5.4 Power And Efficiency Flashcards
1
Q
Define power
A
The rate at which 1 j of energy is transferred / rate of energy transferred
2
Q
State the relationship between power, work done and time
A
Power = work done / time
3
Q
Define 1 watt
A
1 joule per second
4
Q
State the 2 equations for calculating efficiency
A
Efficiency = useful output energy / total input energy
Efficiency = useful power output / total energy input
5
Q
Why are energy transfers in the real world never 100% efficient
A
Work done against resistive forces ( e.g. friction, air resistance ) means that some energy is always transferred to the thermal energy stores of the object and its surroundings
