An object is placed at a distance of $12\,cm$ in front of a plane mirror. $A$ virtual and erect image is formed by the mirror. Now,the mirror is moved by $4\,cm$ towards the stationary object. The distance by which the position of the image would be shifted is:

$A$ small plane mirror is placed at the centre of a spherical screen of radius $R$. $A$ beam of light is falling on the mirror. If the mirror makes $n$ revolutions per second,the speed of the reflected light spot on the screen will be:

$A$ 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?

$A$ girl of height $150 \,cm$ with her eye level at $140 \,cm$ stands in front of a plane mirror of height $75 \,cm$ fixed to a wall. The lower edge of the mirror is at a height of $85 \,cm$ above her feet level. The height of her image the girl can see in the mirror is (in $cm$)

$A$ cubical room is formed with $6$ plane mirrors. An insect moves along the diagonal of the floor with uniform speed $v_0$. The speed of its image in two adjacent walls,parallel to the walls,is $20\sqrt{2} \ cm/s$. Then the speed of the image formed on the roof with respect to the ground is ...... $cm/s$.

$A$ monochromatic beam of light enters a square enclosure with mirrored interior surfaces at an angle of incidence $\theta_i(\neq 0)$ (see figure). For some value$(s)$ of $\theta_i$,the beam is reflected by every mirrored wall (other than the one with the opening) exactly once and exits the enclosure through the same hole. Which of the following statements about this beam is correct?