Quick answer: Electrical power is the rate at which an appliance transfers energy, measured in watts. This grade 8 science test on electrical power has 8 questions worth 20 marks, to do in 40 minutes: meaning of power, cool box and hair dryer. The mark scheme is on a separate page; free printable PDF.
This test has eight questions on power, energy and electricity bills and is worth 20 marks. Write the formula, show each step and give units. You may use a calculator.
Level: Grade 8 science (Year 9 · Class 8) · Curriculum: MS-PS3
Question 1 Meaning of power (2 marks)
- State what is meant by electrical power. (1 mark)
- State the unit of power in full and its symbol. (1 mark)
Question 2 Cool box (2 marks)
A car cool box works on 12 V and draws 3.5 A.- Write the formula for power. (1 mark)
- Calculate the power of the cool box. (1 mark)
Question 3 Hair dryer (3 marks)
A hair dryer has a power of 1.8 kW and is used for 10 minutes.- Calculate the energy transferred in kWh. (2 marks)
- Calculate the energy in joules. (1 mark)
Question 4 Monthly bill (3 marks)
Look at the meter readings of Ifeanyi’s home in Abuja.- Calculate the energy used. (1 mark)
- Calculate the cost. (2 marks)
Question 5 Blender fuse (3 marks)
A blender is rated 1380 W on a 230 V supply. Fuses of 3 A, 5 A and 13 A are available.- Calculate the current. (2 marks)
- Choose the best fuse and give a reason. (1 mark)
Question 6 Why kilowatt-hours? (3 marks)
- Explain why a 2 kW heater costs more to run for one hour than a 100 W television. (2 marks)
- Explain why electricity bills use kilowatt-hours instead of joules. (1 mark)
Question 7 Television or oven (3 marks)
A television of power 120 W is on for 4 hours. An oven of power 2.4 kW is on for 25 minutes.- Calculate the energy used by each in kWh. (2 marks)
- State which uses more energy and by how much. (1 mark)
Question 8 Correct the statement (1 mark)
A student writes: ‘A 2 kW heater uses 2 kWh of energy.’ Correct this statement. (1 mark)
