How does an eye focus the objects lying at various distances?
An eye can focus the images of the distant objects as well as that of the nearby objects on its retina by changing the focal length of its lens. The focal length of the eye-lens is changed by the action of the ciliary muscles. The ciliary muscles can change the thickness of the eye-lens and hence its focal length changes the converging power of the eye-lens.
Why does the objective lens of an astronomical telescope have a large light gathering power?
Give the condition required to achieve a larger magnification of a small object by a compound microscope ?
Which of the two, objective or eye-piece, of a telescope has a large aperture? Give reason for your answer.
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?
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?
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?
What are the common defects of vision that can be corrected by the use of suitable eyeglasses or spectacles?
A person uses convex lens spectacles. What vision defect does he have? Draw a diagram
(i) to show the defective eye
(ii) to show the correction with the 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 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?
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
If we need magnification of 375 from a microscope of tube length 15 cm and objective of focal length 0.5 cm, what focal length of eye-piece should we use?
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.
A person needs a lens of power −5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?
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.
Which phenomenon of vision is made use of in cinematography? Explain briefly how it is used.