CBSE Class 10 Science The Human Eye and the Colourful World Assignment Set B

Question : The colored light that refracts most while passing through a prism is
a. Yellow
b. Violet
c. Blue
d. Red
Answer : B  

Question : Stars appears to be twinkling because of
a. atmospheric refraction
b. reflection
c. Tyndall effect
d. spectrum
Answer :  B

Question : After tracing the path of a ray of light through a glass prism a student marked the angle of incidence (∠i), angle of refraction (∠r), angle of emergence (∠e) and the angle of deviation (∠D) as shown in the diagram. The correctly marked angles are:

a. ∠i and ∠r
b. ∠i and ∠e
c. ∠i, ∠e and ∠D
d. ∠i, ∠r and ∠e
Answer : C

Question : What would have been the colour of the sky, if the Earth had no atmosphere? 
Answer : If the earth has no atmosphere, the sky would have appeared black because of no refraction.

Question : Why is red color selected for danger signal lights?
Answer :  Because the red light has the largest wavelength of all colors, it is the least dispersed. Because of this, much of the light gets reflected back and can travel longer distances through clouds, fog, dust etc. to effectively enter our eyes. 

Question : Light of two colors A and B pass through a glass prism. A deviates more than B from its path of incidence. Which color has a higher speed in the prism?
Answer :  Color B has higher speed than that of color A. 

Question :  How is the sense of vision carried from the eye to the brain? 
Answer :  Optic nerves carry sensation of vision from eye to brain.

Short Answer

Question : Explain with the help of a diagram, how we are able to observe the sunrise about two minutes before the Sun gets above the horizon
Answer :  The Sun can be seen about two minutes before sunrise because when the Sun is slightly below the horizon, the Sun’s light coming from less dense air to more dense air is refracted downwards as it passes through the atmosphere. Thus due to this atmospheric refraction, the Sun appears to be raised above the horizon when actually it is slightly below the horizon.

Question : Explain why the planets do not twinkle but the stars twinkle?
Answer :  The planets are much closer to the earth. A planet can be considered as a collection of large number of point-sized sources of light. So the total variation in the amount of light entering our eye from all the individual point-sized sources will average out to zero thereby nullifying the twinkling effect.

Long Answer

Answer : Here, u = - 25 cm (Normal near point)

v = -1 m = -100 cm (Near point of defective eye)

f=?

Using lens formula,

We see a beautiful band of seven colours on the screen called visible spectrum.

The sequence of colours seen from the lower part of the screen is violet (V), indigo

(I), blue (B), green (G), yellow (Y), orange (O) and red (R). The acronym for this is VIBGYOR.

 

 

 

Red light has the maximum wavelength and violet light has the minimum wavelength, so in a transparent medium except air and vacuum, red light having the largest wavelength suffers the least deviation while violet light having the least wavelength bends the most.