Paying for Electricity

L.O. You will be able to define the unit of PowerYou will be able to recall that energy from the mains is

measured in kWh (kilowatt-hours) You will be able to calculate the power and energy used

and the cost of that that energy

Starter

Re-capDefine these terms1 Primary Coil2 Secondary Coil3 Slip Rings

Keywords activity

1 Look at your cards, there are six Keywords and 12 definitions. Match each word to 2 definitions.

2 Lay them out as you think they ought to be3 Let’s check4 Stick them into your book

How much Energy?

1 What is the power rating of a toaster that uses 68,000 Joules in 40 seconds?

2 What is the power rating of a electric blanket that uses 450,000 J in 7,200 seconds?

3 What is the power rating of a food mixer that uses 40,000 J in 2 min

4 What is the power rating of a TV that uses 90 kJ while watching Eastenders?

1 How much energy is used by a kettle with a power rating of 1200 W in 90 seconds?

2 How much energy is used by a electric fire with a power rating of 2000 W in 4 hours?

3 How long would it take a cooker with a power rating of 1800 W to use 600,000 Joules?

You use about 7,500,000 Joules a day, or 5,208 Joules a min or 87 Joules a second! Q If the toaster from Q1 was on all day how much energy would it use?

How much power?You can work out the power of a device from the Current and the Voltage

1 A laptop uses 19 Volts which is supplied by 3.5 A current. What is the power of the laptop?

2 A Hoover uses 230 Volts which is supplied by 9 A current. What is the power of the Hoover?

3 A oven uses 230 Volts which is supplied by 12 A current. What is the power of the oven?

1 A radio uses a 9V battery and has a power rating of 18 W. How much current is the radio drawing (Using)?

2 A toastie maker uses a 230V and has a power rating of 1800 W. How much current is it drawing (Using)?

3 A radio has a power rating of 18 and the current is 2A. What is the voltage of the supply?

4 A toastie maker has a power rating of 1800 W and a current of 7.83A. What is the Voltage?

How much does it cost?(Other than The Earth!)

1 Electricity costs 15p per kWh how much does it cost to run a TV with a power rating of 25W for the duration of Top Gear?

2 Electricity costs 7p per kWh. How much does it cost to cook a roast dinner (2 hours cooking time) if your oven has a power rating 2000W?

3 You are having a party that will last 3 hours. Your stereo has a power rating of 70W. If electricity costs 10p per kWh, how much money will your parents spend?

4 Now do questions 4 and 5 from page 263.

1 What is the cost if the P = 400 W, t = 3hrs and cost per kWh = 9p?

2 Cost if P = 500 W, t = 2hrs and cost per kWh = 20p

3 Cost if P = 2000 W, t = 4hrs and cost per kWh = 8p

4 Cost if P = 1 kW, t = 2hrs and cost per kWh = 15p

5 Cost if P = 900W, t = 30 min and cost per kWh = 7p

Smart Meters, why?

• Look at Q 7 Page 263• Discuss your ideas with your partner• Make notes on your under these headings Work to be done / Ease of use / Disadvantages (What don’t you know)?

Let’s discuss• Make notes on your work• Now try to answer Q7 as fully as possible • Remember we are looking for 6 marks so use try to use

the vocabulary and think about spelling and punctuation

Plenary