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water(with refractive index) = 4/3 in a tank is 18cm deep . oil of refractive index 7/4 lies on water making a convex surface of radius of curvature R = 6 cm as shown , consider oil to act as a this lens. an object S is placed 24 cm above water surface. the location of its image is at x cm above the bottom of the tank then x is

water(with refractive index) = 4/3 in a tank is 18cm deep . oil of refractive index 7/4 lies on water making a convex surface of radius of curvature R = 6 cm as shown , consider oil to act as a this lens.  an object S is placed 24 cm above water surface.  the location  of its image is at x cm above the bottom of the tank  then x is

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1 Answers

Aman Bansal
592 Points
12 years ago

Dear Sanjay,

he law of distances in the case of refraction at an interface between two media of refractive indices n1and n2 is

n2/v – n1/u = (n2 – n1)/R where ‘v’ is the imagedistance, ‘u’ is the object distance and ‘R’ is the radius of curvature of the refracting surface. In the case of the refraction at the air-oil interface we have n2 = 7/4, n1 = 1, u = – 24 cm and R = 6 cm. so that

7/4v – 1/(– 24) = [(7/4) –1]/6

Therefore, 7/4v = 3/24 – 1/24 = 1/12

This gives v = 21 cm.

The image formed (at 21 cm from the oil surface) by the refraction at the air-oil interface will act as a virtual object for the refraction at the oil-water interface so that u = 21 cm (positive according to Cartesian sign convention). In this case n2 = 4/3, n1 = 7/4 and R = ∞.

[The radius of curvature is infinity since the oil-water interface is plane].

Therefore we have

4/3v1 – 7/(4×21) = [(4/3) – (7/4)]/∞ where v1 is the distance of the final image (from the water surface).

Or, 4/3v1 – 7/(4×21) = 0

This gives v1 = 16 cm.

The water column in the tank has a height of 18 cm. Therefore the final image is 2 cm above the bottom of the tank.

Therefore, x = 2 

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Aman Bansal

Askiitian Expert

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