The focal length of lens will be (refractive index = 1.5)
A) 60 cm
B) 45 cm
C) 120 cm
D) 75 cm
Correct Answer: A
Solution :
The radii of the curvature are positive Thus, \[{{R}_{1}}=+15cm\]and \[{{R}_{2}}=+20cm\] The focal length is given by \[\frac{1}{f}=(\mu -1)\left[ \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right]\] \[\Rightarrow \]\[\frac{1}{f}=(1.5-1)\left[ \frac{1}{15}-\frac{1}{20} \right]\] \[=0.5\times \frac{1}{60}=\frac{5}{600}\]\[\Rightarrow \]\[f=\frac{600}{5}=120cm\]
You need to login to perform this action.
You will be redirected in
3 sec
