Two lenses of power 3D and -1D are kept in contact. The focal length of the combined lens would be:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 50 cm
Power of the combined lens (P) is,
$P=P_1+P_2$
$=3D+(-1D)=2D$
and,
focal length (f) is,
$f=\frac{1}{P(m)}=\frac{100}{2}=50cm$