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Worksheetspower of lens
Total questions: 8
Worksheet time: 16mins
A lens is formed by combining two thin lenses of powers + 12 D and – 8 D in contact with each other. What will be the focal length of combination ?
24.9
30
25
29
. An optician prescribes spectacles to a patient with a combination of a convex lens of focal length 40 cm and a concave lens of 25 cm focal length. What will be the power of spectacles
-1.5
2.5
-1.4
1.54
A convex lens of power +4 D and a concave lens of power 3 D are placed in contact. What is equivalent power of the combination ?
1
2
3
4
A convex lens has focal length of 20 cm. find its power in Dioptres.
4
2
5
9
The combined power of two lenses in contact is + 10 D. When they are separated by 20 cm, their power becomes 6.25 D. Find the power of individual lenses.
7.5 , 2.5
8 ,7
9,5
7.5,2.4
A lens made of glass of refractive index 1∙5 has power of + 10 D when placed in air, find the power of same lens when immersed in water (µ = 1∙33). Also find the change in power of lens.
6.7
-7.5
1.33
8
An optician prescribes spectacles to a patient with a combination of a convex lens of focal length 40 cm and concave lens of 25 cm. The power of spectacles is
6
-6
1.5
-1.5
The power of a lens is +2.0D find its focal length and state the kind of a lens
50 and convex
50 and concave
90 and convex
90 and concave
