(a) A student is unable to see clearly the words written on the black board placed at a distance of…
(a) A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.
(b) Why do stars twinkle? Explain.
Solution
(a) He is suffering from myopia. Causes of myopia:
(i) elongation of eye ball.
(ii) excessive curvature of cornea. Concave lens of suitable power is used to correct myopia.
(b) Light coming from stars when enter in the Earth’s atmosphere suffers refraction from the atmospheric layers. Since the densities of atmospheric gases changes frequently. Since the stars are point sized and at a far distance so sometimes star appear brighter and sometimes dimmer which gives the impression as the stars twinkling.