1. ASSIGNMENT BOOK Unit 8 Part 1 8.10 & 8.11 8.10 Power of an Electrical Appliance & 8.11 Cost of Electricity A.Check your concepts Study each of the following statements. Put a ‘T’ in the box against a correct statement and a ‘F’ against an incorrect statement. T T 1.Power is measured in watts (W). 2.Appliances with a larger power rating have a larger operating current. E E

2. ASSIGNMENT BOOK Unit 8 Part 1 8.10 & 8.11 F T 3.One kilowatt is also called ‘one unit of electricity’. 4.Electrical energy consumed at our homes is measured by a kilowatt-hour meter. E E

3. ASSIGNMENT BOOK Unit 8 Part 1 8.10 & 8.11 B. Questions 1.82 A 18.2 A 2 A AppliancePower ratingOperating current Desktop computer Electric water heater Car lamp 220 V, 400 W 220 V, 4000 W 12V, 24W 1.Calculate the operating currents for the following appliances. (3 marks) E

4. ASSIGNMENT BOOK Unit 8 Part 1 8.10 & 8.11 3,600,000 1,080,000 540,000 1 0.3 0.15 $ 0.9 $ 0.27 $ 0.135 Electric water heater Table lamp Computer AppliancePower Operating time 4000 W 100 W 300 W 15 mins 3 hours 30 mins Amount of electrical energy consumed (J) Amount of electrical energy consumed (kW h) Cost of electricity ($) 2.The power of an appliance shows the amount of electrical energy transferred to it per second. Try to complete the following table. (9 marks) Given: 1 kW h = 3,600,000 J 1 kW h of electricity costs $ 0.9 E

5. ASSIGNMENT BOOK Unit 8 Part 1 8.10 & 8.11 ‘220 V, 1600W’ electric oven ‘220 V, 900W’ electric iron ‘220 V, 1100W’ Vacuum cleaner three-pin plugs ON / OFF switch 15 A cable 3. Three three-pin plugs are plugged into an extension unit as shown below. The extension unit has an ON/OFF switch and is installed with a 15 A fuse. One plug is connected to a ‘220 V, 1100 W’ vacuum cleaner, another is connected to a ‘220 V, 900 W’ electric iron and the third one is connected to a ‘220 V, 1600 W’ electric oven. (3 marks) E

6. ASSIGNMENT BOOK Unit 8 Part 1 8.10 & 8.11 (a) Are the appliances connected in series or in parallel?_____________________ (1 mark) (b) Calculate the operating currents of the three appliances. (3 marks) Operating current of the vacuum cleaner = _____________________________________ Operating current of the electric iron = _____________________________________ Operating current of the electric oven = _____________________________________ in parallel 1100 / 220 = 5 A 900 / 220 = 4.1 A 1600 / 220 = 7.3 A

7. ASSIGNMENT BOOK Unit 8 Part 1 8.10 & 8.11 (c)What would be the current flowing through the 15 A cable if all three appliances were switched on together? (1 mark) _____________________________________ (d)What would happen if all three appliances were switched on together? (1 mark) _____________________________________ Current = 5 + 4.1 + 7.3 = 16.4 A The 15 A fuse would melt and break the circuit.

8. ASSIGNMENT BOOK Unit 8 Part 1 8.10 & 8.11 (e)This is called __________________ and should be avoided. (1 mark) (f)What would happen if the block did not have the 15 A fuse? (1 mark) _____________________________________ _____________________________________ overloading The 15 A cable will become very hot and it may result in a fire.