Refraction Of Light Through A Prism Flashcards
What is a prism?
A prism is a transparent medium bounded by five plane surfaces with a triangular cross section
Which are the refracting surfaces of a prism?
The two rectangular polished surfaces inclined towards each other
What is the condition of the base of a prism?
It is usually grounded or made rough
What is the angle of prism?
The angle formed by the inclination of the two refracting surfaces of the prism on each other
What represents the prism in ray diagrams?
Its principal section ABC
What happens to the monochromatic ray in each refraction in a prism?
It bends towards the base of the prism
What is the angle of deviation?
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)
What is the angle of deviation denoted by?
The Greek alphabet δ (delta)
Give the formula for the angle of deviation
δ = (i1 + i2) - (r1+r2)
Here, r2 - second angle of incidence
i2 - angle of emergence
r1 + r2 = ?
A
Give the formula to find angle of deviation from angle of prism
i1 + i2 = A + δ
Why is the emergent ray not parallel to the incident ray in the prism?
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
Name the factors affecting the angle of deviation
- the angle of incidence
- the material of prism ( on refractive index μ)
- the angle of prism (A)
- the color or wavelength (λ) of light used
What happens to the angle of deviation on change in the angle of incidence?
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
What is done to get the graph showing the variation of angle of deviation with the angle of incidence experimentally?
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
When does the angle of deviation become minimum?
When the angle of incidence is equal to the angle of emergence, i.e., when i1 = i2 or r1 = r2
What is the position of minimum deviation?
The position of a prism with respect to the incident ray at which the incident ray suffers minimum deviation
What happens to the refracted ray in the position of minimum deviation?
The refracted ray inside the prism is parallel to its base
What are the conditions required for the refracted ray to be parallel to the base of the prism?
- The prism is equilateral
OR - The principal section of the prism forms an isosceles triangle
What is the formula for calculating the minimum deviation?
δmin = 2i - A
Why is δmin unique for a given prism and a given color of light?
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
Give the steps for calculating r1, r2, i2, δ when refractive index and angle of incidence are given
- For refraction at first face, μ = sin i/sin r - r1 obtained
- r1 + r2 = A, so r2 is calculated
- For ref. at 2nd face, 1/μ = sin r2/ sin i2 - i2 obtained
- Thus, δ = (i1 + i2) - A
How does minimum deviation depend on the material of prism?
For a given angle of incidence, a prism with a higher refractive index produces greater deviation than a prism with lower refractive index.
Why does a flint glass prism produce greater deviation than a crown glass prism?
The refractive index of flint glass is higher than crown glass
How does the angle of deviation depend on the angle of prism?
The angle of deviation increases with the increase in the angle of the prism (A)
What is the angle of deviation for a small angle of prism?
δ = (μ-1)A
How does the angle of deviation depend on the color or wavelength of light?
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.
For which lights is the RI highest and lowest? Why?
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
