- Created by: Alice Ugg-Boots
- Created on: 15-06-11 19:24
HELLO! I HAVE JUST LOST SIX PAGES OF VERY INTELLIGENT PHYSICS NOTES, AND I DO NOT HAVE TIME TO REPLACE THEM, SO IF YOU ARE LOOKING FOR INFORMATION ON HEAT CONDUCTION, CONVECTION, RADIATION AND HEAT OR ENERGY TRANSFER, HERE IS NOT THE PLACE.
AQA Core Physics 1a - Energy and Electricity.
Efficiency of Machines.
Most Energy Transfers Involve Some Losses, Often as Heat.
1) Useful devices are only useful because they can convert energy from one to another.
2) In doing so, some of the useful input energy is always lost or wasted, often as heat.
3) The less energy wasted, the more efficient the device is said to be.
4) The efficiency flow diagram is pretty much the same for all devices:
ENERGY INPUT ----> USEFUL DEVICE ----> USEFUL ENERGY OUTPUT.
-----> WASTED ENERGY AS HEAT/SOUND.
It's Really Simple to Calculate Efficiency...
A machine is a device which turns one type of energy into another.
The efficiency of a device is defined as:
Efficiency = Useful Energy Output / Total Energy Input.
How to Use The Formula:
1) You find out how much energy is supplied to a machine. (Total Energy Input.)
2) You find out how much useful energy the machine delivers. (Useful Energy Output.) An exam question either tells you this directly or tells you how much energy is wasted as heat/sound.
3) Either way, you get those two important numbers and then just divide the smaller one by the bigger one to get a value for efficiency somewhere between 0 and 1 or (or 0 and 100%).
4) The other way they might ask it is to tell you the efficiency and the input energy and ask for the energy output, so you need to be able to swap the formula around.
For any specific example you can give more detail about the types of energy being input or output. but remember this:
No device is 100% efficient and the wasted energy is always dissipated as heat.
Electric heaters are the exception to this. They're 100% efficient because all the electricity is converted into "useful" heat. Ultimately, all energy ends up as heat energy. If you use an electric drill, it gives out various types of energy but they all quickly end up as heat.
We Call It Wasted Heat Because We Can't Do Anything Useful With It.
1) Useful energy is concentrated energy. As you know, the entire energy output by a machine, both useful and wasted, eventually ends up as heat.
2) This heat is transferred to cooler surroundings, which then become warmer. As the heat is transferred to cooler surroundings, the energy becomes less concentrated, it dissipates (spreads out).
3) According to the Principle of the Conservation of Energy, the total amount of energy stays the same. So the energy is still there, but it can't be easily used or collected back in again.
Some Devices Are More Efficient than…