Worksheet solutions for chapter: Light for class 8 are provided below.
(1) What is blind spot? How will you demonstrate it?
Blind spot is the spot where no vision is possible. In our eyes at the joint of the optic nerve and the retina there no sensory cells which can send images to the brain to interprets for us.
Demonstration for blind spot
Mark a cross and a circle at the distance of 6 – 8 cm in between them. Now, hold paper at the arm length. Close your left eye. Look continuously at the cross while moving sheet towards eyes. The cross will disappear. Now close your right eye and look continuously at the round spot while moving sheet towards eyes. The round mark will disappear. It shows that there is a point on the retina which cannot send messages to the brain when light falls on it.
(2) What is cataract? How will we correct it?
Cataract is a problem of no or incorrect vision of our eyes when lens become foggy. The problem of cataract can be corrected by inserting new artificial lens and removing opaque original lens.
(3) Who are called visually challenged persons. How can they read and write?
Visually challenged persons cannot see or have less vision but they develop their other senses more sharply. They identify things by touching and listening to voices more carefully.
Braille system is developed for the visually challenged persons to help them read and write.
(4) What are the optical aids?
Optical aids are used to correct the vision of the humans. Optical aids include bifocal lenses, contact lenses, tinted lenses, magnifiers and telescopic aids.
(5) Identify incident ray, reflected ray, normal, point of incidence, angle of incidence, angle of reflection and labelled them in figure below.
The required labelles are marked on the given figure and presenting below-
(6) Fill in the blanks:-
(i) The most popular resource for visually challenged persons is ____.
(ii) The impression of an image persists in retina for about _____ of a second.
(iii) _____ can look all around.
(iv) ____ is responsible for the colour of our eyes.
(i) The most popular resource for visually challenged persons is Braille method.
(ii) The impression of an image persists in retina for about 1/16th of a second.
(iii) Crab can look all around.
(iv) Iris is responsible for the colour of our eyes.
(7) What is dispersion?
Dispersion is the splitting of the light into its seven colours.
(8) Ram performed a test to check law of reflections. He shows his results to his teacher. The teacher marked it wrong. The figure of his test is giving below. Why the teacher marked wrong his result.
The teacher marked the results wrong because angle of incident and angle of reflection measured different. According to law of reflection both should be equal.
(9) In the changing room we can see our multiple images. How it could happen?
When two or more plane mirrors set at different angles, they got multiple reflections from different mirrors. Therefore, in the changing room plane mirrors are set at different angles and we get multiple images.
(10) Choose the correct one from the given answers.
Day birds have
(i) more cones and fewer rods.
(ii) more cones and more rods
(iii) less cones and more rods
(i) more cones and fewer rods.