To find the image distance for varying object distances in case of a convex lens of focal length 15 cm, a student obtains on a screen a sharp image of a bright object by placing it at 20 cm distance from the lens. After that he gradually moves the object away from the lens and each time focuses the image on the screen.

1. In which direction-towards or away from the lens does he move the screen to focus the object?
2. How does the size of image change?
3. Approximately at what distance does he obtain the image of magnification -1?
4. How does the intensity of image change as the object moves farther and farther away from the lens?

A student focuses the image of a well illuminated distant object on a screen using a convex lens. After that he gradually moves the object towards the lens and each time focuses its image on the screen by adjusting the lens.

1. In which direction-towards the screen or away from the screen, does he move the lens?
2. What happens to the size of the image-does it decrease or increase?
3. What happens to the image on the screen when he moves the object very close to the lens?

Show the lateral displacement of the ray on the diagram.

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

A boy with a mouth 5cm wide stands 2m away from a plane mirror. Where is his image and how wide is the image of his mouth?

Briefly describe how you would find the focal length of a concave mirror quickly but approximately.

Name the type of mirrors used in the design of solar furnaces. Explain how high temperature is achieved by this device.

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

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?

When a light ray passes from air into glass, what happens to its speed? Draw a diagram to show which way the ray of light bends.