Size of specimens — Cambridge IGCSE Combined Science
Use magnification = image size ÷ actual size to find magnification and real size, and convert between mm and µm.
Revision notes
1 short note, in the order of the specification. Each one in short:
Magnification and actual size
PracticalMagnification is how many times larger an image is than the actual size of the specimen: magnification = image size ÷ actual size. Measure the image in millimetres and use the same unit for both sizes. Magnification has no units. There are 1000 micrometres in 1 millimetre, so multiply millimetres by 1000 to get micrometres.
Exam questions
5 exam-style questions (11 marks), each with its mark scheme.
Answer the questionsFlashcards
5 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of organisation of the organism on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
State the magnification formula.
Show answer
Magnification = image size ÷ actual size.
A cell has an image size of 30 mm and an actual size of 0.1 mm. What is the magnification?
Show answer
× 300.
Supplement How many micrometres are in 1 millimetre?
Show answer
1000 µm.
Supplement Convert 0.5 mm to µm.
Show answer
500 µm.
Written and checked against the Cambridge IGCSE Combined Science (0653) specification · Updated October 2026