Ray Optics and Optical Test

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Ray Optics and Optical Test - 12

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Weekly Quiz Competition

Question 1
1 / -0

When Astronauts fly at higher altitude, the sky appears dark because ;

A
Scattering of light does not take place.

B
Scattering of light takes place.

C
Refraction of light takes place.

D
Dispersion of light takes place.

Solution

When sunlight passes through the atmosphere, the fine particles in the air scatter the blue color (shorter wavelengths) more strongly than red. The scattered blue light enters our eyes.
When Astronauts fly at higher altitudes, the sky appears dark because, at very high altitudes, there is no atmosphere. So, there would not have been any scattering of light.
Question 2
1 / -0

Two light rays $$P$$ and $$Q$$ are incident an optical device $$'X'$$ which finally goes along $$'R'$$ and $$'S'$$. Identify optical device $$'X'$$.

A
Concave lens

B
Concave mirror

C
Convex lens

D
Convex mirror

Solution

Since in convex mirror, a ray travelling parallel to the principal axis virtually emanates from the virtual focal point after reflection by the mirror.
Hence, optical device would be convex mirror i.e., option (d)
Question 3
1 / -0

The focal length of a lens of refractive index $$\mu $$ is $$f$$. If the lens is immersed in a liquid of refractive index $$\mu $$ then the focal length of lens is

A
$$\dfrac{f}{2}$$

B
$$2f$$

C
$$\text{infinite}$$

D
$$\text{zero}$$

Solution

$$\dfrac{1}{f} = (n-1) (\dfrac{1}{R_1}- \dfrac{1}{R_2})$$
where, $$n$$ is refractive index of lens material with respect to its surrounding medium
If lens is immersed in the liquid of refractive index equal to its own then $$n=1$$ and hence above equation becomes: $$\dfrac{1}{f} = 0$$
$$\Rightarrow f = \infty$$
Question 4
1 / -0

A convex glass lens is immersed in water. Compared to the power in air, its power in water will :

A
increase

B
decrease

C
not change

D
decrease for red light and increase for violet light

Solution

Power of a lens $$=\dfrac{1}{f}$$
Where $$f $$ is the focal length of the lens.
So, by lens maker formula
$$\dfrac{1}{f}=\left ( \dfrac{\mu _{2}}{\mu _{1}}-1 \right )\left ( \dfrac{1}{R_{1}}-\dfrac{1}{R_{2}} \right )$$
As lens is dipped in water, $$\mu$$ of the medium is increased from 1 to $$\dfrac{4}{3} $$ (i.e. refractive index of water), so, $$\dfrac{\mu_{2}}{\mu_{1}}$$ term decreases, so, $$\left ( \dfrac{\mu_{2}}{\mu_{1}}-1 \right )$$ term decrease which leads to decrease of $$\dfrac{1}{f}.$$ so, power $$\left ( =\dfrac{1}{f} \right )$$ decreases.
Question 5
1 / -0

A glass slab is placed in the path of beam of convergent light. The point of convergence of light

A
moves towards the glass slab

B
moves away from the glass slab

C
remains at the same point

D
undergoes a lateral shift

Solution

As a glass has refractive index of 3/2 with respect to air, the convergent light will bend towards the normal in the glass and again bend away from the normal, but in the whole process the beam is displaced parallel to initial path as shown in figure and converge at a greater distance from the glass slab.
Question 6
1 / -0

What are the colours of the Sun observed most during sunrise/sunset and noon?

A
white and red

B
reddish and orange

C
yellow and reddish

D
orange and blue

Solution

During sunrise and sunset the sun rays have to pass through a larger distance and also a greater thickness of air since it is low in the sky. At these positions, the sky looks orange-red colour because photons of red and orange light are least scattered through the atmosphere and are able to reach our eyes.
Question 7
1 / -0

Red light is used as danger signal because it is:

A
Accepted as symbol

B
Pleasing to the eye

C
Sensitive to the eye

D
Has high wavelength

Solution

Red light is used as danger signal because it is having high wavelength, less scattering ,hence can travel larger distances.
Question 8
1 / -0

The line joining the pole and the centre of curvature of a mirror is called the :

A
Aperture

B
Principal section

C
Principal axis

D
Pole

Solution

The line joining the pole and the center of curvature of a mirror is called the principal axis.
Question 9
1 / -0

The relation between u, v and r is:

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

B
$$r=\dfrac {2}{u+v}$$

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

D
None of these

Solution

We know,
$$ 1/f = 1/u +1/v$$
Or $$2/r = 1/u +1/v$$
Since radius of curvature is double the focal length. This leads to option A.
Question 10
1 / -0

An achromatic combination of lenses produce :

A
images in black and white

B
colored images

C
images unaffected by variation of refractive index with wavelength

D
highly enlarged images

Solution

An achromatic combination of lenses provide deviation without dispersion. So, images are unaffected by variation of refractive index with wavelength. Hence correct option is C.

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Ray Optics and Optical Test - 12

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Ray Optics and Optical Test - 12

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Question 1

Scattering of light does not take place.

Scattering of light takes place.

Refraction of light takes place.

Dispersion of light takes place.

Solution

Question 2

Concave lens

Concave mirror

Convex lens

Convex mirror

Solution

Question 3

$$\dfrac{f}{2}$$

$$2f$$

$$\text{infinite}$$

$$\text{zero}$$

Solution

Question 4

increase

decrease

not change

decrease for red light and increase for violet light

Solution

Question 5

moves towards the glass slab

moves away from the glass slab

remains at the same point

undergoes a lateral shift

Solution

Question 6

white and red

reddish and orange

yellow and reddish

orange and blue

Solution

Question 7

Accepted as symbol

Pleasing to the eye

Sensitive to the eye

Has high wavelength

Solution

Question 8

Aperture

Principal section

Principal axis

Pole

Solution

Question 9

$$r=\dfrac {2uv}{u+v}$$

$$r=\dfrac {2}{u+v}$$

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

None of these

Solution

Question 10

images in black and white

colored images

images unaffected by variation of refractive index with wavelength

highly enlarged images

Solution

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