Refraction Of Light Through A Prism

Question 1

What is a prism?

Answer 1

A prism is a transparent medium bounded by five plane surfaces with a triangular cross section

Question 2

Which are the refracting surfaces of a prism?

Answer 2

The two rectangular polished surfaces inclined towards each other

Question 3

What is the condition of the base of a prism?

Answer 3

It is usually grounded or made rough

Question 4

What is the angle of prism?

Answer 4

The angle formed by the inclination of the two refracting surfaces of the prism on each other

Question 5

What represents the prism in ray diagrams?

Answer 5

Its principal section ABC

Question 6

What happens to the monochromatic ray in each refraction in a prism?

Answer 6

It bends towards the base of the prism

Question 7

What is the angle of deviation?

Answer 7

When a ray of light travels through a prism, it suffers refraction at two surfaces and deviates by an angle, which is formed between the incident ray (produced forward) and the emergent ray (produced backward)

Question 8

What is the angle of deviation denoted by?

Answer 8

The Greek alphabet δ (delta)

Question 9

Give the formula for the angle of deviation

Answer 9

δ = (i1 + i2) - (r1+r2)
Here, r2 - second angle of incidence
i2 - angle of emergence

Question 10

r1 + r2 = ?

Answer 10

A

Question 11

Give the formula to find angle of deviation from angle of prism

Answer 11

i1 + i2 = A + δ

Question 12

Why is the emergent ray not parallel to the incident ray in the prism?

Answer 12

In a prism, the refraction of light takes place at two inclined surfaces, so the emergent ray is not parallel, but deviated towards the base of the prism

Question 13

Name the factors affecting the angle of deviation

Answer 13

1. the angle of incidence
2. the material of prism ( on refractive index μ)
3. the angle of prism (A)
4. the color or wavelength (λ) of light used

Question 14

What happens to the angle of deviation on change in the angle of incidence?

Answer 14

As the angle of incidence increases, the angle of deviation first decreases, reaches to a minimum value for a certain angle of incidence and then on further increasing the angle of incidence, the angle of deviation begins to increase

Question 15

What is done to get the graph showing the variation of angle of deviation with the angle of incidence experimentally?

Answer 15

The direction of incident ray is kept unchanged and the prism is rotated. On rotation of the prism, the direction of normal at the face of the prism changes, so the angle of incidence changes

Question 16

When does the angle of deviation become minimum?

Answer 16

When the angle of incidence is equal to the angle of emergence, i.e., when i1 = i2 or r1 = r2

Question 17

What is the position of minimum deviation?

Answer 17

The position of a prism with respect to the incident ray at which the incident ray suffers minimum deviation

Question 18

What happens to the refracted ray in the position of minimum deviation?

Answer 18

The refracted ray inside the prism is parallel to its base

Question 19

What are the conditions required for the refracted ray to be parallel to the base of the prism?

Answer 19

1. The prism is equilateral
   OR
2. The principal section of the prism forms an isosceles triangle

Question 20

What is the formula for calculating the minimum deviation?

Answer 20

δmin = 2i - A

Question 21

Why is δmin unique for a given prism and a given color of light?

Answer 21

Only one horizontal line can be drawn parallel to the i-axis at the lowest point of i - δ curve, i.e., only for one value of angle of incidence i =, the refracted ray inside the prism is parallel to its base

Question 22

Give the steps for calculating r1, r2, i2, δ when refractive index and angle of incidence are given

Answer 22

1. For refraction at first face, μ = sin i/sin r - r1 obtained
2. r1 + r2 = A, so r2 is calculated
3. For ref. at 2nd face, 1/μ = sin r2/ sin i2 - i2 obtained
4. Thus, δ = (i1 + i2) - A

Question 23

How does minimum deviation depend on the material of prism?

Answer 23

For a given angle of incidence, a prism with a higher refractive index produces greater deviation than a prism with lower refractive index.

Question 24

Why does a flint glass prism produce greater deviation than a crown glass prism?

Answer 24

The refractive index of flint glass is higher than crown glass

Question 25

How does the angle of deviation depend on the angle of prism?

Answer 25

The angle of deviation increases with the increase in the angle of the prism (A)

Question 26

What is the angle of deviation for a small angle of prism?

Answer 26

δ = (μ-1)A

Question 27

How does the angle of deviation depend on the color or wavelength of light?

Answer 27

The refractive index of a given transparent medium decreases with the increase in wavelength of light. Thus, for visible light the refractive index of the material of a prism is maximum for violet color and minimum for red color. Consequently, a given prism deviates violet light the most and red light the least.

Question 28

For which lights is the RI highest and lowest? Why?

Answer 28

RI is highest for violet color as RI increases with decrease in wavelength of light and violet has slowest speed, and thus, lowest wavelength

RI is lowest for red color as it decreases with the increase in wavelength and speed