KinexiaLEARN PHYSICS

Lens Magnification — Microscope Objective (Worked Example)

Easy
Problem

A microscope objective forms an image 30 cm from the lens of an object placed 2.0 cm away. What is the linear magnification?

Given

  • do = 2.0 cm

  • di = 30 cm

Find

The magnification m.

Principle

m = −di/do: the negative sign marks a real, inverted image; |m| > 1 means enlarged.

Formula

Solution

  1. Write the formula: m=−di/dom = -d_i/d_o

  2. Substitute: m=−30/2.0m = -30/2.0

  3. Divide: m=−15m = -15

−15 (15× enlarged, inverted)

Unit check

cm ÷ cm — dimensionless, as magnification must be.

What this means physically

−15: the image is 15 times larger and inverted. Compound microscopes multiply this by the eyepiece (e.g. 10×) for 150× total.

Common mistake

Dropping the minus sign. The sign carries meaning: negative = real and inverted, positive = virtual and upright.