Grade 9 · Science · Unit 9 of 11
Circuits & Ohm's Law
Current, voltage and resistance
What your child practises
Circuit components and their jobs, current, potential difference and resistance with their symbols and SI units, calculating with V = I × R, and how current, voltage and resistance behave in series and parallel circuits.
Ontario Curriculum expectation: D2.3, D2.4, D2.5, D2.6 · DC circuit parts, electrical quantities and units, Ohm's law, and series and parallel circuits
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 thicker wire of the same material and length has…
- less resistance
- the same resistance
- infinite resistance
- more resistance
Show answer
less resistance
Hint: A wider wire gives charge more room to flow.
Question 2
Two bulbs are in series. The current through the first is 2 A. What is the current through the second, in amperes?
answer boxA
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2 A
Hint: In a series circuit there is only one path, so the current is the same everywhere.
Question 3
In a parallel circuit, if one bulb burns out, the others…
- get dimmer for good
- stay lit
- go out too
- explode
Show answer
stay lit
Hint: Each branch is its own path to the battery.
Question 4
A 20 V battery is connected across a 5 Ω resistor. What is the current, in amperes?
answer boxA
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4 A
Hint: I = V ÷ R = 20 ÷ 5 = 4 A.
Question 5
Two bulbs are connected in parallel across a 9 V battery. What is the potential difference across each bulb, in volts?
answer boxV
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9 V
Hint: Each branch of a parallel circuit has the same potential difference as the source.
Question 6
A circuit has a current of 2 A through a resistance of 6 Ω. What is the potential difference across it, in volts?
answer boxV
Show answer
12 V
Hint: V = I × R = 2 × 6 = 12 V.