Usefulness of Electrical Devices

• energy is measured in joules (J)
• power is the reat of energy transfer. power = energy transfered/time
• power is measured in watts (W)
• one watt is an energy transfer of one joule per second (J/s)
• example
• a kettle transfers 6000 J of energy in 3 secs
•        6000/3= 2000W or 2kW
• work is a name for energy transfer, therefore the formula for power can also be written as power= work/time
• current = rate of flow of electrons
• volatage = joules per coulomb of energy
• electrical power = voltage x current (P=IV)

energy transfered (kWh) = power (kW) x time (h)

kilowatt-hours are also known as units

example a 2000W electric fire is used for 3 hours. what is the cost at 8p per unit?

energy transferred = 2kW x 3 hours = 6kWh (6 units)

6 x 8 = 48p