Respuesta :
The focal length of lens in water is 23.75cm if focal length of same lens in air is 79cm and refractive index is 1.55
Delineation of the frequency and refraction points. The refractive file decides how much the way of light is bowed, or refracted, while entering a material. This is depicted by Snell's law of refraction, n1 sin θ₁ = n2 sin θ₂, where θ1 and θ2 are the point of frequency and point of refraction, separately, of a beam crossing the connection point between two media with refractive records n1 and n2.
The refractive records likewise decide how much light that is reflected while arriving at the point of interaction, as well as the basic plot for all out inward reflection, their power (Fresnel's conditions) and Brewster's angle.
According to lens maker's formula, we know that
1/f=(μ-1)(1/R₁-1/R₂)
where f is the focal length of lens and μ is refractive index ,and R₁,R₂ are the radius of given lens.
For focal length in air
=>1/f₁=(1.55-1)(1/R₁-1/R₂)-----eq1
Now, for focal length in water
=>1/f₂=(1.55/1.33-1)(1/R₁-1/R₂)------eq2
On dividing eq2 by eq1,we get
=>f₁/f₂ = [(1.55-1)×1.33] / (1.55-1.33)]
=>79 / f₂ =[(0.55)×1.33] / (0.22)]
=> f₂ =79 / [(0.7315/0.22)]
=> f₂ = 79/3.325
=>f₂ =23.75cm
Hence, focal length in water is 23.75cm.
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