The optician’s prescription for a spectacle lens is marked +0.5D. What is the:

1. Nature of spectacle lens?
2. Focal length of spectacle lens?

Draw a ray diagram to show the path of the reflected ray corresponding to an incident ray which is directed towards the principal focus of a convex. mirror. Mark on it the angle of incidence and the angle of reflection.

Identify the device used as a spherical mirror or lens in following cases, when the image formed is virtual and erect in each case.Object is placed between the focus and device, image formed is enlarged and on the same side as that of the object.

List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining image of a distant object on a screen.

The refractive indices of glass and water with respect to air are 3/2 and 4/3 respectively. If speed of light in glass is 2×108 m/s, find the speed of light in water.

An object is placed at a distance of 15 cm from a concave lens of focal length 30 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.

Draw and complete the following diagrams to show what happens to the beams of light as they enter the glass block and then leave it:

A concave mirror and a convex lens are held separately in water. What changes, if any, do you expect in the focal length of either?

A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it. Where is the image located?

What is meant by power of a lens? What does its sign (+ve or -ve) indicate? State its S.I. unit. How is this unit related to focal length of a lens?