It was a bright, sunny day in the morning when the classes started in the school. Suddenly dark clouds appeared in the sky. Due to this the classroom became quite dark. The teacher asked a student to switch on all the lights in the classroom.
(a) Why did the teacher ask for all the lights to be switched on ?
(b) What was the size of the pupil of the eyes of the students :
(i) before the clouds appeared ?
(ii) when classroom became quite dark ?
(iii) when the lights were switched on ?
(c) In which of the above mentioned three situations, the students will feel glare in their eyes and why ?
(d) What values are exhibited by the teacher in this case ?

Explanation

(a) The teacher asked all the lights in the classroom to be switched on because seeing the blackboard writing in dim light put a lot of strain on the eyes of the students.
(b) (i) Before the clouds appeared, there was sufficient light in the classroom due to which the size of pupil of eyes was small.
(ii) When classroom became quite dark, the light was dim, due to which the size of pupil of eyes was very large.
(iii) When the lights were switched on, the light was bright and hence the size of pupil of eyes became small again.
(c) The students will feel glare in their eyes when the lights are switched on in the dark classroom. This is because the size of pupil of eye is large in the dark room. So, when lights are switched on, then suddenly too much light enters the eyes (due to large size of pupil) causing the glare in the eyes.
(d) The values exhibited by the teacher are (i) General awareness or Knowledge (that it is necessary to study in sufficient light to keep the eyes healthy, and (ii) Concern for the students (that studying in dim light can harm the eyes of students).