltage is measured in volts using a voltmeter.

The term ‘potential difference’ will not be used.

6.2.1.3

4.7.2.2

The resistance of a component is a measure of how difficult it is for an electric current to pass through it.

Calculations of resistance will not be required, nor will the units of resistance.

Suggested activity for TDA Investigate which materials are the best electrical conductors.

6.2.1.3

4.7.2.2

Outcome 2

A complete circuit is necessary for a current to flow.

Cells and batteries supply current that always passes in the same direction. This is called direct current (d.c.).

No distinction between series and parallel circuits needs to be made.

The use of conventional circuit diagram symbols will not be required.

6.2.2

4.7.2.5

An alternating current (a.c.) is one that changes direction. Mains electricity is an a.c. supply. In the UK it has a frequency of 50 Hz and is 230 V.

6.2.3.1

4.7.2.5

## Domestic electricity

Students should have knowledge and understanding of the following content.

Content Additional guidance and suggested TDAs Specification reference GCSE Combined Science: Trilogy Specification reference GCSE Combined Science: Synergy
Outcome 3

Most electrical appliances are connected to the mains using a three-core flex.

The insulation covering each wire in the flex is colour-coded for easy identification:

• live wire – brown
• neutral wire – blue
• earth wire – green and yellow stripes.

The earth wire is a safety wire to stop the appliance becoming live and the fuse contains a thin piece of wire, which melts if the current becomes too large, thereby cutting off the supply.

Students should be able to select the correct fuse from a list when given the current rating of an appliance.

Some appliances do not have an earth wire because they are double insulated.

6.2.3.2

4.7.2.6

Outcome 4

Everyday electrical appliances are designed to bring about energy transfers.

The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance.

Students may be required to use the equation:

energy (kWh) = power (kW) x time (h)

6.4.4.2

4.7.2.8

## Magnetism and electromagnetism

Students should have knowledge and understanding of the following content.

Content Additional guidance and suggested TDAs Specification reference GCSE Combined Science: Trilogy Specification reference GCSE Combined Science: Synergy
Outcome 5

The poles of a magnet are the places where the magnetic forces are strongest. When two magnets are brought close together they exert a force on each other. Two like poles repel each other. Two unlike poles attract each other. Attraction and repulsion between two magnetic poles are examples of non-contact force.

The patterns of magnetic fields between bar magnets will be required.

6.7.1.1

4.6.3.1

Outcome 6

When a current flows through a conducting wire a magnetic field is produced around the wire.

The strength of the magnetic field depends on the current through the wire and the distance from the wire.

Shaping a wire to form a solenoid increases the strength of the magnetic field created by a current through the wire. Adding an iron core increases the magnetic field strength of a solenoid. An electromagnet is a solenoid with an iron core.

Students should be familiar with common uses of electromagnets, eg in scrapyard cranes and relays.

Suggested activity for TDA Investigate factors that affect the strength of an electromagnet.

6.7.2.1

4.6.3.4

## Different types of waves

Students should have knowledge and understanding of the following content.

Content Additional guidance and suggested TDAs Specification reference GCSE Combined Science: Trilogy Specification reference GCSE Combined Science: Synergy
Outcome 7

Waves may be either transverse or longitudinal.

In a transverse wave the oscillations are perpendicular to the direction of energy transfer. The ripples on a water surface are an example of a transverse wave.

In a longitudinal wave the oscillations are parallel to the direction of energy transfer. Longitudinal waves show areas of compression and rarefaction. Sound waves travelling through air are longitudinal.

Students should be able to identify whether a wave is longitudinal or transverse from a given diagram.

6.6.1.1

4.1.4.1

Outcome 8

Waves are described by their amplitude, wavelength and frequency.

The amplitude of a wave is the maximum displacement of a point on a wave away from its undisturbed position.

The wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave.

Students may be required to use the equation:

wave speed (m/s) = frequency (Hz) x wavelength (m)

The frequency of a wave is the number of waves passing a point each second.

Students should be able to identify wavelength and amplitude on a given diagram.

6.6.1.2

4.1.4.2

## Electromagnetic waves

Students should have knowledge and understanding of the following content.

Content Additional guidance and suggested TDAs Specification reference GCSE Combined Science: Trilogy Specification reference GCSE Combined Science: Synergy
Outcome 9

Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber.

Students will not be required to memorise the values of the wavelength or frequency of these waves.

6.6.2.1

4.1.4.3

Electromagnetic waves form a continuous spectrum and all types of electromagnetic wave travel at the same velocity through a vacuum (space) or air.

The waves that form the electromagnetic spectrum are grouped in terms of their wavelength and their frequency.

Going from long to short wavelength (or from low to high frequency) the groups are:
• microwave
• infrared
• visible light (red to violet)
• ultraviolet
• X-rays
• gamma rays.

Ultraviolet waves, X-rays and gamma rays can have hazardous effects on human body tissue. The effects depend on the type of radiation and the size of the dose.

Suggested activity for TDA Testing visual acuity in different colours of light.

6.6.2.1

4.1.4.3

Outcome 10

Electromagnetic waves have many practical applications, eg:

• microwaves – satellite communications, cooking food
• infrared – electrical heaters, cooking food, infrared cameras
• visible light – fibre optic communications
• ultraviolet – energy efficient lamps, sun tanning
• X-rays – medical imaging and treatments
• gamma rays – for sterilising.

Students should be able to give brief explanations of why each type of electromagnetic wave is suitable for the practical application.

Suggested activity for TDA Investigate the shielding of a mobile phone or remote control device.

Suggested activity for TDA Investigate the range over which a Bluetooth device is effective.

6.6.2.4

4.1.4.3