Linear Magnification (Cambridge O Level Physics)

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Linear Magnification

  • The magnification of a lens is equal to the ratios of the image height and the object height

magnification space equals space fraction numerator image space height over denominator object space height end fraction

  • This equation can be rearranged with the help of a formula triangle:

Magnification Formula Triangle

Magnification Triangle, downloadable IGCSE & GCSE Physics revision notes

Magnification, image height and object height formula triangle

  • The magnification depends on:
    • The distance of an object from the lens
    • The power of the lens

  • The units for height are unimportant, provided that both the object and image are measured in the same units
    • For example, both in cm, or both in mm

  • Therefore, magnification does not have units as it is a ratio
  • If the magnification is:
    • > 1, then the image is magnified
    • = 1, then the object and image are the same size
    • < 1, then the image isĀ diminished

Worked example

A person sees an image from a magnifying glass.Magnification Worked Example Questions, downloadable IGCSE & GCSE Physics revision notes Calculate the magnification of this image. Clearly show your working on the diagram.

Answer:

Step 1: Measure the height of the object and image from the scale

Magnification Worked Example Solution, downloadable IGCSE & GCSE Physics revision notes

  • The object is 10 cm
  • The image is 20 cm

Step 2: Substitute values into the magnification equation

magnification space equals space 20 over 10 space equals space 2

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Dan MG

Author: Dan MG

Expertise: Physics

Dan graduated with a First-class Masters degree in Physics at Durham University, specialising in cell membrane biophysics. After being awarded an Institute of Physics Teacher Training Scholarship, Dan taught physics in secondary schools in the North of England before moving to SME. Here, he carries on his passion for writing enjoyable physics questions and helping young people to love physics.