# Class 12th Physics – 9 Ray Optics and Optical Instruments MCQs

#### A boy observing the image of a wall clock in a plane mirror reads the time as 2'o clock. The actual time shown by the clock is ____ 'o clock.

Correct! Wrong!

The image shown by plane mirror is virtual, erect and laterally inverted.
Hence, the correct reading of time = 12 - 2'o clock.
= 10'o clock.

#### A concave mirror has a focal length of 14 cm. When an object is placed in front of it, it produces a magnified image. The object distance ____.

Correct! Wrong!

A concave mirror produces a virtual image of an object when the object distance is either less than its focal length 'f' or between 'f' and '2f'. Hence (c) is the correct option.

#### When sunlight passes through atmosphere, light of ____ is scattered much more than light of ____.

Correct! Wrong!

When sunlight passes through atmospheric air, light of shorter wavelength is scattered much more than the light of longer wavelength.

#### The reflected light obeys ____ and the transmitted light obeys ___.

Correct! Wrong!

The reflected light obeys laws of reflection and the transmitted light obeys laws of refraction.

#### A person looking at a primary rainbow receives ____.

Correct! Wrong!

A person looking at a primary rainbow, receives different colours from different drops with red colour from the top drop and violet colour from the bottom drop.

#### Mirage formation on a hot sunny day is due to the fact that ______________.

Correct! Wrong!

On a hot sunny day, the layer of air closest to the earth is hottest. As we move up, we come across colder layers of air. The refractive index of colder layers of air is higher than that of the hotter layers of air. This can lead to formation of mirage.

#### If the incident ray and the reflected ray lie on xz-plane, the normal at the point of incidence lie in ____.

Correct! Wrong!

According to laws of reflection, incident ray, the normal and the reflected ray the entire lie in the same plane. Hence the normal also lies in xz-plane.

#### Human eye is sensitive to ____.

Correct! Wrong!

Human eye is not sensitive to any mechanical wave. It is sensitive to a range of electromagnetic waves known as "visible light".

#### The reflection of light that takes place on a smooth surface is known as ____ and that takes place on rough surface is known as ____

Correct! Wrong!

The reflection of light that takes place on a smooth surface is known as regular or specular reflection and that takes place on a rough surface is known as diffuse reflection.

#### ____ which of the following is not due to scattering of light?

Correct! Wrong!

Blue colour of the sky, white colour of clouds, reddish colour of the sun near the horizon is due to scattering of light. But brilliant colours of pearls are caused by diffraction of light.

#### The red and violet rays coming out of a raindrop after getting internally reflected twice makes ____ and ____ angles respectively with the incoming sunlight

Correct! Wrong!

The red and violet rays coming out of a raindrop after getting internally reflected twice, makes 50° and 53° respectively with the incoming sunlight.

#### From a side, a beam of laser light through atmospheric air is visible due to ____

Correct! Wrong!

From a side a beam of laser light through atmospheric air is visible due to scattering of light.

#### When a beam of light incident on an interface separating two transparent media, then ____.

Correct! Wrong!

When a beam of light is incident on an interface separating two transparent media, then a part of the light gets reflected and a part gets transmitted.

#### Due to atmospheric refraction, the sun is visible ____ seconds before the actual sun rays and ____ seconds after the actual sunset.

Correct! Wrong!

Due to atmospheric refraction, the sun is visible two minutes before the actual sunrise and two minutes after the actual sunset.

#### The phenomenon of ____ is not responsible for the formation of rainbow.

Correct! Wrong!

When sunlight enters the rain drop, it refracts and disperses into constituent colours. When incident on back surface of the rain drop it gets internally reflected. There is no role of scattering of light in the formation of rainbow.

#### For the primary rainbow ____ is at the outer edge and ____ is at the inner edge and for the secondary rainbow, ____ is at the outer edge and ____ is at the inner edge.

Correct! Wrong!

For the primary rainbow red colour is at the outer edge and violet is at the inner edge. Whereas, for the secondary rainbow, violet is at the outer edge and red is at the inner edge.

