What do you understand by the power of a lens? Name one factor on which the power of a lens depends.

A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

Draw ray diagrams showing the image formation by a concave lens when an object is placed:
At the focus of the lens.

Name the lens which always forms a virtual image of an object.

A student focuses the image of a candle flame, placed at about 2 m from a convex lens of focal length 10 cm, on a screen. After that he moves gradually the flame towards the lens and each time focuses its image on the screen.

1. In which direction does he move the lens to focus the flame on the screen?
2. What happens to the size of the image of the flame formed on the screen?
3. What difference is seen in the intensity (brightness) of the image of the flame on the screen?
4. What is seen on the screen when the flame is very close (at about 5 cm) to the lens?

Draw ray diagrams showing the image formation by a convex lens when an object is placed:At twice the focal length of the lens.

How is the reflection of light ray from a plane mirror different from the refraction of light ray as it enters a block of glass?

State the two laws of reflection of light.

Which kind of mirror is used in the headlights of a car? Why is it used for this purpose?

What is the relation between the focal length and radius of curvature of a spherical mirror (concave mirror or convex mirror)? Calculate the focal length of a spherical mirror whose radius of curvature is 25cm.