A battery transfers stored chemical energy as charged particles called electrons, typically moving through a wire. For example, electrical energy is transferred to the surroundings by the lamp as light energy and thermal (heat) energy.
Lightning is one good example of electrical energy in nature, so powerful that it is not confined to a wire. Thunderclouds build up large amounts of electrical energy. This is called static electricity. They are released during lightning when the clouds strike against each other.
Electrical energy can be used to turn electric motors which can lift things or make things to move. We can use it to produce heat in kettles or ovens. It can be produced by a machine called dynamo or generator. A bicycle dynamo can be seen below.
All electrical equipment has a power rating, which indicates how many joules of energy are supplied each second. The unit of power used is the watt(W). Light bulbs often have power rating of 60W or 100W. Electric kettles have rating of about 2000W. A 2kW kettle converts 2000J of energy each second.
The power of a piece of electrical equipment depends on the voltage and the current.
P= V I …………….. (1)
where, P- power in watts(W)
V- voltatge in volts(V)
I- current in amperes(A)
The energy transferred by an appliance depends on the power rating and the time the appliance is running.
E = Pt………………….. (2)
where, E- energy in joules(J)
P- power in watts(W)
t – time in seconds(s)
Therefore, E = VIt ……………………..(3) (since P= VI)