# Uses and cost of electricity

A **current** flowing through a wire or any other conductor causes **heating ** of the wire. Electrical energy is converted into ** thermal energy ** due to the **resistance** of the wire.

An electric kettle converts electrical energy into thermal energy to boil water.

A conductor with **high resistance** converts more electrical energy into thermal energy than a conductor with **low resistance**.

The heating elements in many home appliances (e.g. electric ovens, water heaters) are made of nichrome because it has a high resistance relative to other metals.

A large proportion of the **electrical energy** passing through it is converted into **thermal energy**.

One kilowatt hour is the total energy consumed when an appliance with a power of $$1\text{ kW}$$ ($$1000\text{ W}$$) is used continuously for $$1\text{ h}$$.

A kilowatt hour is a unit of **energy** like the joule. The kilowatt hour is frequently used in everyday life (such as on energy bills), while the joule is the SI unit for energy and is used in a scientific context.

The kilowatt hour is the product of units of power (kilowatt, energy per time) and time ($$1 \text{ kW}\times 1 \text{ h} = 1 \text{ kW h}$$).

A washing machine with a power of $$\Tred{500 \text{ W}}$$ is used for $$\Tblue{2 \text{ hours}}$$. The energy it consumes is equal to $$\Tred{0.5 \text{ kW}} \times \Tblue{2 \text{ hours}} = 1 \text{ kW h}. $$

Electricity companies charge for the usage of electricity in terms of **dollars (or other currencies) per kilowatt hour ($$\$/ \text{kW h}$$)**.

The ** cost ** of using an electrical appliance is given by: $$$\begin{align*}\Tgreen{\text{total cost}} =& \text{power in kilowatts } \times \text{time in hours} \\ & \times \text{cost per kilowatt hour}\end{align*}$$$

A light bulb with a power of $$ 100 \text{ W}$$ is used for $$10 \text{ h}.$$ The cost of electricity is $$\$ \, 0.15 \, / \text{ kW h}$$.

The ** cost ** of using the light bulb is: $$$0.1 \text{ kW} \times 10 \text{ h} \times \$ \, 0.15 \, / \text{ kW h} = \Tgreen{\$ \, 0.15} = \Tgreen{15 \text{ c}}$$$