Human Eye and Colourful World Science - Human Eye and Colourful World

For the refraction of a ray of light through a glass prism, the path of a ray of light is shown below :
The angle of incidence, the angle of emergence and the angle of deviation respectively have been represented by

The path of a ray of light passing through a glass prism is shown below : In this diagram the angle of prism, angle of incidence, angle of emergence and angle of deviation respectively have been represented by

In the following questions, a statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as :
Assertion : Rainbow is an example of the dispersion of sunlight by the water droplets.
Reason : Light of shorter wavelength is scattered much more than light of larger wavelength.

In the following questions, a statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as :
Assertion : An image formed on retina is real. diminished and inverted in nature.
Reason : The eye lens is convex lens.

To bring light from a distant object to a focus on the retina of the eye, the convex eye-lens needs to be made ____.

The iris controls the amount of _____ entering the eye.

Ability to adjust the focal length is called _______

When light is dim, the pupil becomes _____.

_______ acts as lens in the eye.

State whether the following statements are true or false:

1. The scattering away of red light makes the sky appear blue during the day time.
2. The scattering away of blue light makes the sun appear red at sunset.

State whether the following statement is true or false:
Rabbit has eyes which look sideways.

State whether the following statement is true or false:
The planets twinkle at night due to atmospheric refraction of light.

Scattering of light is inversely proportional to the fourth power of wavelength. [True/ False]

Looming happens due to total internal reflection. [True/ False]

List the factors on which the angle of deviation through a prism depend?

State one function of iris in human eye.

Give an example of a phenomenon where Tyndall effect can be observed.

Name the component of white light that deviates the least and the component that deviates the most while passing through a glass prism.

What will be the observed colour of the sky on a planet where there is no atmosphere? Why?

Draw a labelled ray diagram to illustrate the dispersion of a narrow beam of white light when it passes through glass prism.

Explain with the help of a diagram, how we are able to observe the sunrise about two minutes before the sun gets above the horizon.

Draw a ray diagram to show the refraction of light through a glass prism. Mark on it,

1. The incident ray,
2. The emergent ray,
3. The angle of deviation.

When we place a glass prism in the path of a narrow beam of white light a spectrum is obtained. What happens when a second identical prism is placed in an inverted position with respect to the first prism? Draw a labelled ray diagram to illustrate it.

A star sometimes appears brighter and some other times fainter. What is this effect called? State the reason for this effect.

What is ‘‘dispersion of white light’’? Draw a labelled diagram to illustrate the recombination of the spectrum of white light. Why is it essential that the two prisms used for the purpose should be identical and placed in an inverted position with respect to each other?

With the help of scattering of light, explain the reason for the difference in colours of the sun as it appears during sunrise/ sunset and noon.

What is ‘dispersion of white light’? State its cause. Draw a ray diagram to show the dispersion of white light by a glass prism.

State the cause of dispersion of white light by a glass prism. How did Newton, using two identical glass prisms, show that white light is made of seven colours ? Draw a ray diagram to show the path of a narrow beam of white light, through a combination of two identical prisms arranged together in inverted position with respect to each other, when it is allowed to fall obliquely on one of the faces of the first prism of the combination.

What is meant by scattering of light? Use this phenomenon to explain why the clear sky appears blue or the sun appears reddish at sunrise.

1. List the parts of the human eye that control the amount of light entering into it. Explain how they perform this function.
2. Write the function of retina in human eye.
3. Do you know that the corneal-impairment can be cured by replacing the defective cornea with the cornea of the donated eye? How and why should we organise groups to motivate the community members to donate their eyes after death?

What is atmospheric refraction? Use this phenomenon to explain the following natural events.

1. Twinkling of stars.
2. Advanced sun-rise and delayed sun-set.

Draw diagrams to illustrate your answers.

Write the importance of ciliary muscles in the human eye. Name the defect of vision that arises due to gradual weakening of the ciliary muscles in old age. What type of lenses are required by the persons suffering from this defect to see the objects clearly?
Akshay, sitting in the last row in his class, could not see clearly the words written on the blackboard. When the teacher noticed it, he announced if any student sitting in the front row could volunteer to exchange his seat with Akshay. Salman immediately agreed to exchange his seat with Akshay. He could now see the words written on the blackboard clearly. The teacher thought it fit to send the message to Akshay’s parents advising them to get his eyesight checked.
In the context of the above event, answer the following questions:

1. Which defect of vision is Akshay suffering from? Which type of lens is used to correct this defect?
2. State the values displayed by the teacher and Salman.
3. In your opinion, in what way can Akshay express his gratitude towards the teacher and Salman?

1. A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain.

1. Why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.
2. The type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.

2. If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention.

1. A student cannot see clearly a chart hanging on a wall placed at a distance of 3 m from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes.
2. Draw a ray diagram to show how this defect may be corrected using a lens of apropriate focal length.
3. An eye donation camp is being organised by social workers in your locality. How and why would you help in this cause?

The human eye is like a camera. Its lens system forms an image on a light-sensitive screen called the retina. Light enters the eye through a thin membrane called the cornea. It forms the transparent bulge on the front surface of the eyeball as shown in the figure. The crystalline lens merely provides the finer adjustment of focal length required to focus objects at different distances on the retina. We find a structure called iris behind the cornea. Iris is a dark muscular diaphragm that controls the size of the pupil. The pupil regulates and controls the amount of light entering the eye.

There are mainly three common refractive defects of vision. These are (i) myopia or near-sightedness, (ii) hypermetropia or far-sightedness, and (iii) Presbyopia. These defects can be corrected by the use of suitable spherical lenses.
(i) What is the function of pupil in the human eye ?
(ii) What is the far point and near point of human eye with normal vision?
(iii) A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from?
(iv) What is the function of iris in human eye ?