A) Changes from real to virtual when it is at a distance of R from the surface
B) Changes from virtual to real when it is at a distance of R from the surface.
C) Changes from real to virtual when it is at a distance no. of \[\frac{2R}{3}\] from the surface
D) Changes from virtual to real when it is at a distance of \[\frac{2R}{3}\] from the surface
Correct Answer: C
Solution :
[c]Using refraction at spherical surface\[=\frac{2.5}{v}-\frac{1}{u}=\frac{2.5-1}{R}\] |
\[\Rightarrow \] \[\frac{2.5}{v}=\frac{1.5}{R}-\frac{1}{u}\] \[\Rightarrow \] \[v=\frac{2.5uR}{1.5u-R}\] |
\[v=\infty \] at \[1.5u-R=0\Rightarrow u=\frac{2R}{3}\] |
For \[u<\frac{2R}{3},v<0\] virtual image |
\[u>\frac{2R}{3},v>0\] real image |
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