Circuits, resistance and electrical power
Circuit questions reduce to three quantities — current, potential difference and resistance — and the rules that connect them in series and parallel.
Lesson overview
What you'll learn in this lesson
Calculate energy transfers and analyse electrical circuits at GCSE standard.
Key learning points
- • The core relationships
- • Series and parallel
- • Components and safety
This lesson at a glance
- 30 minutes
- 20 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 20
Visual introductionPicture this
Circuits, resistance and electrical power
Circuit questions reduce to three quantities — current, potential difference and resistance — and the rules that connect them in series and parallel.
In a nutshell
Calculate energy transfers and analyse electrical circuits at GCSE standard.
Learning cycle
Part 2 of 20
Learning cycle 1 of 2
Part 1 · The core relationships
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 20
Learn
The core relationships
Current is the rate of flow of charge, Q = It, and potential difference is the energy transferred per unit charge. Ohm's law, V = IR, holds for an ohmic conductor at constant temperature; a filament lamp's resistance rises as it heats, so its graph curves.
Reset break
Part 4 of 20
Pause
That's sitting 1 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 20
Learn
Series and parallel
In series the current is the same everywhere and potential differences add, so total resistance is the sum. In parallel each branch has the full potential difference and currents add, so adding branches reduces total resistance. This is why household circuits are wired in parallel.
Quick check
Part 6 of 20
Quick check
Part 7 of 20
Reset break
Part 8 of 20
Pause
That's sitting 2 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 20
Learning cycle 2 of 2
Part 2 · Components and safety
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 20
Learn
Components and safety
A thermistor's resistance falls as temperature rises, and a light-dependent resistor's falls as light increases, making both useful in sensing circuits. Mains electricity is alternating at 230 V and 50 Hz; the earth wire and fuse or circuit breaker together prevent a fault from making a metal case live.
Quick check
Part 11 of 20
Reset break
Part 12 of 20
Pause
That's sitting 3 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 13 of 20
Explore the idea
Part 14 of 20
Worked example
Worked answer: a 12 V supply drives 0.4 A through a resistor. Find the resistance and the power (4 marks)
Rearranging V = IR gives R = V ÷ I (1). R = 12 ÷ 0.4 = 30 Ω (1). Power P = IV (1), so P = 0.4 × 12 = 4.8 W (1). Checking with P = I²R gives 0.4² × 30 = 4.8 W, confirming the answer, which is a quick way to catch a slip in either calculation.
Challenge round
Part 15 of 20
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Reset break
Part 16 of 20
Pause
That's sitting 4 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 17 of 20
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Current is the rate of flow of charge, Q = It, and potential difference is the ____ transferred per unit charge.
This is why household ____ are wired in parallel.
Challenge round
Part 18 of 20
Game · Recall cards
Ohm's law states
Card 1 of 4
Mastery quiz
Part 19 of 20
Marked quiz
End of lesson quiz: Circuits, resistance and electrical power
4 questions, marked with the reasoning shown. No timer.
1. Ohm's law states
2. In a series circuit the current is
3. Adding a parallel branch makes total resistance
4. A thermistor's resistance
Lesson round-up
Part 20 of 20
Lesson round-up
Ready when you are
Quiz score
Not sat
Games
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Points this lesson
0
Best run
0 in a row
Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 20 · Watch & discover