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प्रश्न
By closing the eyes and gently pressing them by your palms, you may see some specks of brilliant light. How do you get this sensation while there is no light entering your eyes?
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उत्तर १
If we look at a bright object and then close our eyes, the sensation of light persists for a short period of time. This is known as the persistence image or the after image. It lasts for one-tenth of a second. Therefore, by closing your eyes and gently pressing them with your palms, you see some specks of brilliant light.
उत्तर २
Phosphenes are the sense of seeing dazzling light after gently touching the eyes with your palms. Mechanical activation of retinal cells causes this behaviour, even when no external light is present. This is how it happens:
- Mechanical Stimulation: Closing your eyes and lightly pressing them with your palms applies pressure to the eyeballs.
- Stimulation of Retinal Cells: Pressure on the eyeballs stimulates retinal cells, including photoreceptors (rods and cones).
- Activation of the Optic Nerve: Stimulated retinal cells transmit messages to the brain via the optic nerve.
- Perception of Light: The brain interprets these signals as light, resulting in the impression of phosphenes, or dazzling light.
Mechanical stimulation mimics the impact of light on the retina, creating a sense of light even when no external light enters the eyes. Other ways to create phosphenes include rubbing your eyes or being exposed to strong magnetic fields.
Notes
Students can refer to the provided solutions based on their preferred marks.
संबंधित प्रश्न
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?
Explain two possible reasons of myopia. How can it be corrected? Explain with a suitable diagram.
What is the scientific name of
long-sightedness?
A person can read a book clearly only if he holds it at an arm's length from him. Name the defect of vision:
if the person is an old man
Have a look at the posture of this girl who is reading a book and answer the questions which follow:
Name the problem she is facing.
Select the odd one in the following series:
Endolymph, Tympanic membrane, Semi-circular canal, Blind spot.
Write whether the following is true or false:
A convex lens is used for correcting myopia.
Have a look at the posture of this woman who is reading a book and answer the questions which follow:
What kind of looking glasses she needs?
Differentiate between:
Myopia and Hypermetropia.
Correlate the given sequence:
Hypermetropia : Convex lens : ______ : Concave lens
