Refraction of light through a glass prism

Question 1

describe the shape of triangular prism

Answer 1

it is a transparent object. It has 2 triangular bases and 3 rectangular lateral surfaces. these lateral faces are inclined to each other. the angle between two lateral faces is called the angle of prism.

Question 2

what are the results of the refraction of light through glass prism

Answer 2

i) the light ray undergoes 2 times refraction: the first time is from air to glass and second time is from glass to air.
ii) since the prism has 2 traingular bases and 3 lateral rectangular surfaces which are inclined to each other, the refraction of light is done by non-parallel sided.
iii) the angle between the two lateral sides is caled the angle of the prism. The light ray after refraction is parallel to the base but the light emerging out bends towards the base.
iv) due to the peculiar shape of the prism, the emergent ray of light bends at an angle in the direction of the incident ray.this angle is called the angle of the deviation.
v) the angle between the path of the incident ray and the emergent ray is called the angle of deviation. it depends on
a) angle of prism
b) angle of incidence
c) colour/wavelength of light
d) optical density of the material of the prism

vi) in a prism
∠i +∠e=∠a+∠d
vii) angle of deviation of red light is minimum and that of violet light is maximum

Question 3

why is the emergent ray bending towards the base

Answer 3

since the second time refraction was from glass to air, the light ray bends away from the normal that is also towards the base of the prism

Question 4

why is the emergent ray and incident ray not parallel in the case of refraction of light by a triangular prism

Answer 4

The emergent ray of light in a prism is not parallel to the incident ray of light because the opposite faces of the glass prism are not parallel to one another.

Question 5

define spectrum

Answer 5

The band of seven colours formed on white screen, when a beam of white light is passed through a glass prism is called , is called spectrum of white light. The seven colours of spectrum are :Red, Orange, Yellow, Green, Blue, Indigo and Violet.The seven colours of spectrum can be denoted by the word VIBGYOR.

Question 6

define dispersion

Answer 6

The splitting up of white light into its component(seven) colours on passing through a transparent medium like a glass prism is called dispersion of light.

Question 7

a prism causes dispersion while a rectangular glass slab doesnt. why is it so?

Answer 7

i) in a prism, the refraction of white light takes place at the slant or non-parallel surfaces. The dispersion of white light takes place at the first surface which causes its seven constituent colours to deviate through a different angle. At the second surface these split colours suffer through normal refraction and get seperated.
ii) where as in a glass slab, the refraction of light takes place at the opposite parallel sides. At the first surface the white light is seperated into its seven constituent colours which undergoes an equal and opposite refraction at the second parallel surface, and emerges out as white colours.
iii) the rectangular glass slab is a combination of two glass prisms kept in contact with their refractive angles in opposite direction. Dispersion done by one glass prism is cancelled by the other. therefore dispersion does nto take place in a rectangular slab.

Question 8

what causes of dispersion of light

Answer 8

White light consist of seven colours (VIBGYOR). The wavelength of red colour is longest and the wavelength of violet the shortest. The speed of light depends upon wavelength or colour. If wavelength of a colour is large the speed of colour is also large. Therefore the speed of red colour in a medium is highest and the speed of violet colour is the least. Hence all colours of white light are refracted by different amounts while passing through prism. Therefore, when white light passes through a glass prism, different constituent colours come out at different angles. This gives rise to dispersion of light.

Question 9

what causes dispersion of light tb

Answer 9

different colours of white light bend through different angles with respect to the incident ray as they pass through a glass prism. the red colout bends the least while violet bends the most. theyrays of each colour emerge along different paths and thus become distinct.

Question 10

explain isaac newton;s experiemtn

Answer 10

isaac newton was the first to use a glass prism to obtain the spectrum of sunlight. he tried to further split the colours of the spectrum by using another glass prism. But he couldn’t obtain any more colours. So he placed the second identical prism in an inverted position with respect to the first prism. this allowed the light from the spectrum to pass through the second prism. he then observed a beam of white light emerged from the other side of the second prism. this observation made him conclude that sunlight consists of 7 colours.

Question 11

define whitelight

Answer 11

any light that gives a spectrum similar to the one by sunlight is called white light

Question 12

what is recombination of light

Answer 12

when a second identical glass prism is placed in an inverted position with respect to the first prism, the set up will be like a rectangular glass slab there the emergent light will be white light.

Question 13

what is the significance of newton;s experiment

Answer 13

the significance of his experiemnt is that the sunlight consists of 7 constituent colous that ger recombined when passing through a second prism.

Question 14

different colours of whitelight have a different angle of deviation. why

Answer 14

i) all the colours of white light (vibgyor) have different wavelengths varying from 400-700nm. Since speed of light is directly proportional to its wavelength, the speed of different colours vary when the enter the glass prism, because glass prism has varying optical density.
ii) the 7 colours in white light have the same speed when they are in air. When the enter the glass prism, the red light has longest wavelength, therefore highest speed and gets minimum angle of deviation while violet has shortest wavelength, slower speed and maximum angle of deviation

Question 15

describe about the natural spectrum

Answer 15

A rainbow is a natural spectrum appearing in the sky after a
rain shower (Fig. 11.7). It is caused by dispersion of sunlight by
tiny water droplets, present in the atmosphere. A rainbow is
always formed in a direction opposite to that of the Sun. The
water droplets act like small prisms. They refract and disperse
the incident sunlight, then reflect it internally, and finally refract
it again when it comes out of the raindrop (Fig. 11.8). Due to the
dispersion of light and internal reflection, different colours reach
the observer’s eye.

Question 16

what are the conditions need for formation fo rainbow

Answer 16

i) there should be sunlight after rainfall
ii) the rainbow should form on the side opposite to tht of the sun
iii) the observer should be in between the rain and sun

Question 17

what are the different phenomena involved in rainbow

Answer 17

i) 2 times refraction
air-water
water-air
ii) dispersion of light
iii)light is reflected internally.

Question 18

how else can a rainbow be formed

Answer 18

it can be formed by spray,fog,rain when sunlight fall on it

Question 19

why is the rainbow on the other side of the sun? why do we see it as a bow shape///
◉_◉

Answer 19

due to the internal reflection of light, we see a rainbow at the opposite side of the sun having red colour at the top and violet in the bottom.

the rinbow is actually circular in shap ebut since water reflects it by 180 degrees and refracts it by 42 degrees from our eye, we see the refracted/reflected light has a bow.

Question 20

what is a secondary rainbow

Answer 20

if sunlight is reflected 2 times in the water, drop a secondary rainbow is formed. It is more fainter and the order of colours is reversed.