A) + 1.5 D
B) - 1.5 D
C) + 6.67 D
D) - 6.67 D
Correct Answer: B
Solution :
\[Power=\frac{1}{focal\,length}\]Focal length of combination of convex and concave lens is given by \[\frac{1}{F}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}\]where \[{{f}_{1}}\] and \[{{f}_{2}}\]be the focal lengths of convex and concave lenses respectively. Now, \[\frac{1}{F}=\frac{1}{0.4}+\frac{1}{(-0.25)}\] \[Power\,P=-1.5\,D\]
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