#### A mirror produces a virtual and erect image. Then its focal length is ____.

Correct! Wrong!

Plane mirror, concave mirror and convex mirror have the ability to produce virtual and erect images. A plane mirror has infinite focal length, concave mirror has positive focal length and convex mirror has negative focal length, according to the Cartesian sign convention.

#### Laws of reflection are obeyed by light in ____.

Correct! Wrong!

Laws of reflection are obeyed by light in either specular reflection or diffuse reflection.

#### A concave mirror has a focal length 12 cm. To obtain a real, inverted image which is the same size of that of object, the object distance should be ____cm.

Correct! Wrong!

A concave mirror produces a real, inverted image of same size as the object when the object is placed at distance of twice its focal length.
Therefore, object distance = 2f = 2 × 12 = 24 cm.

#### Converging beam of light forms a ____ and a diverging beam of light forms a ____

Correct! Wrong!

Conversing beam of light forms a real image where as a diverging beam of light forms a virtual image.

#### A small coin placed on a table is viewed through a microscope. When a glass slab is placed over the coin, the microscope is moved up through '4 cm' to focus the coin. Now, when the coin is removed from the bottom and placed on the top of the glass slab, the microscope is moved through a further distance of 8 cm in order to focus the coin the refractive index of the glass is ____.

Correct! Wrong!

Initially the microscope is focused on the coin
When glass slab is placed, the microscope is moved by 4 cm this is equal to the shift in the image. When the coin is placed at the top of the glass slab, the microscope is moved through 8 cm
then apparent depth = 8 cm
Real depth = apparent depth + shift
= 8 + 4 = 12 cm
Refractive index, μ = Real depth/apparent depth
=128
= 1.5

#### Which of the following is not due to refraction of sunlight through atmospheric air?

Correct! Wrong!

Red colour of the sun at horizon is due to scattering of light. Remaining all phenomena mentioned is due to refraction of light through atmosphere.

#### A concave mirror has a magnification ____

Correct! Wrong!

A concave mirror produces both magnified and diminished images depending on the object distance. Hence option 'C' is the right option.

#### A glass plate of 2 cm thickness is placed over a dot on a sheet of paper. When viewed normally from the top, the dot appeared 1.28 cm below the upper surface. The refractive index of glass is ____.

Correct! Wrong!

Refractive index = Real depth/apparent depth
=21.28
= 1.56

#### Lateral shift of a light ray refracted through a parallel sided glass slab depends on ____.

Correct! Wrong!

Lateral shift depends on angle of incidence, thickness of glass slab and also on the refractive index of glass. In fact it increases with increase in any of these parameters.

#### Statement A: Multiple total internal reflections cause diamond to shine. Statement B: Diamond has a very low critical angle of 24.4° approximately. State which of the statements are true.

Correct! Wrong!

The critical angle for diamond-air interface is 24.4°. Due to this low critical angle, when light enters a suitably cut diamond, multiple total internal reflectors occur, causing it to shine. Hence, both A and B are true.

#### Inside a raindrop, sunlight get internally reflected ____ in the formation of a primary rainbow and ____ in the formation of secondary rainbow.

Correct! Wrong!

Inside a raindrop, sunlight gets internally reflected once in the formation of a primary rainbow and twice in the formation of secondary rainbow.

#### In Rayleigh scattering, the amount of light scattered is ____.

Correct! Wrong!

According to Rayleigh scattering, the amount of light scattered α1/λ4 α1/λ4

#### Convex mirrors produce ____.

Correct! Wrong!

A convex mirror always produces virtual images irrespective of the object distance. The images are virtual, erect and diminished compared to the object.

#### In the formation of primary rainbow, the red and violet rays coming out of the water drop makes ____ and ____ angles with respect to the sunlight incident on the water drop.

Correct! Wrong!

In the formation of primary rainbow, the red and violet rays coming out of the water drop makes 42° and 40° angles with respect to the incoming sunlight.

Class 12th Physics - 9 Ray Optics and Optical Instruments MCQs
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Class 12th Physics - 9 Ray Optics and Optical Instruments MCQs