Ray Optics and Optical Test

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Ray Optics and Optical Test - 29

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Weekly Quiz Competition

Question 1
1 / -0

The centre of curvature of a concave mirror :

A
lies in front of it

B
lies behind it

C
lies on the surface of mirror

D
none of these

Solution

From the attached figure, it can be observed that the centre of curvature C lies in front of the concave mirror.
Question 2
1 / -0

A magnifying glass forms:

A
a real and diminished image

B
a real and magnified image

C
a virtual and magnified image

D
a virtual and diminished image.

Solution

A magnifying glass is a convex lens which produces a magnified (larger) image of an object.
A magnifying glass produces an upright, magnified virtual image. The virtual image produced is on the same side of the lens as the object. For a magnified image to be observed the distance between the object and the lens must be shorter than the focal length of the lens.
Hence, a magnifying glass produces a virtual and magnified image.
Question 3
1 / -0

A water pond appears to be $$2.7$$ in deep. If the refractive index of water is $$4/3$$, find the actual depth of the pond.

A
$$2.7 \ m$$

B
$$0.9 \ m$$

C
$$3.6 \ m$$

D
$$1.8 \ m$$

Solution

$$RI=\dfrac{\text{real depth}}{\text{apparent depth}}$$

Substituting, $$\dfrac{4}{3}=\dfrac{real \ depth}{2.7}$$

Therefore, $$real \ depth=\dfrac{2.7\times4}{3}=3.6$$

$$Real \ depth = 3.6 m$$
Question 4
1 / -0

What characteristic property of light is responsible for the blue colour of the sky?

A
Interference

B
Diffraction

C
Scattering

D
Dispersion

Solution

A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colors because the blue light has been scattered out and away from the line of sight.
Hence, scattering is the characteristic property of light which is responsible for the blue colour of the sky.
Question 5
1 / -0

An astronaut in a spaceship the sky appears black due to:

A
Absence of atmosphere in his neighbourhood

B
Light from the sky is absorbed by the medium surrounding him

C
The fact at the height, sky radiations are only in the infra-red and the ultraviolet region

D
None of these

Solution

To an astronaut it will appear as black.On earth we see the blue sky due to presence of atmosphere. Atmosphere refracts light ray coming from the sun and we see the colour of sky.In space, due to the absence of the atmosphere the light rays do not refract and reach the astronomer's eyes therefore it appears black.
Question 6
1 / -0

A small air bubble in a glass block when seen from above appears to be raised because of:

A
refraction of light

B
reflection of light

C
reflection and refraction of light

D
none of the above

Solution

A spherical air bubble in glass would actually act just like a diverging lens - that is, if we looked through the bubble the object would always be upright but would be smaller than the object really was. This is due to refraction of light.
Question 7
1 / -0

The instrument that is based on the principle that when an object is placed between first principal focus and the optic centre of convex lens, an upright, virtual and enlarged image on the same side of the object is formed, is

A
Telescope

B
Projector

C
Camera

D
Simple microscope

Solution

In astronomical telescope, convex lens called eyepiece, and objective lens are used and object is placed before eyepiece lens, such that final image inverted, a camera and eye also form inverted image on the screen. Whereas simple microscope gives an erect, virtual and enlarged image of the object placed between first principal focus and the optic nerve of the convex lens. In a projector, the image formed is real, inverted magnified on the other side of the lens. This inverted image is again inverted by the film.
Question 8
1 / -0

An object in a denser medium when viewed from a rarer medium appears to be raised. The shift is maximum for :

A
red light

B
violet light

C
yellow light

D
green light

Solution

An object in a denser medium when viewed from a rarer medium appears to be raised. This is due to refraction.
The dispersion of white light into a spectrum occurs because the different colors are refracted by different amounts by the water medium. Violet light is refracted most by the medium and red light is refracted least.
Below is the diagrammatic representation.
Question 9
1 / -0

A ray of light $$OP$$ passes through a right angled prism as shown in the adjacent diagram. State the angles of incidence at the faces $$AC$$ and $$BC$$. Given critical angle is $$42^o$$.

A
Angle of incidence at the face $$AC=45^o$$ and angle of incidence at the face $$BC=90^o$$

B
Angle of incidence at the face $$AC=90^o$$ and angle of incidence at the face $$BC=45^o$$

C
Angle of incidence at the face $$AC=45^o$$ and angle of incidence at the face $$BC=0^o$$

D
Angle of incidence at the face $$AC=0^o$$ and angle of incidence at the face $$BC=45^o$$

Solution

OP is incident normally on face AB and strikes AC undeviated. Since $$\angle{AQP}=45^o$$ (total internal angle of a triangle is $$180^o$$), the angle of incidence will be $$45^o$$. Since, critical angle for glass prism is $$42^o$$ the ray undergoes total internal reflection with an angle of reflection of $$45^o$$. It then strikes BC normally and hence angle of incidence at that face is $$0^o$$.
Question 10
1 / -0

A beam of light consisting of red, green and blue colours is incident on a right-angled prism as shown. The refractive index of the material of the prism for the above red, green and blue wavelengths are 1.39, 1.44 and 1.47 respectively. The prism will

A
seperate part of the red colour from the green and blue colours.

B
seperate part of the blue colour from the red and green colours.

C
seperate all the three colours from one another.

D
not seperate even partially any colour from the other two colours.

Solution

Difference in refractive indices of blue and green colour are less so they are seen together and red is seen separate because deviation depends on refractive index.