Two plane mirrors are parallel to each other and an object $O$ is placed between them. Then the distance of the first three images from the mirror $M_2$ will be (in $cm$):

$A$ beam of light from a source $L$ is incident normally on a plane mirror fixed at a certain distance $x$ from the source. The beam is reflected back as a spot on a scale placed just above the source $L$. When the mirror is rotated through a small angle $\theta$,the spot of the light is found to move through a distance $y$ on the scale. The angle $\theta$ is given by

$A$ point source of light $S$ is placed at a distance $10\,cm$ in front of the centre of a mirror of width $20\,cm$ suspended vertically on a wall. $A$ man walks with a speed $10\,cm/s$ in front of the mirror along a line parallel to the mirror at a distance $20\,cm$ from it as shown in the figure. Find the maximum time during which he can see the image of the source $S$ in the mirror. (in $,s$)

Power of a plane mirror is . . . . . .

$A$ ray reflected successively from two plane mirrors inclined at a certain angle undergoes a deviation of $270^o$ after two reflections. The number of images observable is:

To get three images of a single object, the angle between the two plane mirrors should be (in $^{\circ}$)