Grade 10 · Physical Sciences
Electric circuits
Calculate current and potential difference, and compare simple series and parallel circuits.
Current and potential difference
Current is charge passing a point per second. Potential difference is energy transferred per unit charge. Connect an ammeter in series and a voltmeter in parallel with the component.
Series and parallel
In a series circuit the current is the same through each component. In parallel branches the potential difference is the same; branch currents add to the total current.
Formula sheet
- I = Q / Δt
- V = W / Q
- Series resistance: Rtotal = R₁ + R₂ + …
Worked example
A charge of 24 C passes a point in 8 s. Find the current.
- Use I = Q / Δt.
- Substitute Q = 24 C and Δt = 8 s.
- I = 24 / 8 = 3 A.
Try it yourself
1. A cell transfers 18 J to 6 C of charge. Find its potential difference. Check answer
V = W / Q = 18 / 6 = 3 V.
2. Two series resistors are 2 Ω and 5 Ω. Find their combined resistance. Check answer
Rtotal = 2 + 5 = 7 Ω.
Common mistake: A voltmeter belongs in parallel. Do not connect it as though it were an ammeter.