physics - the human eye and the colourful world

Class 10 - Physics

The Human Eye and The Colourful World

Q&A
Question:

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

Answer:

Persistence of vision is made use of in cinematography. It is the ability of an eye to continue to see the image of an object for a very short duration even after the removal of the object. We are able to see the movie pictures in a cinema due to the persistence of vision.
The still pictures taken by a movie camera are projected on the screen at a rate of about 24 pictures per second. Under these conditions, the image of one picture persists on the retina till the image of next picture falls on the screen and so on.
Due to this, the slightly different images of the successive pictures present on the film merge smoothly into one another and give us the feeling of moving images. Thus the principle of persistence of vision is made use of, in the motion picture projection in cinematography.



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Questions and Answers


The Human Eye and The Colourful World - Questions
1.

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


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2.

What is optic axis?


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3.

What is visual axis?


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4.

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.


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5.

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


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6.

How do we see colours?


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7.

Draw a diagram of a simple microscope.


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8.

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.


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9.

How is the terrestrial telescope different from the astronomical telescope?


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10.

What is dispersion?


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11.

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


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12.

Why do stars twinkle?


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13.

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


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14.

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


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15.

What is Astigmatism?


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16.

What is phorias?


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17.

When do we consider a person to be myopic or hypermetropic? Explain using diagrams how the defects associated with myopic and hypermetropic eye can be corrected?


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18.

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


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19.

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


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20.

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


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21.

What is spectrum?


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22.

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 ?


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23.

Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye ¡s 1 m. What ¡s the power of a lens required to correct this defect? Assume that near point of the normal eye is 25 cm.


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24.

Why does the sun appear reddish early in the morning?


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25.

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


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26.

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


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27.

Explain clearly the working of a human eye?


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28.

What are coaxial lenses and where are they used?


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29.

Explain presbyopia and astigmatism.


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30.

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.


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31.

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.


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32.

Explain the angle of prism.


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33.

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.


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34.

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


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35.

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?


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36.

Why do stars twinkle?


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37.

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


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38.

What is short sight? How can it be corrected?


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39.

Define “least distance of distinct vision”.


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40.

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


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41.

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


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42.

Write the names of colours got from the word VIBGYOR.


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43.

Why is eye lens of telescope smaller than objective lens?


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44.

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


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45.

What is visual axis?


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46.

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


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47.

Define the term “accommodation of the eye”.


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48.

How does the eye adjust its focal length?


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49.

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?


Answer
50.

Explain the structure and functioning of Human eye. How are we able to see nearby as well as distant objects?


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