An equiconvex lens (of refractive index 1.50) in contact with a liquid...
Problem:
An equiconvex lens (of refractive index 1.50) in contact with a liquid layer on top of a plane mirror. A small needle with its tip on the principal axis is moved along the axis until its inverted image is found at the position of the needle. The distance of the needle from the lens is measured to be 45.0cm. The liquid is removed and the experiment is repeated. The new distance is measured to be 30.0cm. What is the refractive index of the liquid? Explain in details.
Solution:
Step 1: Understand the Problem
The problem deals with the measurement of the refractive index of a liquid. The refractive index of the lens is given as 1.50. The experiment involves finding the position of the inverted image of a needle placed on the principal axis of the lens. The needle is first placed at a distance of 45.0cm from the lens when the liquid is present and then at a distance of 30.0cm when the liquid is removed. The refractive index of the liquid needs to be calculated.
Step 2: Identify the Relevant Formula
The relevant formula for this problem is the lens formula:
1/f = 1/v - 1/u
where f is the focal length of the lens, v is the distance of the image from the lens, and u is the distance of the object from the lens.
Step 3: Apply the Formula
Let the refractive index of the liquid be n and the radius of curvature of the lens be R. When the needle is placed at a distance of 45.0cm from the lens, we can write:
1.50 = (n-1) (1/R - 1/(-R))
1.50 = (n-1) (2/R)
1/R = (n-1) (2/1.50R)
R = 2nR/3 - 2R/3
u = -45cm, v = -45cm
1/f = (n-1) (1/R)
1/f = (n-1) (3/2nR)
f = 3R/2(n-1)
1/v - 1/u = 1/f
1/v - 1/-45 = 2(n-1)/3nR
v = -90nR/(3n-2)
When the liquid is removed and the needle is placed at a distance of 30.0cm from the lens, we can write:
1.50 = (1/R)
R = 2/3 cm
u = -30cm, v = -30cm
1/f = (1/R)
f = R
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