Electrical Power & Mains Electricity

Energy from power and time

E = P × t

• where:
  • E = energy transferred (J)
  • P = power of the device (W)
  • t = time the device runs for (s)
• Substituting P = I × V gives a second form that uses circuit quantities directly:

E = I × V × t

• The two equations are equivalent, so pick whichever set of quantities the question hands you

Energy and work

• The work done by the charge flowing through a component is exactly the energy transferred to that component
• In a complete circuit, the total energy delivered by the battery equals the total energy transferred to every component on the loop, which is conservation of energy