Energy is Transferred from Cells to other Sources

• You know that a moving circuit transfers energy. This is because the charge does work against the resistance of the circuit

• Electrical Appliances are designed to transfer energy to components in the circuit when a current flows

• Of course, no appliance transfers all energy completely usefully. The higher the current, the more energy is transferred to the thermal energy stores of the components. You can calculate the efficiency of any electrical appliance

Energy transferred depends on the Power

• The total energy transferred by an appliance depends on how long the appliance is on for and its power

• The power of an appliance is the energy that is transfers per second. So the more energy it transfers on a given time, the higher its power

• The amount of energy transferred by electrical work is given by:

• Energy Transferred(J)= power(W) x time(s)

• Appliances are often given a power rating-they’re labelled with the maximum safety power that they can operate at. You can usually take this to be their maximum operating power

• The power rating tells you the maximum amount of energy transferred between stores per second when the appliance is in use

• This helps customers choose between models-the lower the power rating, the less electricity an appliance uses in a given time and so the cheaper it is to run

• But, a higher power doesn’t necessarily mean that it transfers more energy usefully. An appliance may be more powerful than another**, but less efficient,** meaning that it might still only transfer the same amount of energy to useful stores.