A) 12 cm
B) 30 cm
C) 50 cm
D) 60 cm
Correct Answer: C
Solution :
The lens formula is \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] |
we have |
\[u=-30\,cm,\,\,f=20\,cm\] |
\[\therefore \] \[\frac{1}{20}=\frac{1}{v}-\frac{1}{-30}\] |
or \[\frac{1}{v}=\frac{1}{20}-\frac{1}{30}=\frac{3-2}{60}=\frac{1}{60}\] |
\[\therefore \] \[v=60\,cm\] |
The ray diagram for the problem is shown as follows: |
For the image (I) coincident with object (O) the rays after refraction from the lens must fail on the convex mirror normally or the rays refracted from lens must meet at C. |
\[\therefore \] \[LC=v=60\text{ }cm\] |
Thus, distance between lens and mirror |
\[LM=60-10=50\text{ }cm\] |
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