Concave Mirror Rays - Optics Step by Step

A concave mirror can form a real image where checked reflected rays meet in front of the mirror.

optics The image point is accepted only when independent reflected-ray geometry agrees with the mirror equation.

Example

A concave mirror can form a real image where checked reflected rays meet in front of the mirror. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

A concave mirror has a front focus

Use a concave mirror with focal length 6 metres. Put the object 12 metres in front of the mirror, outside the focus.

f = 6\ \text{m}\qquad u = 12\ \text{m}

Reflected rays agree on the image

The vertex ray and the parallel-to-focus ray meet at the same front-side point. That agreement is the real mirror image.

\text{reflected ray intersection} = \text{image point}

Object distance changes the meeting point

Hold the concave focal length fixed. Moving the object changes where the reflected rays meet and changes the inverted scale.

\begin{array}{c|c|c|c}f&u&v&m\\6\ \text{m}&18\ \text{m}&9\ \text{m}&\tfrac{-1}{2}\\6\ \text{m}&12\ \text{m}&12\ \text{m}&-1\\6\ \text{m}&9\ \text{m}&18\ \text{m}&-2\\\end{array}