Explain the structure and functioning of Human eye. How are we able to see nearby as well as distant objects?
Human Eye: The natural optical device through which one could see objects around him. It forms an inverted and real image on a light sensitive surface called the retina.
Parts of human eye are:
To see nearby as well as distant objects, ciliary muscles modify the curvature of eye lens. This leads to variation in focal length. When the muscles are relaxed, the focal length of the lens has its maximum value, equal to the distance from the retina. So, parallel rays coming into the eye get focussed on the retina. When the eye looks at nearby objects, the ciliary muscles are strained and the focal length decreases. So, that sharp image again forms on the retina.
How is the length of the telescope tube related to the distance between the objective and the eyepiece of the telescope? How can the magnification of the telescope be increased?
A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw ray diagram for the correction of this defect.
Give the condition required to achieve a larger magnification of a small object by a compound microscope ?
Why does the objective lens of an astronomical telescope have a large light gathering power?
Which of the two, objective or eye-piece, of a telescope has a large aperture? Give reason for your answer.
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 ?
Where should an object be placed in front of a convex lens so as to use it as a simple microscope?
A person having a myopic eye used the concave lens of focal length 50cm. What is the power of the lens?
A 52-year old near-sighted person wears eye-glass with a power of –5.5 dioptres for distance viewing. His doctor prescribes a correction of +1.5 dioptres in the near-vision section of his bi-focals. This is measured relative to the main part of the lens (i) What is the focal length of his distance-viewing part of the lens? (ii) What is the focal length of the near-vision section of the lens?
What are the common defects of vision that can be corrected by the use of suitable eyeglasses or spectacles?
Which phenomenon of vision is made use of in cinematography? Explain briefly how it is used.
When is a person said to have developed cataract in his eye? How is the vision of a person having cataract restored?
A telescope has an objective of focal length 140.0 cm and an eyepiece of focal length 5.0 cm. Find
(i) the magnification of the telescope for viewing distant objects for normal adjustment
(ii) separation between the objective lens and the eyepiece.
A person needs a lens of power – 4.5 D for correction of her vision.
(a) What kind of defect in vision is she suffering from?
(b) What is the focal length of the corrective lens?
(c) What is the nature of the corrective lens?
How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.
A compound microscope has an objective of focal length 1.0 cm and an eyepiece of focal length 4.0 cm. If the length of the tube is 20 cm, find the magnification of the compound microscope.