A converging lens and a diverging lens of equal focal lengths are placed coaxially in contact. The focal length and power of this combination will be

Focal length ($F_C$) = ∞; power of combination ($P_C$) = 0

The correct answer is Option (2) → Focal length ($F_C$) = ∞; power of combination ($P_C$) = 0

Given:

Converging lens → focal length $f_1 = +f$

Diverging lens → focal length $f_2 = -f$

When two lenses are placed in contact, the equivalent focal length is:

$\frac{1}{F_C} = \frac{1}{f_1} + \frac{1}{f_2}$

Substitute values:

$\frac{1}{F_C} = \frac{1}{f} + \frac{1}{-f} = 0$

⇒ $F_C = ∞$

Power of combination:

$P_C = \frac{1}{F_C} = 0$

Final Answer:

Focal length $(F_C) = ∞$ ; Power of combination $(P_C) = 0$