Power Flashcards
What is the definition of ‘Power’?
The rate at which energy is transferred
or rate at which work is done
State two equations for power. Give SI units for all
quantities involved.
power = energy transferred / time
power = work done / time
Energy (J), Work Done (J), Time (s)
What is the unit of power?
Watt (W)
What is one Watt equivalent to?
1 Joule per second (J/s).
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 of Motor B.
Which dissipates the most power?
Motor A.
The energy transferred is the same but
the time taken is less (P=E/t).
What is efficiency?
The proportion of energy that is
converted usefully, rather than
wasted/dissipated.
How do you calculate efficiency?
Efficiency = useful energy out / total energy in
What are the units of efficiency?
Efficiency is a ratio so has no units, but it
can be expressed as a percentage.
