Human Eye and Colourful World Test

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Human Eye and Colourful World Test - 51

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Weekly Quiz Competition

Question 1
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To read a poster on a wall, a person with defective vision needs to stand at a distance of $$0.4m$$ from the poster. A person with normal vision can read the poster from a distance of $$2.0m$$. Which one of the following lens may be used to correct the defective vision?

A
A concave lens of $$0.5D$$

B
A concave lens of $$1.0D$$

C
A concave lens of $$2.0D$$

D
A convex lens of $$2.0D$$

Solution

From the given problem, it is clear that the person can not see far objects. Therefore, he is suffering from hypermetropia. This defect can be corrected by using a concave lens of suitable power.

$$\text{Calculating the power of the concave lens:}$$
Given: the object distance $$u=-2m$$
the image distance $$v=-0.4m$$
Using the lens formula,
$$\cfrac { 1 }{ f } =\cfrac { 1 }{ v } -\cfrac { 1 }{ u } $$
$$P=\cfrac { 1 }{ f } =-\cfrac { 1 }{ 0.4 } -\cfrac { 1 }{ (-2) } =-2$$
$$P=-2D$$
The power of the concave lens should be $$2D$$.
Question 2
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Rainbow is produced when sunlight falls on drops of rain, Which of the following physical phenomena are responsible for this?

A
Diffusion

B
Dispersion and total internal reflection

C
Only refraction

D
Diffusion, refraction and total internal reflection
Question 3
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If the power of an eye lens increases, then the defect of vision so produced is known as

A
Colour blindness

B
Long sightedness

C
Short sightedness

D
None of the above

Solution

As the power of the lens increases its focal length will decrease and this happens in short-sightedness.
Question 4
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A mirage is observed when

A
Density of air decreases with increase of height

B
Density of air increases with increase of height

C
Refractive index of air decreases with increase of height

D
The Earth acts like a mirror.

Solution

Mirage is seen in summer because the air near the ground becomes hotter (lower refractive index) than air further up (higher refractive index). Thus a ray of light from an object (tree) gets bent and is totally internally reflected. Observer assumes that it is reflected from ground.
Question 5
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Rainbow is produced when sunlight falls on drops of rain. Which of the following physical phenomena is/are responsible for this?

A
Diffusion

B
Dispersion and refraction

C
Only refraction

D
Refraction, dispersion and total internal reflection.
Solution
Following phenomena take place when sunlight falls on drop of rain:
It undergoes refraction at B and splits into different colours (dispersion).
It is then internally reflected at C and
Refracted again at D while coming out of the drop.
Question 6
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The middle vascular coat that darkens the eye chamber and prevents refraction by absorbing the light rays is

A
Choroid

B
Sclera

C
Retina

D
Cornea.

Solution
Question 7
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The sky appears blue, due

A
To scattering of light by dust particles

B
To the colour of the sea water

C
To the presence of water in clouds

D
None of these

Solution
Question 8
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Which of the following statements is correct about rainbow?

A
In primary rainbow, red colour on the outside and violet colour on the inside.

B
In primary rainbow, violet colour on the outside and red colour on the inside.

C
Secondary rainbow is brighter than primary rainbow.

D
In secondary rainbow, light waves suffers one total internal reflection before coming out.
Question 9
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A normal eye is not table to see objects closer than $$25$$cm because.

A
The focal length of the eye is $$25$$cm

B
The eye is not able to decrease the focal length of eye lens beyond a limit

C
The distance of the retina from the eye lens is $$25$$cm

D
The eye is not able to decrease the distance between the eye lens and the retina beyond a limit

Solution

Focal length of the eye lens is adjusted by changing its radius of curvature. This is performed by the ciliary muscles. Thus it can stretch or contract upto a certain limit only and hence the focal length cannot decrease beyond a limit .
Question 10
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The spread in colours in a rainbow on sky is primarily due to

A
Dispersion of sunlight

B
Reflection of sunlight

C
Refraction of sunlight

D
Total internal reflection of sunlight

Solution

The spread in colours in a rainbow on sky is primarily due to dispersion of sunlight.

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Re-Attempt Weekly Quiz Competition

Human Eye and Colourful World Test - 51

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Human Eye and Colourful World Test - 51

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SHARING IS CARING

Question 1

A concave lens of $$0.5D$$

A concave lens of $$1.0D$$

A concave lens of $$2.0D$$

A convex lens of $$2.0D$$

Solution

Question 2

Diffusion

Dispersion and total internal reflection

Only refraction

Diffusion, refraction and total internal reflection

Question 3

Colour blindness

Long sightedness

Short sightedness

None of the above

Solution

Question 4

Density of air decreases with increase of height

Density of air increases with increase of height

Refractive index of air decreases with increase of height

The Earth acts like a mirror.

Solution

Question 5

Diffusion

Dispersion and refraction

Only refraction

Refraction, dispersion and total internal reflection.

Solution

Question 6

Choroid

Sclera

Retina

Cornea.

Solution

Question 7

To scattering of light by dust particles

To the colour of the sea water

To the presence of water in clouds

None of these

Solution

Question 8

In primary rainbow, red colour on the outside and violet colour on the inside.

In primary rainbow, violet colour on the outside and red colour on the inside.

Secondary rainbow is brighter than primary rainbow.

In secondary rainbow, light waves suffers one total internal reflection before coming out.

Question 9

The focal length of the eye is $$25$$cm

The eye is not able to decrease the focal length of eye lens beyond a limit

The distance of the retina from the eye lens is $$25$$cm

The eye is not able to decrease the distance between the eye lens and the retina beyond a limit

Solution

Question 10

Dispersion of sunlight

Reflection of sunlight

Refraction of sunlight

Total internal reflection of sunlight

Solution

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