Q
Which statements are correct? A: At a lens's first principal focus, an object has its image at infinity. B: At the first focus, its image is at twice the focal length. C: The second principal focus is where an object at infinity forms its image. D: The second focus is an object position giving an image at twice the focal length.
RRB Group-D
18/08/2022 / Shift-I
2022
✓ Answer:
C
Both A and C
A and C describe the first and second principal foci. For a diverging lens the focal image is virtual; the source's description of it as always real is too restrictive.