The sun is visible to us a few minutes before the actual sunrise because of:
Correct Answer:
(D)
Refraction of light
Due to the refraction of light, the sun is visible to us a few minutes before sunrise and a few minutes after sunset.
Ques: 2
The sun and the moon appear elliptical near the horizon because of:
Correct Answer:
(A) Refraction
The sun and the moon appear elliptical near the horizon because of refraction.
Ques: 3
Red light is used in traffic signals because
Correct Answer:
(A) It has the longest wavelength.
The wavelength of red colour is highest while of violet colour is lowest. Dispersal is inverse to wavelength so red light can be seen from far away clearer. That's why the red colour is used in traffic signals.
Ques: 4
Assertion (A): The danger signal is made up of red colour.
Reason (R): Red colour is scattered the least.
Select the correct answer using the codes given below:
(A) and (R) are true and (R) is the correct explanation of
(A).
Correct Answer:
(A) and (R) are true but (R) is not the correct explanation of
The primary reason why the red colour is used for danger signals is that red light has the highest wavelength and is scattered least by air molecules so that it can be seen from far away. The appearance of the red colour of sun at the sunset is due to the fact that neighbouring colours are scattered away in the path and light reaching the observer is predominantly red. That is why the sun is seen red to us.
Ques: 5
The Sky appears blue due to –
Correct Answer:
(A) Blue color is scattered most
The blue appearance of the sky is due to scattering of sunlight from the atmosphere. When we look at the sky, it is the scattered light which enters the eyes. Among the shorter wavelengths, the blue colour is present in a larger proportion in sunlight. Light of shorter wavelength is scattered by air molecules which because of their smaller size follow Rayleigh's scattering. Blue light is strongly scattered by the air molecules and reaches the observer. This explains the blue colour of the sky.
Ques: 6
Consider the following statements:
The Sky appears blue because of scattering.
The main cause of seven colors of the rainbow is scattering of light.
At the time of sunrise, the sun appears red, due to scattering of light.
Choose the correct statement/s from the given options:
Correct Answer:
(B) 1 and 3 is true
The intensity of scattered light is inversely proportional to its wavelength and the wavelength of violet and blue is low, thus they scattered more. This is the main cause for the blue colour of the sky. As we know that sunlight consists of seven colours, of these, red has the maximum wavelength. During sunrise and sunset, the rays have to travel a larger part of the atmosphere because they are very close to the horizon. Therefore, light other than red is mostly scattered away. Most of the red light which is least scattered enters our eyes. Hence, the sun appears red. The rainbow is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. Thus, statements 1 and 3 are correct.
Ques: 7
Sea seems blue due to –
Correct Answer:
(B) Reflection of sky and scattering of light by the drops of water
The sea looks blue due to reflection of sky and scattering of light by the drops of water. Light scattered as it passes through air or water. Since blue light has a short wavelength, it scatters most easily.