[JEE Main Online Paper Held On 12-Jan-2019 Morning]
A) 70 cm from point B at right; real
B) \[\frac{20}{3}cm\]from point B at right, real
C) 40 cm from point B at right, real
D) 70 cm from point B at left, virtual
Correct Answer: A
Solution :
For the first lens, \[\frac{1}{{{v}_{1}}}-\frac{1}{{{u}_{1}}}=\frac{1}{{{f}_{1}}}\] \[\Rightarrow \]\[\frac{1}{{{v}_{1}}}+\frac{1}{20}=\frac{1}{5}\Rightarrow {{v}_{1}}=\frac{20}{3}=6.67cm\] Now, for the second lens, \[{{u}_{2}}=6.67-2=\frac{14}{3}cm\] \[\frac{1}{{{v}_{2}}}-\frac{1}{{{u}_{2}}}=\frac{1}{{{f}_{2}}}\Rightarrow \frac{1}{{{v}_{2}}}=\frac{1}{-5}+\frac{3}{14}\] \[{{v}_{2}}=70cm\]right of second lens.
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