a convex lens of focal length 25 cm and concave lens of focal length 10 cm are placed in clothes connects with each other calculate the length of this combination
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Explanation:
f1 = 25cm (Focal length of convex lens is positive)
⇒ f1 = 0.25m (1m = 100cm)
P (in dioptre) =
⇒ Power of convex lens,(F=25 cm) P1 =
⇒ P1 =
∴ P1 = 4D
f2 = -10cm (Focal length of concave lens is negative)
⇒ f2 = -0.1m (1m = 100cm)
⇒ Power of the concave lens(F=10 cm), P2 =
⇒ P2 =
∴ P2 = -10D.
Power of combination = P1 + P2.
P = 4D – 10D = -6D.
Lens power of the combination is -6D. Since it is negative therefore the new lens will behave like concave lens having a focal length of 16.6cm.
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