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.

A convex lens of focal length 25cm and a concave lens of focal length 10cm are placed in close focal contact with each other. Calculate the lens power of this combination.

Show by drawing a ray-diagram that the image of an object formed by a concave lens is virtual, erect and diminished.

A large concave mirror has a radius of curvature of 1.5m. A person stands 10m in front of the mirror. Where is the person’s image?

Explain why, concave mirrors are used as shaving mirrors.

Draw a ray diagram to show the formation of a virtual magnified image of an object by a convex lens. In your diagram, the position of object and image with respect to the principal focus should be shown clearly.

Why does a ray of light passing through the centre of curvature of a concave mirror gets reflected along same path after reflection?

Write down the magnification formula for a lens in terms of object distance and image distance. How does this magnification formula for a lens differ from the corresponding formula for a mirror?