When an object is placed at a distance of 15cm from a concave mirror, its image is formed at 10cm in front of the mirror. Calculate the focal length of the mirror.

A convex lens of power 5D and a concave lens of power 7.5D are placed in contact with each other. What is the:

1. Power of this combination of lenses?
2. Focal length of this combination of lenses?

A 5cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 18cm at a distance of 12cm from it. Use lens formula to determine the position, size and nature to the image formed.

An object is placed at a distance of 12cm in front of a concave mirror of radius of curvature 30cm. List four characteristics of the image formed by the mirror.

State the uses of plane mirrors.

The boy walks towards the mirror at a speed of 1m/ s. At what speed does his image approach him?

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 infinity and device, image formed is diminished and between pole and focus, behind it.

How does the light have to enter the glass:

1. To produce a large amount of bending?
2. For no refraction to happen?

State any four characteristics of the image of an object formed by a plane mirror.

Does the incident and emergent ray coincide in the process of refraction through glass slab? Give reason.