The angle made by the incident ray of light with the reflecting surface is called:

$A$ flat mirror $M$ is arranged parallel to a wall $W$ at a distance $l$ from it. The light produced by a point source $S$ kept on the wall is reflected by the mirror and produces a light spot on the wall. The mirror moves with velocity $v$ towards the wall.

Two plane mirrors are inclined at $70^{\circ}$. $A$ ray incident on one mirror at an angle $\theta$ with the surface,after reflection,falls on the second mirror and is reflected from there parallel to the first mirror. The value of $\theta$ is ......$^{\circ}$.

$A$ point source of light $S$ at a distance $d$ from the screen $A$ produces light intensity $I_0$ at the centre of the screen. If a completely reflecting mirror $M$ is placed at a distance $d$ behind the source as shown in the figure,treating the object and its image as incoherent with each other,find the intensity at the centre of the screen.

$A$ light bulb is placed between two plane mirrors inclined at an angle of $60^{\circ}$. The number of images formed is:

When an object is placed between two parallel mirrors,the number of images formed is: