Ray Optics

JEE Main level, numerical answer, medium

133 of 295

Question 133 of 295

A collimated beam of light of diameter 2 mm is propagating along xx-axis. The beam is required to be expanded in a collimated beam of diameter 14 mm using a system of two convex lenses. If first lens has focal length 40 mm, then the focal length of second lens is ____\_\_\_\_ mm.

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Answer: 280

For beam expander using two convex lenses:
Magnification =d2d1=f2f1= \frac{d_2}{d_1} = \frac{f_2}{f_1}
142=f240\frac{14}{2} = \frac{f_2}{40}
f2=7×40=280f_2 = 7 \times 40 = 280 mm

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