Efficiency of Machines Flashcards
1
Q
Efficiency =
A
useful energy out (divided by) total energy in
2
Q
Why is no device 100% efficient?
A
there is always wasted energy, it is usually spread out as heat
3
Q
What happens to the wasted heat energy ?
A
it is absorbed into its surroundings
4
Q
In an energy transformation diagram what does the thickness of the arrow represent?
A
the amount of energy
5
Q
The units of energy are…
A
Kilowatt-hours (kWh)
6
Q
Power is usually measured in…
A
watts (W) or kilowatts (kW)
7
Q
Energy is usually measured in…
A
joules (J)
8
Q
A kilowatt-hour is…
A
the amount of electrical energy used by a 1 kW appliance left on for 1 hour
9
Q
the amount of energy transferred by an appliance depends on:
A
- its power
- amount of time its switched on
10
Q
No. of UNITS (kWh) used =
A
POWER (in kW) x TIME (in hours)
11
Q
COST =
A
No. of UNITS x PRICE per unit
