Energy Loss
- Unintended or wasted energy transfers are inevitable
- There is no such thing as a perfect energy transfer
- Most wasted energy transfers result in heating of the objects and the surroundings
- We say this energy is dissipated (spread out) to the thermal store of the surroundings
- Work done against air resistance, frictional forces, and resistance in wires all result in heating
- That energy is transferred to the thermal store of the surroundings increasing the temperature of the air particles and surrounding objects
- Once energy is in the thermal store of the surroundings, it can not be 'gathered' for any specific use
- Therefore, it is referred to as wasted energy
Example 1: An Electric Kettle Boiling Water
- Useful energy transfer
- Energy is transferred by heating from the thermal store of the heating element in the kettle to the thermal store of the water
- Unuseful energy transfers
- Energy is transferred from the thermal store of the water to the thermal store of the kettle casing
- Energy is transferred from the thermal store of the kettle casing to the thermal store of the surroundings and the temperature of the air in the room will increase slightly
- Energy is transferred from the thermal store of the water to the thermal store of the surroundings as water evaporates
Example 2: An Electric Circuit Lighting a Filament Bulb
- Useful energy transfers
- Energy is transferred from the chemical store of the bulb to the thermal store of the filament wire (the fact that the filament wire glows hot is how the light is produced)
- Energy is transferred from the thermal store of the filament wire to the thermal store of the surroundings by radiation as visible light (EM radiation)
- Unuseful energy transfers
- Energy is transferred from the chemical store of the cell to the thermal store of the wires due to resistance
- Energy is transferred from the chemical store of the cell to the thermal store of the bulb casing (the metal and glass that make up the bulb)
- Energy is transferred from the thermal store of the filament wire to the thermal store of the surroundings (most of the energy transferred away from the bulb is by heating rather than as light)
Examiner Tip
Make sure you are able to identify different types of "useful" and "wasted" energy as this is commonly tested in exams!