Efficiency of Machines Flashcards
What is efficiency the measure of?
How much energy is usefully transferred
What is the input energy of an electrical device e.g. a television?
What are it’s output energies?
Electrical energy
- Sound energy
- light energy
- thermal energy
What is the input energy of a battery?
What are it’s output energies?
Chemical energy
- Electrical energy
- Thermal energy
What is the input energy of electrical generation e.g. wind turbines?
What are it’s output energies?
Kinetic energy
- Electrical energy
- Thermal energy
What is the input energy of potential energy e.g. firing a bow and arrow?
What are it’s output energies?
Elastic potential energy
- Kinetic energy
- Thermal energy
Most energy transfers involve some ____, often as ____ ____
Most energy transfers involve some losses, often as thermal energy
The less energy is ‘wasted’, the more ____ a device is said to be
The less energy is ‘wasted’, the more efficicent a device is said to be
Define a ‘macine’
A machine is a device which turns one type of energy into another
What is the formula for energy efficiency?
Efficiency = Useful energy out / Total energy in
What is the formula for power efficiency?
Efficiency = Useful power out / Total power in
(exactly the same as energy efficiency)
What 2 ways can you give efficiency in the form of?
- A decimal
- A percentage
What are the formula triangles for energy and power efficiency?
Is any device 100% efficient?
No - not usually
What is wasted energy usually spread out as?
Thermal energy (heat)
What is the exception to no device being 100% effecient?
Electric heaters - all the electricity is converted into thermal energy (‘useful’ energy)
What, ultimately all energy end up as?
Thermal energy
If you use an electric drill, you get ____ ____ of energy, but they all quickly end up as ____ ____
If you use an electric drill, you get various types of energy, but they all quickly end up as thermal energy
What is useful energy?
Concentrated energy
How does thermal energy make the energy less concentrated?
The thermal energy is transferred to the cooler surroundings, which then beome warmer. As the thermal energy is transferred to cooler surroundings, the energy becomes less concentrated - it dissipates
The total amount of energy stays the same. The energy is still there, but as it becomes increasingly spread out, it can’t easily be used or collected back in again
When a questions asks ‘why is the input energy more than the (useful) output energy’, what do you answer?
Because some energy is wasted as heat
