Define power. State the difference between $1$ watt and $1$ watt hour. Establish the relationship between the commercial unit of electric energy and the $SI$ unit of energy. An electric heater rated $1000 \ W / 220 \ V$ operates for $2$ hours daily. Calculate the cost of energy to operate it for $30$ days at the rate of ₹ $5.00$ per $kWh$.

(N/A) Power is defined as the rate at which electric energy is dissipated or consumed in an electric circuit.
$1$ watt is the power consumed by a device that carries a current of $1 \ A$ when operated at a potential difference of $1 \ V$, whereas $1$ watt hour is the amount of energy consumed when $1$ watt of power is used for $1$ hour.
The commercial unit of electric energy is $kWh$.
$1 \ kWh = 1000 \ W \times 3600 \ s = 3.6 \times 10^6 \ J$.
Total energy consumed by the heater in $30$ days:
$E = \text{Power} \times \text{Time} \times \text{Days} = 1000 \ W \times 2 \ h \times 30 = 60000 \ Wh = 60 \ kWh$.
Cost of energy = $60 \ kWh \times ₹ 5.00/kWh = ₹ 300$.