Magnification Formula (Cambridge International IGCSE Science)

Magnification Formula

• Magnification can calculated using the following formula:

magnification = image size ÷ actual size

• This formula can be entered into an equation triangle to aid memory and allow for easy rearranging:

• The triangle allows the formula to be rearranged as follows:

  • Magnification = image size ÷ actual size
  • Actual size = image size ÷ magnification
  • Image size = magnification x actual size

• When using the magnification formula it is essential that any units used in the calculation are the same, e.g. if the size of an image is measured in mm then the actual size of the object must also be in mm within the calculation

• Note that magnification does not have any units and is just written as, e.g. x10 or 5000x

Worked Example An image of an animal cell measures 30 mm with a ruler and has been magnified by a factor of x3000.

What is the actual size of the cell?

Exam Hint This skill most often comes up in papers 5 and 6, though it sometimes appears in multiple choice and the theory paper.

Remember the following when carrying out magnification calculations:

1. Always look at the units that have been given in the question - you will usually be expected to measure objects in mm rather than in cm - double check the question to see!
2. Learn the equation triangle for magnification
3. Don’t forget that magnification has no units - students often lose a mark because they put one in