Current, voltage, series and parallel
Two measurements explain almost every circuit you will build: current in amperes and potential difference in volts. This lesson gets the difference straight and then compares series with parallel.
Part of your national curriculum
- Physics: electricity and magnetism: Understand electric current, measured in amperes, in circuits, series and parallel circuits, and potential difference measured in volts
Lesson overview
What you'll learn in this lesson
Understand electric current, measured in amperes, in circuits, series and parallel circuits, and potential difference measured in volts
Key learning points
- • Current: the flow
- • Potential difference: the push
- • Series circuits
- • Parallel circuits
This lesson at a glance
- 30 minutes
- 19 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 19
Watch first
Current, voltage, series and parallel
Learn what voltage, current and resistance actually mean in a circuit.
Do it for real
The practicals below use what the film shows, with a full method you can follow at home.
In a nutshell
Understand electric current, measured in amperes, in circuits, series and parallel circuits, and potential difference measured in volts
What you already know
Part 2 of 19
Before we start
What you already know
You should know that a circuit needs a complete loop and a cell to make a lamp light.
Key words
Part 3 of 19
Key words
Words you'll need today
- Current
- The rate of flow of charge, measured in amperes (A) with an ammeter in series.
- Potential difference
- The energy transferred per unit charge, measured in volts (V) with a voltmeter across a component.
- Series
- Components connected in a single loop.
- Parallel
- Components on separate branches of the circuit.
- Resistance
- How much a component opposes current, measured in ohms.
Learning cycle
Part 4 of 19
Learning cycle 1 of 2
Current and potential difference
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 5 of 19
Learn
Current: the flow
Current is charge flowing, measured in amperes with an ammeter connected in series - in the loop, so the current passes through it. Charge is not used up on the way round: the current entering a lamp equals the current leaving it. In a single loop the current is the same everywhere, no matter where you break in to measure it.
Explore the idea
Part 6 of 19
Learn
Potential difference: the push
Potential difference, measured in volts, is the energy transferred per unit of charge. A voltmeter goes across a component, in parallel with it, because you are comparing two points. The cell provides the push; each component takes a share of it. Current flows through a component; potential difference is across it - that phrasing is worth memorising.
Quick check
Part 7 of 19
Quick check
Current is measured in...
Quick check
Part 8 of 19
Quick check
A voltmeter should be connected...
Reset break
Part 9 of 19
Pause
That's sitting 1 of 2 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 10 of 19
Learning cycle 2 of 2
Series against parallel
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 11 of 19
Learn
Series circuits
One loop, one path. Current is identical everywhere, and the cell's potential difference is shared between the components - two identical lamps on a 6 V cell get 3 V each and glow dimly. Add more lamps and total resistance rises, so current falls and all of them dim. Break the loop anywhere and everything goes out, which is why series is a poor choice for house lighting.
Explore the idea
Part 12 of 19
Learn
Parallel circuits
Separate branches. Each branch gets the full cell potential difference, so lamps stay at normal brightness and each can be switched independently; if one fails, the others carry on. The current from the cell splits between branches and rejoins, so total current is the sum of the branch currents - and the cell drains faster. Home wiring and car headlights are parallel for exactly these reasons.
Quick check
Part 13 of 19
Quick check
In a series circuit with two identical lamps and a 6 V cell, each lamp gets...
Quick check
Part 14 of 19
Quick check
In a parallel circuit, if one lamp fails the others...
Common mix-ups
Part 15 of 19
Common mix-ups
Things people often get wrong
- Current is not used up going round a circuit.
- Ammeters go in series; voltmeters go across a component.
- Current flows through; potential difference is across.
- In parallel each branch gets the full cell voltage, not a share.
Challenge round
Part 16 of 19
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
Challenge round
Part 17 of 19
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
____ is charge flowing, measured in amperes with an ammeter connected in series - in the loop, so the current passes through it.
Potential difference, ____ in volts, is the energy transferred per unit of charge.
Mastery quiz
Part 18 of 19
Marked quiz
End of lesson quiz: Current, voltage, series and parallel
6 questions, marked with the reasoning shown. No timer.
1. In a single-loop series circuit, current is...
2. Adding a third lamp in series makes the lamps...
3. Total current from the cell in a parallel circuit is...
4. Potential difference is measured in...
5. House lighting is wired in parallel so that...
6. Which phrase is correct?
Lesson round-up
Part 19 of 19
Lesson round-up
Ready when you are
Quiz score
Not sat
Games
Not played
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 LunaDo the work
Your written work for this lesson
This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.
Why the school greenhouse failed
A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.
The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.
The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.
Written for Good Learning Co.
Reading questions
- Name the variable the club changed the second time, and one variable they kept the same.
- Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
- Write a conclusion for the club's report, saying how far the evidence supports it.
Method and results
WritingWrite the aim, what you changed, what you measured and what you kept the same, then record your results in a table.
1 page + results table
Conclusion
WritingExplain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.
6–8 sentences
Labelled diagram
DiagramDraw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
ReadingRead the lesson text again and write the key ideas in your own words.
Half a page of notes
Saved as you type.
Part 1 of 19 · Watch & discover
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Understand electric current, measured in amperes, in circuits, series and parallel circuits, and potential difference measured in volts