Physics

The Human Eye and The Colourful World

Question:

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.

Answer:

Focal length of objective fo = 10 cm
Focal length of eyepiece fe = 4 cm
(i) In normal adjustment
Extra-Questions-for-class-10-Science- Human-Eye-and-Colourful-World-Q19

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The Human Eye and The Colourful World

Q 1.

What is dispersion?

Q 2.

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

Q 3.

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 4.

How does the eye adjust its focal length?

Q 5.

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

Q 6.

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

Q 7.

What is meant by power of accommodation of the eye?

Q 8.

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

Q 9.

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

Q 10.

What is visual axis?

Q 11.

What is short sight? How can it be corrected?

Q 12.

Where should an object be placed in front of a convex lens so as to use it as a simple microscope?

Q 13.

Write the names of colours got from the word VIBGYOR.

Q 14.

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 15.

Explain why the planets do not twinkle ?

Q 16.

Why do stars twinkle?

Q 17.

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 18.

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

Q 19.

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

Q 20.

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

Q 21.

Why do stars twinkle?

Q 22.

How is the terrestrial telescope different from the astronomical telescope?

Q 23.

What is optic axis?

Q 24.

Explain clearly the working of a human eye?

Q 25.

Explain presbyopia and astigmatism.

Q 26.

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

Q 27.

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 28.

Why is the colour of the clear sky blue?

Q 29.

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

Q 30.

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

Q 31.

Why does the sun appear reddish early in the morning?

Q 32.

Define the term “accommodation of the eye”.

Q 33.

What is spectrum?

Q 34.

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

Q 35.

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.

Q 36.

When is a person said to have developed cataract in his eye? How is the vision of a person having cataract restored?

Q 37.

What is Astigmatism?

Q 38.

What is visual axis?

Q 39.

Define “least distance of distinct vision”.

Q 40.

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 41.

Draw a diagram of a simple microscope.

Q 42.

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 43.

How do we see colours?

Q 44.

Why is the colour of the clear sky blue?

Q 45.

How are we able to see nearby as well as the distant objects clearly?

Q 46.

Why is eye lens of telescope smaller than objective lens?

Q 47.

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

Q 48.

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 49.

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

Q 50.

What are coaxial lenses and where are they used?