Assertion and Reason for Ch 10 Human Eye and The Colorful World Class 10 Science
Important QuestionsA
Answer
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
1
Reason (R): Blue colour has shortest wave length in visible spectrum.
Answer
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
During the day time, sky appears blue. This is because the size of the particles in the atmosphere is smaller than the wavelength of visible light, so they scatter the light of shorter wavelengths. The scatter blue light enters our eye.
2
Reason (R): The eye is producing too much divergence in the incident beam.
Answer
(c) Assertion (A) is true but reason (R) is false.
The light from a distant object arriving at the eye lens may get converged at a point in front of the retina. This type of defect is called near-sightedness or myopia. This means that the eye is producing too much convergence in the incident beam.
3
Reason (R): Myopia can be corrected by using spectacles made from concave lenses.
Answer
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
In Myopia eye due to the increased converging power of eye lens, the image of a far off object is formed in front of the retina.
Myopia can be corrected by using spectacles made from concave lens.
4
Reason (R): For a prism material, refractive index is highest for red light and lowest for the violet light.
Answer
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
The light of violet colour deviates most and the light of red colour the least, while passing through a prism. For a prism material refractive index is highest for violet light and lowest for the red light.
5
Reason (R): Secondary rainbow formation is three step process and hence, the intensity of light is reduced at the second reflection inside the rain drop.
Answer
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
Primary rainbow is a result of three-step process.
1. Refraction at the first surface of raindrop.
2. Total internal reflection from the second surface of raindrop.
3. Again refraction from the first surface of raindrop from where the light finally emerges out. The intensity of light is reduced at the second reflection and hence, the secondary rainbow is fainter than the primary rainbow.
6
Reason (R): The stars are much bigger in size than the planets.
Answer
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
As planets are of larger size than stars and much closer to the earth, planets can be considered as a collection of large number of point sized sources of light. The total variation in the amount of light entering our eye from all these individual point sized sources will average out to zero which nullify the twinkling effect of each other. Therefore, planets do not twinkle.
7
Reason (R): If the magnification of a system is less than one, then the image formed is inverted.
Answer
(c) Assertion (A) is true but reason (R) is false.
The image formed on retina is real and inverted. If magnification is less than 1, then diminished images is formed not inverted.
8
Reason (R): The optical instruments are used to increase the visual angle.
Answer
(d) Assertion (A) is false but reason (R) is true.
Optical instruments do not increase the size of the image of the object. It depends upon the distance between the object and objective lens.
9
Reason (R): Dispersion takes place due to variation of refractive index for different wavelength but in vacuum the speed of light is independent of wavelength and hence vacuum is a non-dispersive medium.
Answer
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
In vacuum speed of light is independent of wavelength, Hence, no dispersion takes places in vacuum. Thus, vacuum is a non-dispersive medium in which all colours travel with the same speed.
10
Reason (R): The angle between the refracted ray and normal to the drop surface is greater than the critircal angle.
Answer
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
The rainbow is formed when light at the inner surface of the water drop gets internally reflected if the angle between the refracted ray and normal to the drop surface is greater than the critical angle.