Question

A beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12 cm from P. At what point does the beam converge if the lens is (a) a convex lens of focal length 20 cm, and (b) a concave lens of focal length 16 cm?

Solution
Verified by Toppr

(a). According to the given case, object is virtual, u=+12 cm
The focal length of the convex lens is f=+20 cm.
Using lens equation, 1v1u=1f

1v112=120

v=7.5 cm

(b). Now the focal length of the concave lens, f=16 cm
1v1u=1f

1v112=116

v=48 cm

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