IGCSE · Practice questions · Magnification and size of specimens

Three quantities, one triangle.

Six original Cambridge-style questions on magnification: calculating magnification, actual size and image size from drawings and photographs, with Extended unit conversions between millimetres and micrometres.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Same units, then divide.

M = I ÷ A; rearranged, A = I ÷ M and I = M × A.
Measure the image in mm: 1 cm = 10 mm.
Extended: 1 mm = 1000 μm; convert both sizes to the same unit before dividing.
Magnification has no unit: write ×600, and check the actual size is smaller than the image.

Recall

[1 marks]

State the formula that links magnification, image size and actual size.

magnification = image size ÷ actual size. ✓

Calculation

[2 marks]

A drawing of a cheek cell is 45 mm wide. The actual width of the cell is 0.06 mm. Calculate the magnification of the drawing.

magnification = image size ÷ actual size = 45 ÷ 0.06. ✓
= ×750. ✓

Calculation

[2 marks]

A photograph of an ant is magnified ×12. The image of the ant is 48 mm long. Calculate the actual length of the ant in mm.

actual size = image size ÷ magnification = 48 ÷ 12. ✓
= 4 mm. ✓

Data

[3 marks]

A student draws a leaf cell. She measures the drawing between two marked points as 7.2 cm. The magnification of the drawing is ×1200. Calculate the actual length of the cell in mm.

Convert the image to mm: 7.2 cm = 72 mm. ✓
actual size = 72 ÷ 1200. ✓
= 0.06 mm. ✓

Calculation

[3 marks]

Extended. A bacterium is 2 μm long. An image of it in a textbook is 30 mm long. Calculate the magnification of the image.

Convert to the same unit: 2 μm = 2 ÷ 1000 = 0.002 mm. ✓
magnification = 30 ÷ 0.002. ✓
= ×15 000. ✓

Analysis

[3 marks]

Extended. A photomicrograph of an Amoeba is printed at ×150. The image is 67.5 mm long. Calculate the actual length of the Amoeba, giving your answer in μm.

actual size = 67.5 ÷ 150 = 0.45 mm. ✓
Convert to μm: 0.45 × 1000. ✓
= 450 μm. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.