Virtual image on screen As plane mirrors always form virtual images and virtual images can not be obtained on a screen then how can we obtain the image of sun on wall or anything (screen) by plane mirror as on  sunny day. Usually children here in India do mischief while focussing that light on other people's eyes. 
 A: Reflecting sunlight with a mirror doesn't create an image. It creates a area which appears brighter than the surrounding area. This is because more photons are striking that area than the surrounding area. The same happens if you reflect the light into someone's eyes. 
A: A small mirror that reflects the sunlight creates a patch on the wall that is the same size as the mirror, but convolved with the (angular) size of the sun.
This is, in some sense, like a "pinhole camera" - except that the light is being reflected rather than transmitted by the "pinhole" (the small mirror).
If the mirror is small, and the distance to the screen/wall is large, you will in fact create an image of the sun - you can confirm this by seeing that if a cloud moves in front of the sun, you will see the image of the cloud.
I tried to illustrate that below. On the left is the situation of a "small mirror" generating an image of the sun; on the right, a "small sun, large mirror" situation where the image is essentially the image of the mirror. Of course any real situation is somewhere between these two.

