• In mains electricity, current and voltage are varying all the time
• This also means the?power?varies constantly, recall the equations for power:

• Where:
  • I =?direct?? current (A)
  • V =?direct?voltage (A)
  • R = resistance (Ω)
• The?r.m.s?values means equations used for direct current and voltage can now be applied to?alternating current? and voltage
• These are also used to determine an?average?current or voltage for alternating supplies
• Recall the equation for?peak current:

• Therefore, the peak (maximum) power is related to the mean (average) power by:

• Therefore, it can be concluded that:

?The mean power in a resistive load is half the maximum power for a sinusoidal?alternating current or voltage

Mean power is exactly half the maximum power

Step 1:?Write down the known quantities

Resistance, R = 40 ?

Peak voltage,?V₀?= 240 V

Step 2:?Write out the equation for the peak power and calculate

Step 3:?Calculate the mean power

• • • • The mean power is?half?of the maximum (peak) power

Mean power = 1440 / 2 = 720 W