Course: Separate Physics only | Tier: Foundation + Higher | Equation sheet: given in the exam
The equation
magnification = image height ÷ object height
| Quantity | Unit |
|---|---|
| magnification | no unit (it is a ratio) |
| image height | any length unit (same as object) |
| object height | any length unit (same as image) |
Rearranged: image height = magnification × object height | object height = image height ÷ magnification | Both heights must be in the same unit.
Use FIFA for every answer
- F – Formula: write the equation as it appears on the sheet.
- I – Insert: put in the numbers (same unit for both heights).
- F – Fix: rearrange to make the unknown the subject.
- A – Answer: calculate; give a unit for heights (magnification has none).
Foundation: aim for Q1–8. Higher: aim for Q4–10. Most questions need rearranging.
Questions
Q1 (F) A magnifying glass makes a 2 cm insect look 6 cm tall. Calculate the magnification.
Show solution
F: magnification = image height ÷ object height
I: magnification = 6 ÷ 2
F: magnification is already the subject
A: 3 (no unit)
Q2 (F) A ×4 magnifying glass is used to read a letter 5 mm tall. How tall does the letter appear?
Show solution
F: magnification = image height ÷ object height
I: 4 = image ÷ 5
F: image = 4 × 5
A: 20 mm
Q3 (F) A lens gives a magnification of 3. The image of a stamp is 12 cm tall. How tall is the real stamp?
Show solution
F: magnification = image height ÷ object height
I: 3 = 12 ÷ object
F: object = 12 ÷ 3
A: 4 cm
Q4 (F) A 5 mm ant appears 2.0 cm tall through a lens. Calculate the magnification.
Show solution
Convert first: 2.0 cm = 20 mm (same unit as the ant)
F: magnification = image height ÷ object height
I: magnification = 20 ÷ 5
F: magnification is already the subject
A: 4
Q5 (F) A camera forms a 9 mm tall image of a 1.8 m tall person on its sensor. Calculate the magnification.
Show solution
Convert first: 1.8 m = 1800 mm
F: magnification = image height ÷ object height
I: magnification = 9 ÷ 1800
F: magnification is already the subject
A: 0.005 (less than 1: the image is smaller)
Q6 (F/H) A projector has a magnification of 50. The image on the screen is 1.5 m tall. How tall is the picture on the slide, in cm?
Show solution
F: magnification = image height ÷ object height
I: 50 = 1.5 ÷ object
F: object = 1.5 ÷ 50 = 0.03 m
A: 3 cm
Q7 (F/H) A microscope magnifies ×400. The image of a cell is 12 mm across. How big is the real cell?
Show solution
F: magnification = image height ÷ object height
I: 400 = 12 ÷ object
F: object = 12 ÷ 400
A: 0.03 mm
Q8 (F/H) A camera has a magnification of 2.5 × 10−3. The image of a tree on the sensor is 4.5 mm tall. How tall is the tree in metres?
Show solution
F: magnification = image height ÷ object height
I: 2.5 × 10−3 = 4.5 ÷ object
F: object = 4.5 ÷ 2.5 × 10−3 = 1800 mm
A: 1.8 m
Q9 (H) A photo on a phone screen shows a 1.6 m tall friend as 8.0 cm tall. The photo is printed so the image is 5 times bigger than on the phone. Calculate the magnification of the printed photo compared with the real friend.
Show solution
Printed image height: 5 × 8.0 = 40 cm = 0.40 m
F: magnification = image height ÷ object height
I: magnification = 0.40 ÷ 1.6
F: magnification is already the subject
A: 0.25
Q10 (H) A lens gives a magnification of 2.8. The image of a leaf is 15.0 cm tall. Calculate the height of the leaf, to 3 significant figures.
Show solution
F: magnification = image height ÷ object height
I: 2.8 = 15.0 ÷ object
F: object = 15.0 ÷ 2.8 = 5.357… cm
A: 5.36 cm (3 s.f.)
