A student focused the image of a candle flame on a white screen by placing the flame at various distances from a convex lens. He noted his observations as :
| S. No. |
Distance of flame from the lens (cm) |
Distance of the screen from the lens (cm) |
| (i) |
60 |
20 |
| (ii) |
40 |
24 |
| (iii) |
30 |
30 |
| (iv) |
24 |
40 |
| (v) |
15 |
70 |
(a) From the above table, find the focal length of lens without using lens formula.
(b) Which set of observations is incorrect and why ?
(c) In which case, the size of the object and image will be same ? Give reason for your answer.
