Grade 9 · Science · Unit 9 of 12
Electrical Energy
Power, efficiency and sources
What your child practises
The difference between electricity and electrical energy, energy in joules and kilowatt-hours, cost of electricity, efficiency of devices, and the benefits and challenges of sources such as hydro, wind, solar, nuclear and gas.
Saskatchewan Curriculum outcome: CE9.3, CE9.4 · electrical devices, energy costs and efficiency
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
A remote northern community relies on diesel generators. How can solar panels and battery storage help?
- They reduce diesel use, lowering costs and emissions
- They stop all electricity
- They need more diesel
- They make diesel more expensive
Show answer
They reduce diesel use, lowering costs and emissions
Hint: Many remote communities are adding renewable power to cut fuel use.
Question 2
A device takes in 200 J of electrical energy and gives out 120 J of useful energy. What is its efficiency, as a percent?
answer box%
Show answer
60 %
Hint: Efficiency = useful ÷ input × 100 = 120 ÷ 200 × 100 = 60%.
Question 3
Efficiency is the ratio of…
- total energy to useful energy
- useful energy output to total energy input
- voltage to current
- power to time
Show answer
useful energy output to total energy input
Hint: Efficiency = useful output ÷ total input × 100%.
Question 4
A solar cell changes…
- light energy to electrical energy
- heat to sound
- sound to heat
- electrical energy to light
Show answer
light energy to electrical energy
Hint: A solar cell is a source, not a load.
Question 5
A 3 kW heater runs for 4 hours. How many kilowatt-hours of energy does it use?
answer boxkWh
Show answer
12 kWh
Hint: kWh = kW × hours = 3 × 4 = 12 kWh.
Question 6
Hydroelectric dams provide renewable power. What is one challenge they can cause?
- They burn uranium to heat steam
- They need coal to run
- They can flood land and change river habitats for fish and communities
- They cannot make electricity
Show answer
They can flood land and change river habitats for fish and communities
Hint: Every source has benefits and costs.