### Electricity Calculation: Online IGCSE Phyics Class

# Calculating Wat in the Electrical Consumption

The applications below are used in households. Find the amount of kWh usage for 5 hours. Give your

**Question 1:**

How much electrical energy in joules does a 100W lamp transfer in

1-second

5 seconds

1-minute

*Solution *

*a) 1600 x 1 = 100J*

*b) 100 x 5 = 500J*

*c) 100 x 60 = 6000J*

**Question 2**

What is the power of a lamp rated in 12V 2A

How many joules of electrical energy is transferred per second by a 6V 0.5A lamp

*Solution *

*Power = Voltage x Current = 12 x 2 = 24W*

*Energy = Voltage x Current x Time = 6v x 0.5 x 60 = 180W*

**Question 3**

What is the cost of heating a tank of water with a 3000W immersion heater for 80 minutes if electricity costs 10cents perkWh?

*Solution *

*3kW x 1.3hr x 10 = 39 cents*