convex lens of focal length 0.2m is made of material of refractive index 7/2. The lens is placed in a medium, then its focal length is increased by 0.35 m. What is the refractive index of the medium?
Ops: A. 9/5
B. 11/6
C. 13/7
D. 57/22
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Answer:
answer of this question is option a
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Explanation:
Given Convex lens of focal length 0.2 m is made of material of refractive index 7/2. The lens is placed in a medium, then its focal length is increased by 0.35 m. What is the refractive index of the medium?
- So the focal length in air is 0.2 m and refractive index of the material is 7/2.
- So we have refractive index as μ / μa (in air)
- = 7/2/1
- = 7/2
- Now when the lens is placed in a medium we have
- μm
- So the focal length is increased by 0.35 m, so we get
- 0.2 + 0.35
- = 0.55 m
- From the lens maker’s formula we have
- 1/fa = (μ / μa – 1)(1/R1 – 1/R2) --------1
- Now in a medium we get
- 1/fm = (μ /μm – 1) (1/R1 – 1/R2) ---------2
- Equation 1 / 2 will give
- fm / fa = (μ / μa – 1) / (μ / μm – 1)
- 0.55 / 0.2 = (7/2 – 1) / (7/2 μm – 1)
- 55 / 20 = 5/2 / ((7/2 μm – 1)
- 11/4 (7/2 μm – 1) = 5/2
- 11/2 μm – 1 = 10/11
- 7/2 μm = 10/11 + 1
- = 21 / 11
- 6 μm = 11
- Or μm = 11 / 6
Reference link will be
https://brainly.in/question/10201406
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