Advertisements
Advertisements
Question
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?
Advertisements
Solution
The speed of light in a vacuum i.e., 3 × 108 m/s (approximately) is a universal constant. It is not affected by the motion of the source, the observer, or both. Hence, the given factor does not affect the speed of light in a vacuum.
RELATED QUESTIONS
Is the speed of light in glass independent of the colour of light? If not, which of the two colours red and violet travels slower in a glass prism?
The wavefronts of a light wave travelling in vacuum are given by x + y + z = c. The angle made by the direction of propagation of light with the X-axis is _________ .
The wavefronts of light coming from a distant source of unknown shape are nearly _________ .
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)
In the given figure, the face AC of the equilateral prism is immersed in a liquid of refractive index 'n'. For incident angle 60° at the side AC, the refracted light just grazes along face AC. The refractive index of the liquid n = `sqrtx/4`. The value of x is ______.
(Given refractive index of glass = 1.5)
A light ray in a medium (RI = 5/3) enters another medium at an angle of 30°. The angle in the other medium is sin-1 (5/6). The incident angle must be increased such that the ray is completely reflected at minimum degrees is ______.
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.
In the refraction construction, which medium is assumed to be denser?
What is the direction of the refracted ray relative to the refracted wavefront?
What does \[\frac{\sin i}{\sin r}\] equal in terms of the speeds in the two media?
Which equation is Snell's law of refraction for media 1 and 2?
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?
Which picture of light was needed to address why its speed differs between media?
How does the wave picture's conclusion about the speed of light in a denser medium compare with that deduced from the particle picture?
