How many times is the velocity of light in a vacuum compared to the velocity of light in water?

$A$ girl was playing with a thin beam of light from her laser torch by directing it from different directions on a convex lens held vertically. She was surprised to see that in a particular direction the beam of light continues to move along the same direction after passing through the lens. State the reason for this observation.

What is the distance between the pole and the principal focus of a spherical mirror called?

State the sign convention used to measure distances from a mirror.

$A$ ray of light is incident normally on a reflecting surface. What are the $(i)$ angle of incidence and $(ii)$ angle of reflection?

Which lens can be used as a magnifying glass? For which position of the object does a convex lens form:
$(a)$ a virtual and erect image?
$(b)$ a real and inverted image of the same size as that of the object?
Draw labelled ray diagrams to show the formation of the required image in each of the above two cases.