Place ammeters and voltmeters in circuit diagrams
Translate measurement intentions into series and parallel connections and recognize dangerous meter bypasses in a diagram.
Section 4.3.1 · Circuit diagrams and circuit components
Core and Extended; Physics 0625, 2026–2028. Use the stated source, operating conditions and meter ranges. Written practice is self-checked.
Before you begin
- Read current and p.d. units.
- Trace a component path and its two endpoints.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does an ammeter measure?
What you will learn
- Draw A and V meter symbols.
- Place each meter according to the quantity it measures.
Match the meter to its connection
An ammeter is represented by a circle containing A. Insert it in series in the path whose current is required so that current passes through the meter. Its low resistance minimizes its effect in the ideal model. It is not connected directly across an ideal voltage source, which would provide a low-resistance bypass.
A voltmeter is a circle containing V. Connect it across the two points whose potential difference is required. Its high resistance means negligible extra branch current in the ideal model. A voltmeter across the source reads a different pair of terminals from one across a single component in a series arrangement.
Trace what is actually measured
In a branched circuit, a source-path ammeter measures total current, while an ammeter in one branch measures that branch current. If a real voltmeter draws appreciable current, an ammeter before the split includes its current too. State negligible loading when equating the upstream reading with only the resistor current.
Written diagrams use isolated low-voltage sources, suitable meter ranges and teacher-checked connections before energising. Draw A and V visibly and show each lead endpoint. The physical placement of a meter near a resistor does not prove its correct connection. These exercises do not certify safe practical instrument use.
Pause and explain
A meter marked A is connected directly across an ideal source. What is wrong?
Worked example
Show meters to determine a resistor current and the p.d. across it.
Show the worked solution
- Place an A circle in the resistor path.
- Connect a V circle between the two resistor endpoints.
- Under negligible voltmeter loading, the A reading represents resistor current.
Answer A in series; V across the resistor; negligible voltmeter loading stated.
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Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Draw an ammeter measuring current through a resistor in a cell circuit.
Give me a hint
Interrupt the load path and insert the current meter there.
Compare my reasoning
- Draw a complete cell–resistor loop.
- Insert a circle containing A in series.
- Check that the resistor path passes through the ammeter.
A-labelled meter in the resistor series path.
Look for these in your work
- Use A clearly.
- Avoid a source bypass.
Add a voltmeter measuring the resistor p.d. and explain both lead connections.
Give me a hint
Identify the two ends of the resistor first.
Compare my reasoning
- Draw a circle containing V as a separate measurement branch.
- Connect one lead to each resistor endpoint.
- Explain that it compares the potentials of exactly those two points.
V-labelled meter across the resistor endpoints.
Look for these in your work
- Connect both endpoints.
- Do not put V in the sole series path.
A real voltmeter draws current across a resistor, and an ammeter is upstream of their split. Does the A reading equal resistor current exactly?
Give me a hint
Trace both currents after the split.
Compare my reasoning
- The ammeter carries current into both branches.
- Its reading includes resistor and voltmeter current.
- Equality is only an approximation when voltmeter current is negligible.
No; the upstream reading includes voltmeter current unless its loading is negligible.
Look for these in your work
- Trace the branch split.
- State the idealization for the approximation.
Common mistakes
- A across a source is a low-resistance bypass.
- V must connect to the intended endpoint pair.
- An upstream ammeter may include voltmeter current.
What can you explain now?
Where does a voltmeter connect to measure a component p.d.?
Compare with the explanation
Across its two endpoints.
P.d. is a difference between two points, so the meter requires those two connections.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Draw A in the relevant current path and V across the intended two points, with loading assumptions stated.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.