A bulb is located on a wall. Its image is to be obtained on a parallel wall with the help of a convex lens. If the distance between parallel walls is 'd' then the required focal length of the lens placed in between the walls is:
1. | Only \(\frac{\mathrm{d}}{4}\) |
2. | Only \(\frac{\mathrm{d}}{2}\) |
3. | More than \(\frac{\mathrm{d}}{4}\)but less than \(\frac{\mathrm{d}}{2}\) |
4. | Less than or equal to \(\frac{\mathrm{d}}{4}\) |
A biconvex lens is cut into two halves along (i) XOX' and (ii) YOY' as shown in the figure. Let \(f\), \(f'\) \(f''\) be the focal lengths of the complete lens, of each half in case (i), and of each half in case (ii), respectively.
Choose the correct statement from the following:
1. | \(f' = f,f'' =2f\) | 2. | \(f' = 2f, f''=f\) |
3. | \(f' =f, f''=f\) | 4. | \(f'=2f, f''=2f\) |