Question

Which of the following statements are correct?

1. (a). For a lens the first principal focus is the position of the object whose image is at infinity
2. (b) For a lens the first principal focus is the position of the object whose image is formed at twice the focal length.
3. (c) For a lens the second principal focus is the position of the real image whose object is at infinity
4. (d) For a lens the second principal focus is the position of the object whose image is formed at twice the focal length

• A. i only
• B. i, iii
• C. iii only
• D. None of these

Answer 1

Answer:

B. i, iii

• Options (a) and (c) are correct definitions of the principal focus points for lenses.

• For a lens the first principal focus is the position of the object whose image is at infinity.

• For a lens the second principal focus is the position of the real image whose object is at infinity.