Class 10 Science Chapter 10 Question Answers - Human Eye and Colourful World

Q1: Why is the colour of the clear sky blue? (NCERT Exemplar)
Ans:

• Colour of the clear sky is blue: The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light.
• When sunlight passes through the atmosphere, the fine particles in air scatter the blue colour more strongly than red.

Q2: Why do stars appear to twinkle?
Ans: Stars appears to twinkle due to atmospheric refraction.

Q3:  Define farthest point of an eye.
Ans: Farthest point of an eye: The farthest point upto which the eye can see objects clearly is called far point of the eye. It is infinity for normal eye.

Q4: Define power of accommodation.
Ans: Power of accommodation: The ability of the eye lens to adjust its focal length is called accommodation.

Q5: Define least distance of distinct vision.
Ans: Least distance of distinct vision: Minimum distance at which an object can be seen distinctly without any strain from the normal eye, i.e., 25 cm for normal vision.

Q6: Define Tyndall effect.
Ans: Tyndall effect: The phenomenon of scattering of light by colloidal particles gives rise to Tyndall effect.
Tyndall effect can be observed when sunlight passes through a canopy of a dense forest. Here tiny droplets in mist scatters light.

Q7: Define atmospheric refraction.
Ans: Atmospheric refraction: If physical conditions of the refracting medium (air) are not stationary, the apparent position of the object fluctuates.

Q8: Why are danger signal lights red in colour?
Ans: Danger signal lights are red in colour because red colour is least scattered by fog or smoke.