A convex lens of focal length 25 cm is placed in contact with a concave lens of focal length 20 cm what is the power of combination ? what is the nature of combination
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dimpy215:
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focal length of concave lens = -25 cm = -25 /100 m power = P₁ = 1/-25/ 100 = -4 D
focal length of convex lens = +20 cm = 20/100 m power = P₂ = 1/20/100 = 5 D
So net power = P = P₁ + P₂ = -4 D + 5D = 1 D (implies combination behave as convex lens).
Hope this solution is correct
focal length of convex lens = +20 cm = 20/100 m power = P₂ = 1/20/100 = 5 D
So net power = P = P₁ + P₂ = -4 D + 5D = 1 D (implies combination behave as convex lens).
Hope this solution is correct
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2
Answer:
Given that
Focal length of a convex lens,F1=25
Focal length of a concave lens,F2=20
power of a convex lens,P1=100/F1
=100/25
=+4D
now,
power of a concave lens,P2=100/20
=-5D
therefore,
i)power of combination,P3=P1+P2
=-5+(4)
=-1
ii)focal length of combination=F1+F2
25-20
=5cm
Since,power =-1
There fore, the image will be virtual and erect
Thank you
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