NCERT Class X Science Class: Chapter –11. Human Eye and Colourful World – Part-5

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Question 16:

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.

Answer:

The student is suffering from myopia (near sightedness). Doctor advises her to use a concave lens of appropriate power to correct this defect.

Image correction for myopia eye

Image Correction for Myopia Eye

Image correction for myopia eye

Question 17:

How are we able to see nearby and also the distant objects clearly?

Answer:

Human eye is able to see nearby and distant objects clearly by changing the focal length of the eye lens using its power of accommodation

Image contracted and relaxed muscle.

Image Contracted and Relaxed Muscle.

Image contracted and relaxed muscle.

Question 18:

A person needs a lens of power 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?

Answer:

(a) Myopia

Image normal vision and myopia

Image Normal Vision and Myopia

Image normal vision and myopia

(b)

(c) Concave lens

Image myopia andcorrection concave lens

Image Myopia Andcorrection Concave Lens

Image myopia andcorrection concave lens

Question 19:

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.

Answer:

By using two identical prisms, one placed inverted with respect to the other we get a narrow beam of white light incident on one prism emerges out of the second prism as white light.

Image two identical prisms

Image Two Identical Prisms

Image two identical prisms

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