Ray Optics and Optical Test

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Ray Optics and Optical Test - 30

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Weekly Quiz Competition

Question 1
1 / -0

Consider the following statements:
(a) Real image is always inverted
(b) Virtual image is always erect
(c) Image formed by a concave lens is always real and inverted.
Which of the above statement(s) is/are correct?

A
Only (a)

B
Only (b)

C
(a) and (b)

D
All of the above

Solution
Question 2
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In a spherical mirror, normal drawn on any point on a spherical mirror passes through :

A
Focus

B
Pole of the mirror

C
Centre of curvature

D
None of the above

Solution

In a spherical mirror, normal drawn on any point on a spherical mirror passes through the centre of curvature.
Question 3
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Why does a straight rod appear bent in water?

A
Due to reflection of light

B
Due to refraction of light

C
Due to variable refractive index of water

D
None of the above

Solution

This phenomenon occurs due to the property of light called refraction of light. When a stick is immersed in water, in actually we are putting it from rarer medium to denser medium. So, when the rays of light pass from a rarer medium to the denser medium they move towards the normal, the part of stick immersed in water appears to bend when immersed in water and this refraction causes an apparent shift in the position of the part of the rod within the water.
Question 4
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Consider the following statements:
(a) Light bends from its path, when it goes from one medium to another medium
(b) Speed of light changes, when it goes from one medium to another medium
(c) Wavelength of light decreases, when it travels from air to water
(d) Wavelength of light in water $$=\displaystyle\frac{Wavelength of light in air}{Refractive index of water}$$
Which of the above statements are correct?

A
(b) and (c)

B
(a) and (b)

C
(a), (b) and (d)

D
(a), (b), (c) and (d)

Solution

When a ray of light goes from one medium to another medium it bends from its path. This phenomenon is called refraction of light.
Refractive index of a medium $$\mu =\displaystyle\frac{Velocity of light in vacuum / air}{Velocity of light in medium}$$
Velocity $$V = fl$$
Question 5
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Blue colour of sky is due to :

A
dispersion of light

B
scattering of light

C
reflection of light

D
refraction of light

Solution

Hint:
Rayleigh Scattering Theory suggests that scattering of light is inversely proportional to fourth power of wavelength of light.

Correct Option is B.
Explanation for the correct answer:
$$\bullet$$ Dispersion of Light is a phenomenon in which white light is dispersed into seven colors, when passed through a glass prism. This phenomenon is the reason for formation of rainbow, not for blue color of sky. Option A is incorrect.
$$\bullet$$ Scattering of light is the phenomenon in which path of light gets deviated by striking and obstacle like dust particles. The particles present in our atmosphere are of very small size. Thus, they can deviate only that part of light whose wavelength is closer to their size.
$$\bullet$$ White light coming from Sun is made up of seven colors. Wavelength of Red color is the largest and that of violet and blue is the smallest. Thus, the violet and blue color are scattered most by these particles, thus the sky appears to be blue. Option B is correct.
$$\bullet$$ Reflection of light is the phenomenon in which light bounces back after striking a surface. And retraction of light is bend in path of light when it the medium of its propagation changes. They are not responsible for blue color of light Option C and D are incorrect.

Thus, only Option B is correct.
Question 6
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Which of the following (referred to as spherical mirror) depends on whether the rays are paraxial or not?

A
Pole

B
Focus

C
Radius of curvature

D
Principal axis

Solution

The pole, the radius of curvature, and the principal axis are the geometric nomenclatures of points and axis respectively.
However focus is the only point where a parallel beam of light concentrates after reflection, which depends upon the nature of rays.
Question 7
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A spectrum is obtained by sending a beam of white light through a prism. A second prism exactly similar to the first one is placed in an inverted position with the sides parallel to the first. Now

A
A new spectrum will be formed on the screen with double the number of colours present in the previous spectrum

B
New spectrum will be obtained on the screen with only half the number of colours present in the previous spectrum

C
Previous spectrum will disappear and we will obtain a white light formed by the fusion of the colours

D
A spectrum with same number of colours present in the previous spectrum will be formed but their wave lengths will be increased twice

Solution

A spectrum is obtained by sending a beam of white light through a prism. A second prism exactly similar to the first one is placed in an inverted position with the sides parallel to the first. Now the previous spectrum will disappear and we will obtain a white light formed by the fusion of the colours.
As white is composed of seven colors. The seven colors together joins to form white light again.
Question 8
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.......... happens when a wave passes from one medium to another at an angle.

A
Refraction

B
Reflection

C
Dispersion

D
Scattering

Solution

Refraction is a phenomenon in which when a ray passes from one medium to another it bends away from its straight-line path due to the difference in optical densities or refractive indices of the two mediums.
Option A is correct.
Question 9
1 / -0

A coin kept in a container and not visible can be viewed by pouring water into the container. It happens because of the

A
Reflection of light.

B
Refraction of light.

C
Variable refractive index of water.

D
None of the above.

Solution

When water is poured then it is due to refraction of light the coin becomes visible. When the light rays travel from the water medium (denser) to the air medium (rarer) it bends away from the normal due to the refraction. Therefore, an image of the coin is formed at a smaller depth causing it to be visible (as shown in the figure).
Question 10
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The angle between the normal and refracted ray is called :

A
angle of deviation

B
angle of incidence

C
angle of refraction

D
none of these

Solution

Correct answer is (c)

The angle formed between the normal and refracted ray at the point of refraction is called angle of refraction.