Question

Two thin lenses of powers 2D and 3D are placed in contact. An object is placed at a distance of 30 cm from the combination. The distance (in cm) of the image from the combination is :

• A. 30
• B. 40
• C. 50
• D. 60

Answer 1

Answer: (D)

60

Power, $P=P_1+P_2$

$P=(2+3)D$

$=5D$

$f=\frac{100}{P}$

$=20cm$

By lens formula, $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

$\frac{1}{v}-\frac{1}{-30}=\frac{1}{20}$

$\frac{1}{v}=\frac{1}{60}$

$v$=60 cm