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?
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
Millions of people in the developing countries of the world are suffering from corneal blindness. These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society of your city has organised a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission, how would you contribute in this noble cause?
(i) State the objective of organising such campaigns.
(ii) List two arguments which you would give to motivate the people to donate their eyes after death.
(iii) List two values which are developed in the persons who actively participate and contribute in such programmes.
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.
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
What is the other name for
myopia
Name the body part with which the terms myopia and hypermetropia are connected.
Your friend can read a book perfectly well but cannot read the writing on blackboard unless she sits on the front row in class.
What type of lenses-converging or diverging-would an optician prescribe for her?
A man can read the number of a distant but clearly but he finds difficulty in reading a book.
From which defect of the eye is he suffering?
Differentiate between myopia and hypermetropia. What type of spectacles should be worn by a person having the defects of myopia as well as hypermetropia? How does it help?
A person suffering from the eye-defect myopia (short-sightedness) can see clearly only up to a distance of 2 metres. What is the nature and power of lens required to rectify this defect?
A short-sighted person has a near point of 15 cm and a far point of 40 cm.
(a) Can he see clearly an object at a distance of:
(i) 5 cm?
(ii) 25 cm?
(iii) 50 cm?
(b) To see clearly an object at infinity, what kind of spectacle lenses does he need?
Name an old age eye defect. What happens in it?
What is meant by optical illusion? Give one example.
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.
A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
Select the odd one in the following series:
Endolymph, Tympanic membrane, Semi-circular canal, Blind spot.
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?
Solve the following question:
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?
Differentiate between:
Short-sightedness and Long-sightedness.
Name the following:
Two kinds of accomodations.
