For a plane mirror,the focal length is . . . . . . $m$.

$A$ small plane mirror is placed at the center of a spherical screen of radius $R$. Light rays are incident on the mirror. If the mirror is rotated at a frequency of $n$ revolutions per second,what will be the speed of the reflected light spot on the screen?

Light rays fall on a plane mirror and form a real image. Therefore,the incident rays are:

$A$ clock hung on a wall has marks instead of numbers on its dial. On the opposite wall there is a mirror,and the image of the clock in the mirror,if read,indicates the time as $8:20$. What is the actual time in the clock?

The incident ray,reflected ray,and the outward drawn normal are denoted by the unit vectors $\overrightarrow{ a }, \overrightarrow{ b }$ and $\overrightarrow{ c }$ respectively. Choose the correct relation for these vectors.

The light reflected by a plane mirror may form a real image: