1. Cost of electricity Objectives Be able to calculate the cost of electrical devices. HSW: AF2: Evaluate the effects of technological developments on society as a whole. Used before in:Will use again in: PLTS: Team Workers: collaborate with others to work towards a common goal. Used before in:Will use again in: 15 October, 2015 Keywords Power, Watt, Energy, Joules, Work Done, Kilowatt, Kilojoules, kWhour, Unit.

2. Outcomes All students should be able to: Calculate the number of units used by a an electrical appliance. Most students should be able to: Calculate the cost of using an electrical appliance of a certain power rating for a specific time. Some students should be able to: Read electricity bills and compare estimates to bills and different tariffs.

3. Power What is power? Power is the energy transferred in a certain time. Power in Watts is the amount of Joules transferred in 1 second. ENERGY POWER ¦ TIME

4. Power Challenge. Use the dynamo connected to the dynamo to measure the energy transferred by 2 students over different amounts of time. Record the results in a table. Calculate who has the biggest average power. NameEnergy (J)Time (s)Average Power (W)

5. Calculating the cost of electricity Clearly, this depends on two things: the POWER RATING of the appliance and HOW LONG you leave it on for. Electricity is measured in “units”, also called “kilowatt hours” (kWh). To work out how much something would cost use two steps: 1)Find out how many units have been used: No. of units = Power rating x Time appliance is on for in kWh in kWin hours 2) Multiply the number of units by how much each one costs: Cost of electricity = no. of units used x cost of each unit in pencein kWhin pence

6. Units of Electricity Electricity is measured in units called “kilowatt hours” (kWh). For example… A 3kW fire left on for 1 hour uses 3kWh of energy A 1kW toaster left on for 2 hours uses 2kWh A 0.5kW hoover left on for 4 hours uses __kWh A 200W TV left on for 5 hours uses __kWh A 2kW kettle left on for 15 minutes uses __kWh

7. The Cost of Electricity To work out how much a device costs we do the following: Cost of electricity = Power (kW) x time (h) x cost per kWh (p) For example, if electricity costs 8p per unit calculate the cost of the following… 1)A 2kW fire left on for 3 hours 2)A 0.2kW TV left on for 5 hours 3)A 0.1kW light bulb left on for 10 hours 4)A 0.5kW hoover left on for 1 hour 48p 8p 4p

8. Demo Time!! The cost of lighting a home. Can you calculate the cost of lighting your home for 1 day? 1 month? 1 year?

9. Electrical Power As a class we will now do questions from Milner Text book p 20-21. In pairs do questions on p22-23. Time Limit: 15 mins. Peer mark.

10. Plenary – Snowball – The Big Q: Why Be Energy Efficient? In the back of your books jot down 3 ideas – why we should be energy efficient. Now discuss your ideas with your partner. Now talk in groups to see if you have all said the same things or not – In 2 minutes your teacher will pick on one of you to tell the rest of the group your ideas, so get involved!

11. Plenary - Hotseat 1 person sits at the front on the “hotseat” Your teacher has a list of questions from the lesson we have done. Answer 3 correctly – get a merit and choose the next person.