Chapter 6 : Ray Optics – Important 2 Mark Questions
Most Repeated 2 Mark Questions
Curated from Previous Year Question Papers
Define power of a lens. Give its unit.
The power of a lens is a measure of the degree of convergence or divergence the lens produces on the light falling on it.
The power of a lens P is the reciprocal of its focal length in metre.
The unit of power is dioptre (D) .
1 D = 1 m−1
Why does sky appear blue in colour?
During day time, violet colour which has the shortest wavelength gets scattered more than the other colours. The next scattered colour is blue.
As our eyes are more sensitive to blue colour than violet colour, the sky appears blue during day time.
What is Rayleigh’s scattering?
If the scattering of light is by atoms and molecules which have size a very much less than that of the wavelength λ of light (a << λ), then the scattering is called Rayleigh’s scattering .
State Rayleigh’s scattering law.
The intensity of light scattered in Rayleigh’s scattering is inversely proportional to the fourth power of wavelength .
Appeared Once Questions
Curated from Previous Year Question Papers
What is the reason for reddish appearance of sky during sunset and sunrise?
During sunrise and sunset, the light from the Sun travels a greater distance through the atmosphere .
Hence, the blue light which has shorter wavelength is scattered away and the red light which has longer wavelength and is less scattered manages to reach our eye.
This is the reason for the reddish appearance of the sky during sunrise and sunset.
What are the conditions to achieve total internal reflection?
Give the reason for the glittering of diamond.
Diamond appears dazzling because of the total internal reflection of light that happens inside the diamond.
The refractive index of diamond is about 2.417. It is much greater than the refractive index of ordinary glass, which is about only 1.5.
What is optical path?
Optical path of a medium is defined as the distance d′ light travels in vacuum in the same time it travels a distance d in the medium.
Hence,
State Snell’s law / Law of refraction.
The incident ray, refracted ray and normal to the refracting surface are all coplanar .
