A) 30 cm towards the mirror
B) 36 cm away from the mirror
C) 30 cm away from the mirror
D) 36 cm towards the mirror
Correct Answer: B
Solution :
[b] |
\[\frac{1}{f}=\frac{1}{{{v}_{1}}}+\frac{1}{u}\] |
\[-\frac{1}{15}=\frac{1}{{{v}_{1}}}-\frac{1}{40}\] |
\[\Rightarrow \frac{1}{{{v}_{1}}}=\frac{1}{-15}+\frac{1}{40}\] |
\[{{v}_{1}}=-24cm\] |
When object is displaced by 20 cm towards mirror. |
Now, |
\[{{u}_{2}}=-20\] |
\[\frac{1}{f}=\frac{1}{{{v}_{2}}}+\frac{1}{{{u}_{2}}}\] |
\[\frac{1}{-15}=\frac{1}{{{v}_{2}}}-\frac{1}{20}\] |
\[\frac{1}{{{v}_{2}}}=\frac{1}{20}-\frac{1}{15}\] |
\[{{v}_{2}}=-60cm\] |
So, image shifts away from mirror by \[=60-24=36cm\]. |
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