topic 8

Subdecks (1)

what is power 
the rate at which energy is transferred
state 2 equations for power
power = energy transferred / time , power = work done / time
what are the units for work done and energy 
j
what is the unit of power
watt
what is one watt equivalent to
1 joule per second
what does a power rating of 10w mean for an electrical device
it converts 10 joules of energy every second
two motors lift the same mass through the same height , motor a does this in half the time that motor b does , which disspiates the most power
motor a as it took less time but the same amount of energy is transferred
what is efficiency  
the proportion of energy that is converted usefully , rather than wasted / dissipated
how do you calculate efficiency
useful energy out / total energy in
what are the units for efficiency
efficiency is a ratio so it has no units , bbut it can be expressed as a percentage