# CIE IGCSE Biology: 复习笔记：2.1.3 Magnification Formula

### Magnification Formula

#### Calculating magnification and specimen size using millimetres as units

• Magnification is calculated using the following equation:

Magnification = Image size ÷ Actual size

• A better way to remember the equation is using an equation triangle:

Magnification equation

• Rearranging the equation to find things other than the magnification becomes easy when you remember the triangle - whatever you are trying to find, place your finger over it and whatever is left is what you do, so:
• Magnification = image size / actual size
• Actual size = image size / magnification
• Image size = magnification x actual size

Remember magnification does not have any units and is just written as ‘x 10’ or ‘x 5000’

#### Worked Example

An image of an animal cell is 30 mm in size and it has been magnified by a factor of x 3000. What is the actual size of the cell?

To find the actual size of the cell:

Worked example using the magnification equation

#### Exam Tip

This skill most frequently comes up in paper 5 and 6 (although it also comes up in the multiple choice and occasionally the theory paper) and you will definitely have to calculate either magnification, drawing size or actual size in a least one paper.To ensure you do not lose marks:

1. Always look at the units that have been given in the question - if you are asked to measure something, most often you will be expected to measure it in millimetres NOT in centimetres - double check the question to see!
2. Learn the equation triangle for magnification and write it on the page straight away
3. Don’t forget that magnification has NO UNITS - students often lose a mark because they put one in