122 Chapter 6 • Electricity
5. Give four examples of situations where the heating effect of an electric current is put to good use.
6. Define Joule’s law.
7. Calculate the amount of heat energy released by a heater which has an element with a resistance of 30 ohms, when a current of 8 amperes flows through it for 20 minutes.
8. An electric kettle draws 9 amperes from the supply for 5 minutes. Te element has a resistance of 25 ohms. Calculate the amount of heat energy released during this time.
(2,304 MJ) (607,5 kJ)
9. The current flow through the element of an electric radiator is 10 amperes. In 3 minutes it generates 432 kJ of heat energy. Determine the resistance of the element.
10. Te element of an electric kettle has a resistance of 50 ohms and draws a current of 4,5 amperes from the supply. How long will it take to generate 250 kJ of heat energy?
(24 Ω) (4,12 minutes)
11. An electric lamp has a filament with a resistance of 450 ohms. Determine the current flow if the heat energy generated in 30 minutes by the lamp, is 170 kJ.
(0,458 2 A)
12. A conductor with a resistance of 0,08 ohms carries a current of 12 amperes for 45 minutes. Determine the amount of heat energy generated by the conductor.
(31,1 kJ)
13. A current of 10 amperes flows through the element of an electric heater for 15 minutes. Te element has a resistance of 20 ohms. Determine the amount of heat energy generated.
14. A stove plate has a resistance of 52 ohms and draws a current of 4,3 amperes from the supply. Determine the time required to generate 565 kJ of heat energy.
15. Determine the time required to generate 375 kJ of heat energy when a current of 2,8 amperes flows through the element of an electrical appliance which has a resistance of 78 ohms.
(1,8 MJ) (9,79 minutes) (10,22 minutes)
16. A current of 5,4 amperes flows through the element of an electric heater for 8 minutes. During this time, 735 kJ of heat energy is generated. Determine the resistance of the element.
(52,51 ohms)
17. An electric heater generates 275 kJ of heat energy in 3 minutes. If the current flow is 6,8 amperes, determine the resistance of the element.
18. A lamp generates 150 kJ of heat energy in 30 minutes. Te filament of the lamp has a resistance of 485 ohms. Determine the current flow.
19. A heater element generates 740 kJ of heat energy in 35 minutes. Determine the current flow if the element has a resistance of 340 ohms.
(33,04 ohms) (0,414 5 A) (1,018 A)
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