In a movie hall,the distance between the projector and the screen is increased by $1\%$. The illumination on the screen is:

Write the names of instruments developed by the use of properties of reflection and refraction of mirrors,lenses,and prisms.

Two plane mirrors of length $L$ are separated by a distance $L$,and a man $M_2$ is standing at a distance $L$ from the connecting line of the mirrors,as shown in the figure. $A$ man $M_1$ is walking in a straight line at a distance $2L$ parallel to the mirrors at a speed $u$. Then,the man $M_2$ at $O$ will be able to see the image of $M_1$ for a total time of:

Column-$I$ contains a list of mirrors and positions of an object. Match this with Column-$II$ describing the nature of the image formed.

For the refraction of light through a prism,which of the following statements is correct?

$A$ lamp is hanging at a height of $40\, cm$ from the center of a table. If its height is increased by $10\, cm$,the illuminance on the table will decrease by what percentage?