A ray of light enters a glass prism from air. Which change occurs to the speed of the light as it enters the prism?
The speed of light decreases inside the prism
Light travels fastest in vacuum (about \(3 \times 10^8\) m/s, nearly the same in air). Glass is optically denser, with refractive index about 1.5.
Refractive index \(n = \frac{c}{v}\), so the speed of light in glass is \(v = \frac{c}{n} \approx \frac{3 \times 10^8}{1.5} = 2 \times 10^8\) m/s. When light passes from air into the prism its speed decreases, and that is why the ray bends towards the normal.
Light can never move infinitely fast; its speed does not stay unchanged, because the two media have different refractive indices; and it would increase only on going from a denser to a rarer medium, such as glass to air.
Hence, the speed of light decreases inside the prism.
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Important Questions from Optics
Who was the first one to use a glass prism to obtain the spectrum of sunlight?
Twinkling of stars is due to:
In which a convex mirror is used?
A. Rear View mirrors in vehicles
B. Glass windows
C. Makeup Mirror
D. Kaleidoscope
An object is placed 10 cm in front of a lens. The image formed is real, inverted and of same size as the object. What is the focal length and nature of the lens?
The power of a lens is -2.5 D. The type of lens and its focal length are respectively:
