What is atmospheric refraction? Use this phenomenon to explain the following natural events:
a) Twinkling of stars
b) Advanced sunrise and delayed sunset
Draw diagrams to illustrate your answer.
Atmospheric refraction is the refraction of light caused by the earth's atmosphere due to change in the refractive indices of different layers of the atmosphere.
a) Twinkling of stars: Stars are distant point sourced sources of light. The path of the rays of light comig f=coming from the distant star goes on varying due to atmospheric refraction slightly. Thus, apparent position of the star fluctuates and the amount of star light entering the eye flickers giving the twinkling effect.
b) Advanced sunrise: When the sun is slightly below the horizon, light rays coming from the sun travel from rarer to denser layers of air. As a result of the atmospheric refraction of light. light appears to come from a higher position above the horizon. Therefore, the sun appears earlier than actual sunrise.
Delayed sunset: During sunset, the apparent position of the sun is visible to us and not the actual position due to the same bending of light rays effect. Therefore, because of refraction, we see the sunset afterwards although it has actually moved from its position.
A student is unable to see clearly the words written on the blackboard placed at a distance of approximately 4 m from him. Name the defect of vision the boy is suffering from. Explain the method of correcting this defect. Draw ray diagram for the:
(i) defect of vision and also
(ii) for its correction.
Write the importance of ciliary muscles in the human eye. Name the defect of vision that arises due to gradual weakening of the ciliary muscles. What types of lenses are required by the person suffering from this defect to see the objects clearly?
Akshay, sitting in the last row in his class, could not see clearly the words write on the blackboard. When the teacher noticed it, he announced if any student sitting in the front row could volunteer to exchange his seat with Akshay. Salman immediately agreed to exchange his seat with Akshay. He could now see the words written on the blackboard clearly. The teacher thought it fit to send the message to Akshay’s parents advising them to get his eyesight checked.
In the context of the above event, answer the following questions:
(a) Which defect of vision is Akshay suffering from? Which type of lens is used to correct this defect?
(b) State the values displayed by the teacher and Salman.
(c) In your opinion, in what way can Akshay express his gratitude towards the teacher and Salman?
(a) A person cannot read newspaper placed nearer than 50 cm from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.
(b) We see advertisements for eye donation on television or in newspapers. Write the importance of such advertisements.
