Q28 of 284 Page 240

How could you find the focal length of a convex lens rapidly but approximately?

Change the distance of the screen from the convex lens until a clear inverted image of the window is formed on the screen. Measure the distance of the screen from the lens with a scale. This distance will be the focal length of convex lens.


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26

Where the object must be placed for the image formed by a converging lens to be:

(a) Real, inverted and smaller than the object?


(b) Real, inverted and same size as the object?


(c) Real, inverted and larger than the object?


(D) Virtual, upright and larger than the object?

 27

Draw a diagram to show how a converging lens held close to the eye acts as a magnifying glass. Why is it usual to choose a lens of short focal length for this purpose rather than one of long focal length?

 29

With the help of a labeled diagram explain how a convex lens converges a beam of parallel light rays.

 29

State whether convex lens has a real focus or a virtual focus.