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JEE Main 202621 JanuaryMorning Shift
Exam
JEE Main
Year
2026
Date
21 January
Shift
Morning Shift
Subject
Physics
Chapter
Ray Optics

JEE Main 2026 · 21 January · Morning Shift · Physics · Ray Optics

A collimated beam of light of diameter 2 mm is propagating along x...

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.

Correct answer

280

Step-by-step solution

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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