Electrical appliances
There are many electrical appliances that are used in the home to transfer electrical energy to other useful forms.
| Appliance | Useful energy | Wasted energy |
| Electric kettle | Energy that heats the water. | Internal (thermal) energy heating the kettle. Infrared radiation lost to the surroundings. |
| Hair dryer | Internal (thermal) energy heating the air. Kinetic energy of the fan that blows the air. | Sound radiation. Internal (thermal) energy heating the hairdryer. Infrared radiation lost to the surroundings. |
| Light bulb | Light radiation given out by the hot filament. | Infrared radiation lost to the surroundings. |
| TV | Light radiation that allows the image to be seen. Sound radiation that allows the audio to be heard. | Internal (thermal) energy heating the TV set. Infrared radiation lost to the surroundings. |
| Appliance | Electric kettle |
|---|---|
| Useful energy | Energy that heats the water. |
| Wasted energy | Internal (thermal) energy heating the kettle. Infrared radiation lost to the surroundings. |
| Appliance | Hair dryer |
|---|---|
| Useful energy | Internal (thermal) energy heating the air. Kinetic energy of the fan that blows the air. |
| Wasted energy | Sound radiation. Internal (thermal) energy heating the hairdryer. Infrared radiation lost to the surroundings. |
| Appliance | Light bulb |
|---|---|
| Useful energy | Light radiation given out by the hot filament. |
| Wasted energy | Infrared radiation lost to the surroundings. |
| Appliance | TV |
|---|---|
| Useful energy | Light radiation that allows the image to be seen. Sound radiation that allows the audio to be heard. |
| Wasted energy | Internal (thermal) energy heating the TV set. Infrared radiation lost to the surroundings. |
The greater the amount of the supplied electrical energy that the appliance transfers to useful energy stores, the more efficient the device will be. This can be shown in an energy transfer diagram.
Example
A kettle will transfer the supplied electrical energy to both useful and wasted energy stores. The useful energy store will heat the water and the wasted energy stores will be dissipated to the surroundings.
As efficiency is calculated using the equation:
\(efficiency = \frac{useful~power~transferred}{total~power~supplied}\)
\(efficiency = \frac{180,000}{200,000}\)
\(efficiency = 0.9\)
Question
What are the useful and wasted stores of energy for a washing machine?
Useful stores - kinetic energy of the drum, internal (thermal) energy of the water.
Wasted stores - sound radiation and infrared radiation dissipated to the surroundings.
