If a light ray $IM$ is incident on the surface $AB$ of a rectangular glass slab as shown,identify the correct emergent ray.

Zaheen uses a convex lens to make sunlight burn a hole in a piece of card. Zaheen changes the lens in the holder for another lens with twice the power. What will she have to do to focus the sunlight on the card?

$A$ ray of light is incident on a concave mirror after passing through the centre of curvature. What is the angle of incidence (in $°$)?

Draw ray diagrams showing the image formation by a concave mirror when an object is placed:
$(a)$ Between pole $(P)$ and focus $(F)$ of the mirror.
$(b)$ Between focus $(F)$ and centre of curvature $(C)$ of the mirror.
$(c)$ At centre of curvature $(C)$ of the mirror.
$(d)$ $A$ little beyond centre of curvature $(C)$ of the mirror.
$(e)$ At infinity.

$A$ candle is placed at a distance of $10 \ cm$ from a plane mirror. At what distance from the mirror will the image of this candle be formed (in $cm$)?

What is the focal length of the objective of an astronomical telescope as compared to that of the eyepiece?