A) convex, 12 cm
B) concave, 12 cm
C) convex, 6 cm
D) convex, 18 cm
Correct Answer: C
Solution :
Magnification \[m=\frac{v}{-u}=-3\] v = 3u = 30 cm Focal length of co-axial combination \[\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}=\frac{1}{v}-\frac{1}{u}\] \[-\frac{1}{30}+\frac{1}{{{f}_{2}}}=\frac{1}{30}+\frac{1}{10}=\frac{4}{30}\] \[\frac{1}{{{f}_{2}}}=\frac{4+1}{30}=\frac{5}{30}\] \[{{f}_{2}}=\frac{30}{5}=6\,cm\] Hence, lens A is convex lens.You need to login to perform this action.
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