Mirror Equation Calculator

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Understanding the Mirror Equation

The mirror equation relates the focal length of a spherical mirror to the distances of the object and the image from the mirror.

1/f = 1/do + 1/di
  • f: Focal length of the mirror.
  • do: Distance of the object from the mirror.
  • di: Distance of the image from the mirror.

Sign Convention:

  • Concave Mirror: f is positive.
  • Convex Mirror: f is negative.
  • Real Image: di is positive.
  • Virtual Image: di is negative.

Frequently Asked Questions

What happens if do = f?

If the object is placed at the focal point, the image is formed at infinity (reflected rays are parallel).

Can di be negative?

Yes, a negative image distance indicates a virtual image formed behind the mirror.

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