This set of Physics Exam Questions for IIT JEE Exam focuses on “Ray Optics – Natural Phenomena due to Sunlight”.
1. Which among the following relates scattering and wavelength of the particle?
a) Rayleigh scattering
b) Photon scattering
c) Wave theory
d) Cauchy’s formula
Explanation: Light of shorter wavelengths is scattered much more than light of longer wavelengths. The amount of scattering is inversely proportional to the fourth power of the wavelength. This is known as Rayleigh scattering.
2. Which one of the following is not an illustration of the scattering of light?
a) The blue color of the sky
b) The white color of the clouds
d) The red color of danger signals
Explanation: A rainbow is an example of a dispersion of sunlight by the water drops in the atmosphere. This is a phenomenon due to the combined effect of dispersion, refraction, and reflection of sunlight by spherical water droplets of rain. Others all are common illustrations of scattering of light.
3. How many kinds of rainbows are there, generally?
Explanation: Generally, there are two kinds of rainbows, namely primary rainbow and secondary rainbow. The primary rainbow occurs due to one internal reflection and two refractions, whereas secondary rainbow occurs due to two internal reflections and two refractions, from the water drops suspended in the air.
4. The secondary rainbow is fainter than the primary rainbow.
Explanation: Yes, the secondary rainbow is fainter than the primary rainbow. As the secondary rainbow is formed by one more reflection than the primary rainbow, it is much fainter than the primary rainbow. The colors are also reversed in the secondary rainbow. In the primary rainbow, the violet color is on the inner edge and red color is on the outer edge. It is the other way round for the secondary rainbow.
5. Find the wrong statement.
a) Clouds appear white for most of the day because the sun radiates all visible wavelengths of light
b) The rays have to travel a shorter distance than usual at sunrise and sunset
c) Danger signals are red because red color gets scattered the least
d) The sky is blue because blue light is scattered more than other colors since it travels as shorter waves
Explanation: During sunrise and sunset, the rays have to travel a large part of the atmosphere since the rays are close to the horizon at that time. That is why, red being the least scattered enters our eyes, as all the other colors get scattered away.
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