Ray Optics and Optical Test

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Ray Optics and Optical Test - 33

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Weekly Quiz Competition

Question 1
1 / -0

Twinkling of stars is due to

A
variation of refractive index in the earth's atmosphere

B
the fact that light is not emitted by the stars continuously

C
the absorption oflight by earth's atmosphere

D
none of these

Solution

The twinkling of stars is due to atmospheric refraction of star-light. The refraction of light caused by the earth's atmosphere having air layers of varying optical density is called atmospheric refraction.
The physical conditions of the atmosphere keep on changing continuously due to which density of air in different layers of atmosphere also keeps on changing.
As a result of this, the refractive index of the various layers of atmosphere also keeps on changing continuously. So, light coming from stars suffers multiple refraction and the amount of starlight reaching the eye also keeps changing and so, due to fluctuation of perceived brightness of the star, they appear like they are twinkling.

Hence, the correct answer is OPTION A.
Question 2
1 / -0

Twinkling of stars is on account of

A
Large distance of stars and storms in air

B
Small size of stars

C
Large size of stars

D
Large distance of stars and fluctuations in the density of air

Solution

Answer:− D
In simple terms, the twinkling of stars is caused by the passing of light through different layers of a turbulent atmosphere. Twinkling effects are caused by anomalous refraction caused by small-scale fluctuations in air density usually related to temperature gradients
Question 3
1 / -0

The sky is blue because

A
There is more blue light in the sunlight

B
Of scattering of sunlight by air molecules in the atmosphere

C
Of scattering of sunlight by dust particles in the atmosphere

D
Other colours are absorbed by heavenly bodies

Solution

When a parallel beam of light passes through any medium full of molecules and other particles, light gets scattered in every possible direction due to presence of such molecules, dust particles etc.
Also,
Probability of scattering is proportional to $$\dfrac{1}{\lambda^4}$$
therefore, blue scatters more as it has smaller wavelength.
Question 4
1 / -0

The relation between $$u, v$$ ( u is the object distance and v is the image distance ) and f for mirror is given by:

A
$$\displaystyle f=\frac{uv}{u-v}$$

B
$$\displaystyle f=\frac{2u\times v}{u+v}$$

C
$$\displaystyle f=\frac{u\times v}{u+v}$$

D
none of these

Solution

$$\dfrac{1}{u} +\dfrac{1}{v} = \dfrac{1}{f} $$
or $$\dfrac{u+v}{uv} = \dfrac{1}{f}$$
or $$f=\dfrac{uv}{u+v}$$
Question 5
1 / -0

The bending of light ray after passing through a medium is commonly known as :

A
Refraction

B
Scattering

C
Reflection

D
Interference

Solution

Refraction is defined as the phenomenon of bending of light ray when it travels from one medium to another of difefrent refractive index.
Question 6
1 / -0

Choose the correct relation between u, v and r for a spherical mirror:

A
$$\displaystyle r=\frac{2uv}{u+v}$$

B
$$\displaystyle r=\frac{2}{u+v}$$

C
$$\displaystyle r=\frac{2(u+v)}{(uv)}$$

D
$$\displaystyle r=\frac{uv}{u+v}$$

Solution

For a spherical mirror,
$$u $$ is distance of object from pole,
$$v$$ is distance of image from pole.
$$f$$ is focal length of mirror.
From mirror formula
$$\dfrac{1}{v}+\dfrac{1}{u}=\dfrac{1}{f}$$
$$\dfrac{u+v}{uv}=\dfrac{1}{f}$$
So, $$f=\dfrac{uv}{u+v}$$
and since $$r=2f=\dfrac{2uv}{u+v}$$
Question 7
1 / -0

A convex lens magnifying glass is of-

A
Long focal length

B
Short focal length

C
Very long focal length

D
All the above

Solution

A shorter focal length gives better magnification, which is usually the most important thing.
In telescopes, the objective lens projects an image on its focal point which works as the object for the eyepiece. Per the property of convex lenses, the eyepiece magnifies the image. If the focal length of the eyepiece is smaller we'll get a higher magnification.
Question 8
1 / -0

A lean boy named Ramesh placed a glass slab of refractive index $$\dfrac{3}{2}$$ on his photograph. He felt it more interesting as his face appeared bigger than the original size when observed from the top of the glass slab. He also observed that the photo appears at a height of $$1.5$$ cm from the bottom. He then placed another glass cube made of different material and having the same thickness over the first glass cube. Now, he himself started to laugh by seeing his photograph as it appeared still bigger than the previous. When observed from the top the photograph appears to be at a height of $$4$$ cm from the bottom. Determine the refractive index of the second glass cube.

