Unit 4 Electricity and magnetism
Notes
Since power is related to voltage and current (P=IV) and energy is related to power and time, E=Pt can be rewritten as:
E=IVtE=energy (J)
I=current (A)
V=voltage (V)
t=time (s)
We simply substitute IV for P to get the formula above.

ExampleCalculate the energy transferred by a 12V hairdryer, running on a current of 0.50A, that is left on for 8.0 minutes.
Step 1 List all the information in symbol form and change into appropriate and consistent SI units if required.
V=12V
I=0.5A
t = 8.0 minutes = 8 × 60 = 480s t=8.0 minutes=8 × 60=480s
E=?
Step 2 Use the correct formula.
E=IVt
Step 3 Calculate the answer by putting the numbers into the formula.
E = IVt = 0.5 × 12 × 480 = 2880J E=IVt=0.5 × 12 × 480=2880J
ALWAYS REMEMBER TO STATE THE UNIT FOR CALCULATED QUANTITIES.