A) \[f\text{/2}\,\text{and}\,\text{I/2}\]
B) \[f\,\text{and}\,\text{I/4}\]
C) \[f\text{/2}\,\text{and}\,\text{I/4}\]
D) \[f\,\text{and}\,3\text{I/4}\]
Correct Answer: D
Solution :
Covering the aperture of a lens f will not change but luminous intensity \[I=k(\pi {{r}^{2}})\] Uncovered area \[=\pi {{r}^{2}}-\pi {{\left( \frac{r}{2} \right)}^{2}}=\frac{3}{4}\pi {{r}^{2}}\] So, new intensity \[=\frac{3}{4}k\pi {{r}^{2}}\] \[=\frac{3}{4}I\]You need to login to perform this action.
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