3 - My Property

We use a range of electrical appliances in our homes on a daily basis and as a result many families have to budget carefully to cover the cost of electricity bills. Many appliances work using electromagnetic waves. Electrical and electronic engineers work to ensure that our appliances are efficient and that they are safe to use.

3.1 The cost of running appliances in the home

Candidates need to understand that:

It is useful for energy consultants to be able to compare the running costs of different electrical appliances in our homes. Energy is used for heating and to power electrical appliances in the home. Electrical appliances transfer energy. The rate at which the energy is transferred in an electrical appliance is called the power.

Energy labels help consumers work out which appliances are most efficient and cost-effective.

Candidates need to:

1. Know that energy is normally measured in joules and that 1 watt = 1 joule/second.

2. Calculate the power consumed by an electrical appliance using the formula:

Power (watts) = potential difference (volts) × current (amps)

3. Carry out simple calculations for different electrical appliances in the home using the formula:

Power (kilowatt, kW / watts, W) = energy transferred  (kilowatt-hour, kWh / joules) ÷ time (hours, h / seconds, s)

4. Interpret the readings taken from a domestic electricity meter and know that a unit of electricity = 1 kWh.

5. Calculate the costs of using different electrical appliances using:

Total cost = number of kilowatt-hours × cost per kilowatt-hour.

6. Interpret information from energy labels on appliances and know why this is useful.

7. Draw and interpret Sankey diagrams that show the types of energy transferred by an electrical appliance.

8. Explain the meaning of the term ‘efficiency’ when applied to simple energy transfers in electrical appliances, and give reasons for energy losses in appliances.

9. Calculate the efficiency of an appliance using the equations:

efficiency = total energy in / useful energy out

efficiency = total power in / useful power out

Within this context, candidates should be able to use scientific data and evidence to discuss, evaluate or suggest implications of the following:

■ the efficiency of different appliances used in the home

■ the costs of running home appliances.

3.2 Electromagnetic waves in the home

Candidates need to understand that:

Electronic engineers use electromagnetic radiation for radio, mobile phones, and cable and satellite television.

Waves transfer energy from a source to other places without any matter being transferred.

The various types of electromagnetic radiation form a continuous spectrum from high frequency (short wavelength) gamma rays to low frequency (long wavelength) radio waves. The uses of different types of electromagnetic radiation depend on these and other properties. Home owners are often concerned about the risks of using devices such as mobile phones that rely on electromagnetic waves.

Candidates need to:

1. Know that electromagnetic radiation travels as waves and moves energy from one place to another.

2. Know that the number of waves per second produced by a source is called the frequency and is measured in hertz (Hz).

3. Know the order of the electromagnetic spectrum, from radio waves (low frequency/long wavelength) to gamma rays (high frequency/short wavelength).

4. Know that the higher the frequency of the wave the higher the energy.

5. Use the equation:

velocity (m/s) = frequency (Hz) × wavelength (m).

6. Name and describe the uses of the different types of electromagnetic waves used in our homes:

(a) radio waves – TV and radio

(b) microwaves – mobile phones, satellite TV and cooking

(c) infrared – remote controls for TV and DVD players

(d) visible light – fibre optic cables

(e) UV – sun beds.

7. Know that X-rays and gamma rays are not usually used in the home as they can damage the body, but can be used in medicine for X-rays and radiotherapy.

Within this context, candidates should be able to use scientific data and evidence to discuss, evaluate or suggest implications of the following:

■ how the uses of different types of waves depend on their properties

■ the dangers of using electromagnetic waves for various purposes, eg sun beds, mobile phones and microwave cookers.

Suggestions for practical work that could be used to support Theme 3

It is the responsibility of the centre to be aware of the health and safety implications of any practical work and to ensure that risk assessments for practicals are carried out.

■ Construct a model house, using sensors and data loggers to measure temperatures with and without various types of insulation.

■ Investigate how the efficiency of an electric motor varies with the load.

■ Candidates read the electricity meter at home on a daily or weekly basis (with permission from their parents). They could then look for trends in usage and try to explain these, for example, in terms of weather conditions.

■ Demonstrate the use of an electrical joulemeter to investigate the energy transferred by low-voltage lamps of different powers, and by low-voltage motors and low-voltage immersion heaters.

■ Investigate the efficiency of low-voltage bulbs – invert in water and measure temperature change.

■ Use a class set of skipping ropes to investigate frequency and wavelength.

■ Carry out traditional experiments with a slinky spring.

■ Carry out traditional investigations using ripple tanks, including the relationship between depth of water and speed of wave.