Ray Optics and Optical Test

Result

Ray Optics and Optical Test - 32

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Weekly Quiz Competition

Question 1
1 / -0

The radius of curvature of a plane mirror is:

A
zero

B
infinite

C
negative

D
finite

Solution

A plane mirror may be considered to be a part of an infinitely large spherical surface.
And, an infinitely large spherical surface will have infinite radius.
So, radius of curvature for a plane mirror will be infinite.
Question 2
1 / -0

The twinkling of stars is due to atmospheric

A
Refraction of light

B
Reflection of light

C
Scattering of light

D
Dispersion of light

Solution

Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the earth atmosphere.
Stars appear as tiny dots in the sky; as their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions (light is bent when it hits a change in density - like a pocket of cold air or hot air). This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling).
Option A is correct.
Question 3
1 / -0

A mirage occurs because

A
The refractive index of atmosphere increases with height

B
The refractive index of atmosphere decreases with height

C
The hot ground acts like a mirror

D
Refractive index remains constant with height

Solution

$$Answer:-$$ A
As hot air rises above cold air descends so as we move upward refractive index also decreases .
For exhausted travelers in the desert, an inferior mirage may appear to be a lake of water in the distance. An inferior mirage is called "inferior" because the mirage is located under the real object. The real object in an inferior mirage is the (blue) sky or any distant (therefore bluish) object in that same direction. The mirage causes the observer to see a bright and bluish patch on the ground in the distance.
Light rays coming from a particular distant object all travel through nearly the same air layers and all are bent over about the same amount. Therefore, rays coming from the top of the object will arrive lower than those from the bottom. The image usually is upside down, enhancing the illusion that the sky image seen in the distance is really a water or oil puddle acting as a mirror.
Question 4
1 / -0

A ray of light is incident on a hollow glass prism as shown. Then the ray will undergo :

A
deviation and dispersion both

B
deviation but not dispersion

C
dispersion but no deviation

D
neither deviation nor dispersion

Solution

Answer is D
Surfaces of the hollow prism behaves like glass slabs thus there is no dispersion. The incident light is refracted through the glass slab.
Hence, when a ray of light is incident on a hollow glass prism, there will be neither dispersion nor deviation.
Question 5
1 / -0

An under-water swimmer cannot see very clearly even in absolutely clear water because of:

A
Absorption of light in water

B
Scattering of light in water

C
Reduction of speed of light in water

D
Change in the focal length of eye lens.
Question 6
1 / -0

Which one of the following statements is correct?

A
The planets twinkle at night due to atmospheric refraction of light

B
The stars appear higher in the sky than they actually are, due to scattering of light

C
The blue colour of sky is due to scattering of light

D
The rainbow is produced by the reflection of white sunlight by water drops in the atmosphere.

Solution

The blue colour of the sky is due to the scattering of light by small particles of the atmosphere (air molecules). When white light (from the sun) enters the earth's atmosphere, it gets scattered away due to the atmospheric particles. Since blue colour has the minimum wavelength, so blue colour scatters the most and thus the sky appears blue.
Question 7
1 / -0

Light enters an isosceles right triangular prism at normal incidence through face AB and undergoes total internal reflection at face BC as shown below :
The minimum value of the refractive index of the prifsm is close to:

A
$$1.10$$

B
$$1.55$$

C
$$1.42$$

D
$$1.72$$

Solution

$$n_1=1 ; n_2=? ; \theta_1=90^0 ; \theta_2=45^0$$
using snell's law
$$n_1sin\theta_1=n_2sin\theta_2$$
$$n_2=\frac{sin90^0}{sin45^0}$$
$$n_2=1.414$$
hence,The minimum value of the refractive index of the prism is close to 1.42.
Question 8
1 / -0

The term refraction of light is best described by:

A
The bending of light rays when they enter from one medium to another medium

B
Splitting of white light into seven colours when it passes through the prism

C
Bending of light round corners of obstacles and apertures

D
Coming back of light from a bright smooth surface

Solution

When light enters from one medium to another, its speed and direction changes. This phenomenon of bending of light rays while going from one medium to another is called refraction.
Question 9
1 / -0

The distance between the extreme points on the periphery of the mirror is called :

A
focal length

B
radius of curvature

C
aperture

D
pole

Solution

The reflecting surface of a spherical mirror has a circular outline. The diameter of the reflecting surface of spherical mirror is called its aperture. It is also the distance between extreme points on the periphery of the mirror.

So option (C) is correct.
Question 10
1 / -0

A coin is placed at the bottom of a glass tumbler and then water is added. It appeared that the depth of the coin has been reduced because

A
The water has made the coin lighter

B
The water is a different medium and has affected the path of light due to refraction

C
The water has affected the phenomenon of reflection of light

D
The water has affected the phenomenon of scattering of light

Solution