IGCSE Physics (0625)

Reading a linear scale (ruler, cylinder, thermometer)

What this topic tests, the mistakes that cost marks, and one exam-style question worked through step by step.

Key ideas and common mistakes

Reading a thermometer with evenly spaced marks requires estimating values between labeled intervals.
Common mistake: Students often misread halfway points as the nearest labeled value instead of interpolating, e.g., halfway between 30 and 40 is 35, not 30 or 40.
To read the volume in a measuring cylinder, use the value at the bottom of the meniscus, not the top or the nearest marked line above or below.
Reading a scale requires stating the value exactly as shown at the pointer's position, including correct units and decimal places, rather than rounding or omitting detail (e.g., writing 8 instead of 8.4 or missing 'cm').
The correct table heading uses the format 'quantity / unit' (e.g., temperature / degrees Celsius), and the value entered is the thermometer reading as a bare number, not repeated with the unit.
Common mistake: Students often wrongly include the unit in the value or use the wrong heading format.
To read a metre rule, count the 1 mm divisions past the last centimetre mark, then write the length in cm with one decimal place, because each division is 0.1 cm.
To read a thermometer with evenly spaced divisions, add the number of small divisions above the last labeled value, multiplying by the value per division, and always include the correct unit.
Common mistake: Students often miscount divisions or omit the unit.

State the volume of water shown in the measuring cylinder.

Try it first, then show the working

35 cm³

The bottom of the meniscus sits on the 35 mark, so the volume is 35 cm³ read at eye level.

Answer: 35 cm³

23 exam-style questions on Reading a linear scale (ruler, cylinder, thermometer), each marked to the scheme.