Geometrical OpticsHard
Question
A converging beam of rays is incident on a diverging lens. Having passed through the lens the ray intersect at a point 15 cm from the lens on the opposite side. If the lens is removed the point where the rays meet will move 5 cm closer to the lens. The focal length of the lens is
Options
A.5 cm
B.- 10 cm
C.20 cm
D.- 30 cm
Solution
Here, v = + 15 cm, u = + (15 - 5) = + 10 cm
According to lens formula
⇒ 
f = - 30 cm.
According to lens formula
⇒ f = - 30 cm.
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