A
$$1.5$$

B
$$2.25$$

C
$$3.75$$

D
$$1.75$$

Solution

The vertical shift due to refractive index variation is given by
$$\delta=t(\mu-1)$$
here t is thickness of medium
$$\mu$$ is refractive index of medium.
and for this question it is given
$$\delta_{1}=1.5cm$$ $$\mu_{1}=\dfrac{3}{2}$$
$$\delta_{2}=4cm$$ for $$\mu_{2}=8$$
so
$$\dfrac{\delta_{1}}{\delta_{2}}=\dfrac{t(\mu_{1}-1)}{t(\mu_{2}-2)}$$
$$\dfrac{1.5}{4}=\dfrac{\dfrac{3}{2}-1}{\mu_{2}-1}$$
$$\dfrac{3}{8}=\dfrac{1}{2(\mu_{2}-1)}$$
$$\mu_{2}-1=\dfrac{4}{3}$$
$$\mu_{2}=\dfrac{7}{3}$$
Question 9
1 / -0

A vessel of water is $$2 m$$ deep. How deep will it appear if looked vertically downward?

$$\displaystyle \left [ _{a}{\mu }_{w} = \frac {4}{3} \right ]$$

A
$$1.5 m$$

B
$$2 m$$

C
$$4 m$$

D
$$1 m$$

Solution

Real depthof water is 2m (given)
Since we know that
$$\mu=\dfrac{real depth}{apparent depth}$$
Hence $$apparent depth=\dfrac{real depth}{\mu}$$
$$=\dfrac{2}{\dfrac{4}{3}}$$
$$apparent depth=1.5 m$$
Question 10
1 / -0

The middle point of a spherical mirror is called

A
pole

B
centre of sphere

C
centre of curvature

D
none of these

Solution

The centre of the reflecting surface of a spherical mirror is a point called the pole. It lies on the surface of the spherical mirror.

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Re-Attempt Weekly Quiz Competition

Ray Optics and Optical Test - 33

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Ray Optics and Optical Test - 33

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SHARING IS CARING

Question 1

variation of refractive index in the earth's atmosphere

the fact that light is not emitted by the stars continuously

the absorption oflight by earth's atmosphere

none of these

Solution

Question 2

Large distance of stars and storms in air

Small size of stars

Large size of stars

Large distance of stars and fluctuations in the density of air

Solution

Question 3

There is more blue light in the sunlight

Of scattering of sunlight by air molecules in the atmosphere

Of scattering of sunlight by dust particles in the atmosphere

Other colours are absorbed by heavenly bodies

Solution

Question 4

$$\displaystyle f=\frac{uv}{u-v}$$

$$\displaystyle f=\frac{2u\times v}{u+v}$$

$$\displaystyle f=\frac{u\times v}{u+v}$$

none of these

Solution

Question 5

Refraction

Scattering

Reflection

Interference

Solution

Question 6

$$\displaystyle r=\frac{2uv}{u+v}$$

$$\displaystyle r=\frac{2}{u+v}$$

$$\displaystyle r=\frac{2(u+v)}{(uv)}$$

$$\displaystyle r=\frac{uv}{u+v}$$

Solution

Question 7

Long focal length

Short focal length

Very long focal length

All the above

Solution

Question 8

$$1.5$$

$$2.25$$

$$3.75$$

$$1.75$$

Solution

Question 9

$$1.5 m$$

$$2 m$$

$$4 m$$

$$1 m$$

Solution

Question 10

pole

centre of sphere

centre of curvature

none of these

Solution

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