A) \[\approx \] 3 dioptres
B) \[\approx \] 5 dioptres
C) \[\approx \] 7 diopters
D) \[\approx \] 9 diopters
Correct Answer: B
Solution :
\[f=\frac{{{D}^{2}}-{{x}^{2}}}{4D}\] (Focal length by displacement method) \[\Rightarrow f=\frac{{{(100)}^{2}}-{{(40)}^{2}}}{4\times 40}=21\ cm\] \[\therefore P=\frac{100}{f}=\frac{100}{21}\approx 5\,D\]You need to login to perform this action.
You will be redirected in
3 sec