Advertisements
Advertisements
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?
Advertisements
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.
APPEARS IN
संबंधित प्रश्न
Given below is a diagram showing a defect of human eye. Study it and answer the following questions.
(i) Name the defect shown in the figure.
(ii) Give reason for this defect of eye in human being.
(iii) Name the type of lens used to correct the eye defect.
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 man can read the number of a distant but clearly but he finds difficulty in reading a book.
What type of spectacle lens should he use to correct the defect?
Describe the mechanism of focusing the image of a distant object in your eye when you raise your head after reading a book.
Given below is a diagram depicting a defect of the human eye. Study the same and answer the question that follow:
Name the defect shown in the diagram.
A person is unable to read a book placed closer than 1 meter from his eyes. Identify the defect of vision in his eyes. Draw the ray diagrams to show the defect of vision and its correction.
Distinguish between the following pair of words:
Myopia and hypermetropia
The near point of the eye of a person is 50 cm. Find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25 cm from the eye?
Give Reason:
When you enter into a dark room from bright because of sunlight, you can not see things for a few seconds.
Complete the following sentence with appropriate word :
An inability to focus on nearby objects due to loss of elasticity of the lens with age is called Iris.
