Physics

The Human Eye and The Colourful World

Question:

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

Answer:

To achieve a larger magnification of a small object, both the objective and the eyepiece of a compound microscope should have smaller focal lengths. Magnification of the order of 1000 is possible with very good design of the microscopes, such as in the oil-immersion type of microscopes.

previuos
next

The Human Eye and The Colourful World

Q 1.

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

Q 2.

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

Q 3.

How is the terrestrial telescope different from the astronomical telescope?

Q 4.

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

Q 5.

Why do stars twinkle?

Q 6.

What is meant by power of accommodation of the eye?

Q 7.

What are coaxial lenses and where are they used?

Q 8.

Write the names of colours got from the word VIBGYOR.

Q 9.

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

Q 10.

Explain presbyopia and astigmatism.

Q 11.

What is Astigmatism?

Q 12.

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

Q 13.

Why is eye lens of telescope smaller than objective lens?

Q 14.

What is dispersion?

Q 15.

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

Q 16.

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

Q 17.

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 18.

Why is the colour of the clear sky blue?

Q 19.

What is short sight? How can it be corrected?

Q 20.

What is visual axis?

Q 21.

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

Q 22.

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

Q 23.

What is optic axis?

Q 24.

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

Q 25.

How does the eye adjust its focal length?

Q 26.

What is spectrum?

Q 27.

Explain the angle of prism.

Q 28.

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 29.

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 30.

What is visual axis?

Q 31.

Define the term “accommodation of the eye”.

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.

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

Q 34.

Explain clearly the working of a human eye?

Q 35.

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

Q 36.

Why do stars twinkle?

Q 37.

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 38.

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 39.

Explain why the planets do not twinkle ?

Q 40.

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

Q 41.

Draw a diagram of a simple microscope.

Q 42.

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

Q 43.

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

Q 44.

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

Q 45.

How do we see colours?

Q 46.

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 47.

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 48.

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 49.

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.

Q 50.

Define “least distance of distinct vision”.