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.
Objective of focal length, f0 = 140.0 cm.
Eyepiece if focal length, fe = 5.0 cm.
How is the terrestrial telescope different from the astronomical telescope?
Write the names of colours got from the word VIBGYOR.
What is visual axis?
Differentiate between a microscope and a telescope based on its use.
What is meant by power of accommodation of the eye?
Which of the two, objective or eye-piece, of a telescope has a large aperture? Give reason for your answer.
How does the eye adjust its focal length?
Why do stars twinkle?
Why does the objective lens of an astronomical telescope have a large light gathering power?
What are coaxial lenses and where are they used?
What is Astigmatism?
Is the position of a star as seen by us its true position? Justify your answer.
Explain presbyopia and astigmatism.
What is dispersion?
Which part of human eye helps in the perception of colours?
How does the eye adjust itself to deal with light of varying intensity?
What are the common defects of vision that can be corrected by the use of suitable eyeglasses or spectacles?
What is short sight? How can it be corrected?
What is spectrum?
What is visual axis?
Why is the colour of the clear sky blue?
Give the condition required to achieve a larger magnification of a small object by a compound microscope ?
Why is eye lens of telescope smaller than objective 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 property of the eye is the principle of motion, pictures?
Explain clearly the working of a human eye?
Which phenomenon of vision is made use of in cinematography? Explain briefly how it is used.
A person needs a lens of power âˆ’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?
What is optic axis?
A 52-year old near-sighted person wears eye-glass with a power of â€“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?
A lens used as a simple magnifier gives magnification of 6. What is its focal length?
What is the far point and near point of the human eye with normal vision ?
Define the term “accommodation of the eye”.
How does an eye focus the objects lying at various distances?
Explain the angle of prism.
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 ?
Draw a diagram of a simple microscope.
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?
Why does the sky appear dark of blue to an astronaut?
A person having a myopic eye used the concave lens of focal length 50cm. What is the power of the lens?
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?
Why do stars twinkle?
Explain why the planets do not twinkle ?
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.
Why does the sun appear reddish early in the morning?
Define “least distance of distinct 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.
If focal length of the objective and eye-piece of a telescope are 10 cm and 4 cm respectively, what will be its magnifying power in
(i) normal adjustments,
(ii) adjustment where image of distance object is formed at D? Given D = 25 cm.
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?
How do we see colours?