Magnification

• We have derived the mirror eqn which determines the image distance in terms of the object distance and the focal length:

• What about the size of the image?
  • How is h’ related to h??
  • From similar triangles:

We can use the mirror eqn to eliminate R from this eqn:

Therefore,

Simplifying,

Now, we can introduce a sign convention. We can indicate that this image is inverted if we define its magnification M as the negative number given by:

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