Physics

The Human Eye and The Colourful World

Question:

Explain why the planets do not twinkle ?

Answer:

Planets being close to earth appear larger in size. A planet can be Considered as a collection of large number of small sized objects. Twinkling effect Of these objects cancel each other. so, planets do not appear to twinkle.

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The Human Eye and The Colourful World

Q 1.

How is the terrestrial telescope different from the astronomical telescope?

Q 2.

Which of the two, objective or eye-piece, of a telescope has a large aperture? Give reason for your answer.

Q 3.

How does the eye adjust its focal length?

Q 4.

Differentiate between a microscope and a telescope based on its use.

Q 5.

What is visual axis?

Q 6.

Why do stars twinkle?

Q 7.

Write the names of colours got from the word VIBGYOR.

Q 8.

What is meant by power of accommodation of the eye?

Q 9.

Give the condition required to achieve a larger magnification of a small object by a compound microscope ?

Q 10.

Why does the objective lens of an astronomical telescope have a large light gathering power?

Q 11.

What are coaxial lenses and where are they used?

Q 12.

What is Astigmatism?

Q 13.

Explain presbyopia and astigmatism.

Q 14.

What is visual axis?

Q 15.

How does the eye adjust itself to deal with light of varying intensity?

Q 16.

Is the position of a star as seen by us its true position? Justify your answer.

Q 17.

What is dispersion?

Q 18.

Which part of human eye helps in the perception of colours?

Q 19.

What are the common defects of vision that can be corrected by the use of suitable eyeglasses or spectacles?

Q 20.

Why is the colour of the clear sky blue?

Q 21.

What is short sight? How can it be corrected?

Q 22.

What is spectrum?

Q 23.

What property of the eye is the principle of motion, pictures?

Q 24.

Why is eye lens of telescope smaller than objective lens?

Q 25.

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?

Q 26.

Explain clearly the working of a human eye?

Q 27.

Which phenomenon of vision is made use of in cinematography? Explain briefly how it is used.

Q 28.

Define the term “accommodation of the eye”.

Q 29.

A lens used as a simple magnifier gives magnification of 6. What is its focal length?

Q 30.

Explain the angle of prism.

Q 31.

What is the far point and near point of the human eye with normal vision ?

Q 32.

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?

Q 33.

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?

Q 34.

What is optic axis?

Q 35.

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 ?

Q 36.

How does an eye focus the objects lying at various distances?

Q 37.

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?

Q 38.

Draw a diagram of a simple microscope.

Q 39.

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.

Q 40.

Explain why the planets do not twinkle ?

Q 41.

Why do stars twinkle?

Q 42.

A person having a myopic eye used the concave lens of focal length 50cm. What is the power of the lens?

Q 43.

Why does the sky appear dark of blue to an astronaut?

Q 44.

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?

Q 45.

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.

Q 46.

Why does the sun appear reddish early in the morning?

Q 47.

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.

Q 48.

Define “least distance of distinct vision”.

Q 49.

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.

Q 50.

How will you distinguish between a compound microscope and a telescope.