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Example questions from human eye and colourful world

 HUMAN EYE AND COLOURFUL WORLD

EXAMPLE QUESTIONS:

 

1  1) Light of wavelength λ1 enters a medium with refractive index n2 from a medium with refractive index n1. What is the wavelength of light in second medium?

ANS:  we know, refractive index is inversely proportional to wavelength.

            n∞1/ λ

ð n1/n2= λ2/ λ1

ð λ2=n1 λ1/n2

 

2  2)  If a white sheet of paper is stained with oil, the paper turns transparent. Why?


ANS: we can get so many answers for this question because there may be multiple reasons for this. But i will suggest one best answer for this.

A white sheet of paper consists of cellulose. The refractive index of cellulose is very near to the refractive index of oil. so, it turns transparent.

 

3    3) A light ray falls on one of the faces of a prism at an angle 40o so that it suffers angle of minimum deviation of 30o. Find the angle of prism and angle of refraction at the given surface.


ANS: To answer this question i suggest you to revise the derivation part of finding refractive index of prism.

Given i1=400

            D=300

At minimum deviation i1=i2=i  and r1=r2=r

ð A+D=2i

ð A=2i-D

ð A=2(40)-30

ð A=500  (angle of prism)

Also we know, d= (i1+i2)-(r1+r2)

ð D=2i-2r  (at minimum deviation)

ð 2r=2i-D

ð r=[2i-D]/2

ð r=[2(40)-30]/2

ð r=50/2=250

 

4)     4) The focal length of a lens suggested to a person with Hypermetropia is 100 cm. Find the distance of near point and power of the lens.

ANS:

      Given f=100 cm

We know focal length of hypermetropia is given by

f=25d/(d-25), where d is the near point.

ð 100=25d/(d-25)

ð 100d-2500=25d

ð 75d=2500

ð d=2500/75=33.33 cm

 

5    5) A student sitting in last bench of a class room cannot see the black board clearly. What is the name of the eye defect he has? What lens is suggested for this defect?


ANS: As the student cannot see far objects he has the defect of short sightedness which is known as myopia. To correct this defect a bi concave lens is suggested.

 

6   6) A person in a car cannot see objects in the rear view mirror of the car. What is the name of the eye defect he has? What lens is suggested for this defect?


ANS: As the person cannot see near objects, he is suffering from far sightedness which is known as hypermetropia. A bi convex lens is used to correct this defect.

7)7)    What type of lens is suggested for the people suffering from presbiopia?

Draw the symbol of this lens.

ANS: For the people suffering from presbiopia a ‘bi focal lens’ is suggested. It is represented symbolically as 

Bifocal lens symbol

The upper portion is concave and the lower portion is convex.



thank you

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