Linear Magnification (Cambridge (CIE) O Level Physics): Revision Note

Linear Magnification

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

$\mathrm{magnification}=\frac{\mathrm{image}\mathrm{height}}{\mathrm{object}\mathrm{height}}$

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

Magnification Formula Triangle

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 is diminished