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प्रश्न
Explain how Corpuscular theory predicts the speed of light in a medium, say, water, to be greater than the speed of light in vacuum. Is the prediction confirmed by experimental determination of the speed of light in water? If not, which alternative picture of light is consistent with the experiment?
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उत्तर
No; Wave theory
Newton’s corpuscular theory of light states that when light corpuscles strike the interface of two media from a rarer (air) to a denser (water) medium, the particles experience forces of attraction normal to the surface. Hence, the normal component of velocity increases while the component along the surface remains unchanged.
Hence, we can write the expression:
c sin i = v sin r ...........(i)
Where,
i = Angle of incidence
r = Angle of reflection
c = Velocity of light in air
v = Velocity of light in water
We have the relation for a relative refractive index of water with respect to air as:
μ = `"v"/"c"`
Hence, equation (i) reduces to
`"v"/"c" = sin"i"/sin "r" = μ` ..........(ii)
But, μ > 1
Hence, it can be inferred from equation (ii) that v > c. This is not possible since this prediction is opposite to the experimental results of c > v.
The wave picture of light is consistent with the experimental results.
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संबंधित प्रश्न
Let us list some of the factors, which could possibly influence the speed of wave propagation:
(i) Nature of the source
(ii) Direction of propagation
(iii) Motion of the source and/or observer
(iv) Wavelength
(v) Intensity of the wave
On which of these factors, if any, does the speed of light in vacuum?
Light waves travel from optically rarer medium to optically denser medium. Its velocity decreases bec;ause of change in ______.
The optical properties of a medium are governed by the relative permittivity (εr) and relative permeability (µr). The refractive index is defined as `sqrt(µ_r ε_r) = n`. For ordinary material εr > 0 and µr > 0 and the positive sign is taken for the square root. In 1964, a Russian scientist V. Veselago postulated the existence of material with εr < 0 and µr < 0. Since then such ‘metamaterials’ have been produced in the laboratories and their optical properties studied. For such materials `n = - sqrt(µ_r ε_r)`. As light enters a medium of such refractive index the phases travel away from the direction of propagation.
- According to the description above show that if rays of light enter such a medium from air (refractive index = 1) at an angle θ in 2nd quadrant, them the refracted beam is in the 3rd quadrant.
- Prove that Snell’s law holds for such a medium.
In the figure, the optical fibre is l = 2 m long and has a diameter of d = 20 µm. If a ray of light is incident on one end of the fibre at angle θ1 = 40°, the number of reflections it makes before emerging from the other end is close to:
(Refractive index of fibre is 1.31 and sin 40° = 0.64)
A glass slab of thickness 4 cm contains the same number of waves as 5 cm of water. When both are traversed by the same monochromatic light. If the refractive index of water is `(4/3)`. What is that of glass?
White light is an incident at 20° on a material of silicate flint glass slab as shown. `μ_"violet"` = 1.66 and µr = 1.6. For what value of d will the separation be 1 mm in red and violet rays?
Using Huygens’s construction of secondary wavelets draw a diagram showing the passage of a plane wavefront from a denser to a rarer medium. Using it verifies Snell’s law.
What is the direction of the refracted ray relative to the refracted wavefront?
Which refractive index corresponds to medium 1?
Which equation is Snell's law of refraction for media 1 and 2?
When a light wave travels from one medium to another, which property remains the same?
How are the wavelengths in the two media related to the speeds of light in those media?
What happens to the wavelength of light when it goes from a rarer to a denser medium?
How does the speed of light in a denser medium compare with its speed in a rarer medium?
