Ray $1$ is parallel to the horizontal mirror. Ray $2$ is parallel to the other mirror. Then the angle between the two mirrors is .......... $^o$.

Two plane mirrors $M_1$ and $M_2$ have a length of $20 \, m$ each and are $10 \, cm$ apart. $A$ ray of light is incident on one end of mirror $M_2$ at an angle of $53^{\circ}$. The number of reflections the light undergoes before reaching the other end is

$A$ 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.

Two mirrors,labeled $LM$ for left mirror and $RM$ for right mirror in the adjacent figure,are parallel to each other and $3.0 \, m$ apart. $A$ person standing $1.0 \, m$ from the right mirror $(RM)$ looks into this mirror and sees a series of images. How far from the person is the second closest image seen in the right mirror $(RM)$ (in $, m$)?

Images formed by an object placed between two plane mirrors whose reflecting surfaces make an angle of $90^o$ with one another lie on

$A$ thick plane mirror shows a number of images of the filament of an electric bulb. Of these,the brightest image is the