### Energy Consumption

#### Calculating the cost of electricity consumption

- The amount of electrical energy consumed in a given time:
- The larger the power rating in the electrical appliance, the higher energy is used for every second.
- The longer the usage time, the higher electrical energy is consumed.
- The cost of electricity consumption is based on the number of kilowatt-hours (kWh) of electrical energy used.
- The kilowatt-hours are sometimes known as the domestic units of electricity.
- The kilowatt-hour (kWh) is the energy used by a device at a rate of 1000 watts in one hour.
1 kWh = (1000 W) × (60 × 60 s) = 3.6 MJ

**Example**:

If TNB charges 22 cents for each kWh of electrical energy used, calculate the total cost of using a 2kW electric kettle for 15 minutes and a 20 W filament bulb for 8 hours.

**Answer**:

Electrical energy consumed by the kettle,

$$\begin{array}{l}{E}_{1}={P}_{1}{t}_{1}\\ {E}_{1}=(2kW)(\frac{15}{60}h)=0.5kWh\end{array}$$

Electrical energy consumed by the bulb,

$$\begin{array}{l}{E}_{2}={P}_{2}{t}_{2}\\ {E}_{1}=(0.02kW)(8h)=0.16kWh\end{array}$$

Total energy consumed,

$$\begin{array}{l}E={E}_{1}+{E}_{2}\\ E=0.5+0.16=0.66kWh\end{array}$$

$$Cost=0.66\times 22cent=14.52cent$$