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InkFlaskCambridge IGCSE

Measure current and voltage · Physics

Ammeter

Ammeter, with labels: scale in A, pointer, zero mark.

What it is for

An ammeter measures electric current, the charge flowing past a point each second, in amperes (A). It is connected in series, so the current through the component also passes through the meter.

Range
0 to 1 A (Practical Test: 1 A or 1.5 A full scale)
Smallest division
0.02 A
Record to
the nearest 0.01 A (half a division), e.g. 0.62 A

Why choose it

For the current through a lamp, resistor or wire, as when you find resistance from R = V ÷ I. A digital ammeter or multimeter shows the number directly, but with either kind pick a range just above the largest current; small currents need a milliammeter (1 A = 1000 mA).

How to read it

00.20.40.60.81Alook straight at the pointer: 0.62 A
  1. Connect it in series: break the loop and put the meter in the gap.
  2. Join its + terminal on the side towards the + of the supply.
  3. Before switching on, check the pointer is on 0.
  4. Count what each division is worth (0.02 A), read the pointer and write the unit: 0.62 A.

Exam-style question

A student connects a battery, a resistor and an ammeter in series, with a voltmeter across the resistor. The ammeter reads 0.62 A and the voltmeter 3.1 V.

  1. Calculate the resistance of the resistor.
  2. The ammeter is moved to the other side of the resistor. What does it read?
  3. What goes wrong if the ammeter is connected in parallel with the resistor?
Show what a good answer says
  1. R = V ÷ I = 3.1 ÷ 0.62 = 5.0 Ω.
  2. Still 0.62 A: the current is the same at every point in a series circuit.
  3. An ammeter has a very small resistance, so most of the current goes through it instead of the resistor; the reading is wrong, and the large current can damage the meter.

Teaching points for checking your own answer, not official Cambridge marks.

Common errors

  • Connecting it in parallel across a component instead of in series: it short-circuits that component.
  • Joining + and − the wrong way round, so the pointer is pushed below 0.
  • Misjudging a division: on this dial each small division is 0.02 A, not 0.01 A or 0.1 A.
  • Choosing a range too small, so the pointer goes off the end, or far too large, so it hardly moves.

Where you use it here

No experiment on the site uses it yet; more are on the way.

From the Practical Test apparatus lists of the Cambridge IGCSE Biology 0610, Chemistry 0620 and Physics 0625 syllabuses for 2026–2028, and the apparatus the experiments on this site use.

More in “Measuring instruments”