Name the unit in which you pay the cost of your electricity bill. How is it related to joule?

We pay the cost of our electricity bill in unit kWh (kilowatt hour).

Since,

$\text{Power} = \dfrac{\text{Energy}}{\text{Time}} \\[1em] \therefore \text{Energy} = \text{Power} \times \text{Time} \\[1em] \text{i.e. } \text{Energy (in kWh)} \\[1em] = \text{Power (in kWh)} \times \text{Time (in h)}$

Hence,

1 kWh = 1 kW x 1 h

= 1000 W x (60 x 60 s)

= 36,00,000 J

= 3.6 x 10⁶ J

So 1 kWh = 3.6 x 10⁶ J.