Electrical appliances
Many electrical appliances used in the home transfer electrical The capacity for doing work. to other useful forms.
| Appliance | Useful energy | Wasted energy |
| Electric kettle | Energy that heats the water. | Thermal energy store heating the kettle. Infrared radiation transferred to the surroundings. |
| Hairdryer | Thermal energy store heating the air. Kinetic energy of the fan that blows the air. | Sound radiation. Thermal energy store heating the hairdryer. Infrared radiation transferred to the surroundings. |
| Light bulb | Light radiation given out by the hot filament. | Infrared radiation transferred to the surroundings. |
| TV | Light radiation that creates images for the user. Sound radiation that creates audio for the user. | Thermal energy store heating the TV set. Infrared radiation transferred to the surroundings. |
| Appliance | Electric kettle |
|---|---|
| Useful energy | Energy that heats the water. |
| Wasted energy | Thermal energy store heating the kettle. Infrared radiation transferred to the surroundings. |
| Appliance | Hairdryer |
|---|---|
| Useful energy | Thermal energy store heating the air. Kinetic energy of the fan that blows the air. |
| Wasted energy | Sound radiation. Thermal energy store heating the hairdryer. Infrared radiation transferred to the surroundings. |
| Appliance | Light bulb |
|---|---|
| Useful energy | Light radiation given out by the hot filament. |
| Wasted energy | Infrared radiation transferred to the surroundings. |
| Appliance | TV |
|---|---|
| Useful energy | Light radiation that creates images for the user. Sound radiation that creates audio for the user. |
| Wasted energy | Thermal energy store heating the TV set. Infrared radiation transferred to the surroundings. |
The greater the amount of the supplied electrical energy transferred to useful energy stores, the more efficient the device will be. This can be shown in an energy transfer diagram or A diagram showing the flow of energy in a process. The width of the arrows indicates the relative amounts of energy involved..
Sankey diagrams
Sankey diagrams show the energy transfers in a system:
- the energy transferred into the system is shown as an arrow
- this arrow splits into narrower arrows showing other transfers
Sankey diagrams are most useful when the amount of energy in each of the energy sources is known. The width of the arrow is drawn to scale to show the amount of energy.
Thermal conductivity
The A measure of how well a material conducts energy when it is heated. of a material is a measure of how quickly energy transfers through it by heating.
- a material with a high thermal conductivity transfers energy quickly
- a material with a low thermal conductivity transfers energy slowly, and may be used as a thermal Material that does not allow charge or heat to pass through it easily.
A building with walls of a high thermal conductivity will cool down faster than one with walls of a low thermal conductivity. The graph shows an example of this difference.
Reducing unwanted energy transfer
There are two main ways to reduce unwanted energy transfers by heating:
- use insulator - materials with low thermal conductivity
- use thicker materials
The table shows some ways in which this is achieved in homes and other buildings.
| Method | Details |
| Cavity wall | A gap between two brick walls contains air, which has a lower thermal conductivity than brick. |
| Cavity wall insulation | The gap between two brick walls is filled with material that has a lower thermal conductivity than air. |
| Loft insulation | A thick layer of material with a low thermal conductivity reduces the rate of heat transfer through the ceiling. |
| Double glazed windows | A gap between two panes of glass contains air or another gas, which has a lower thermal conductivity than glass. |
| Method | Cavity wall |
|---|---|
| Details | A gap between two brick walls contains air, which has a lower thermal conductivity than brick. |
| Method | Cavity wall insulation |
|---|---|
| Details | The gap between two brick walls is filled with material that has a lower thermal conductivity than air. |
| Method | Loft insulation |
|---|---|
| Details | A thick layer of material with a low thermal conductivity reduces the rate of heat transfer through the ceiling. |
| Method | Double glazed windows |
|---|---|
| Details | A gap between two panes of glass contains air or another gas, which has a lower thermal conductivity than glass. |