** Law of Conservation of Energy**

Energy can neither be created nor destroyed, it can only be transformed from one form to another. The total energy before and after transformation remains the same.

**Total energy = KE + PE**

**For example**: consider a ball falling freely from a height. At height h, it has only PE = mgh.

By the time it is about to hit the ground, it has a velocity and therefore has KE=

mv2. Therefore, energy gets transferred from PE to KE, while the total energy remains the same.

**Power (P)**

Power is defined as the rate of doing work or rate of transfer of energy.

Power = work/time

P=W/T

• Unit of power is watt (W).

Watt

**Commercial unit of energy**

• Kilowatt hour (kWh) or 1 unit

• The energy used in households, industries and commercial establishments are usually expressed in kilowatt hour.

• 1 kWh is the energy used in one hour (1 h) at the rate of 1000 J/s or (1 kW).

∴1 kWh =l kW x U = 1000 W x 3600 s = 3600000 J

1 kWh = 3.6 x 106 J = 1 unit

** Power** can also be represented as,

P = Fv

F = force applied

v = velocity of object

P=W/t=Fs/t=Fv