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The angle of deviation depends on the angle of incidence. If there is an increase in the angle of incidence, the angle of deviation decreases and at a particular angle of incidence, it becomes minimum.
- The minimum value of the angle of deviation is called “the angle of minimum deviation of the prism”.
- The position of the prism at a minimum angle of deviation is known as the “minimum deviation position”.
- There is one and only one angle of incidence for which the deviation produced by the prism is minimum.
- In the position of minimum deviation, the prism lies symmetrically with respect to the incident ray of light.
- When the prism is in the minimum deviation position, the refracted ray inside the prism is parallel to the prism’s base and the angle of incidence is equal to the angle of emergent.
Ques. What is a prism?
Ans. A prism is a homogeneous transparent refracting medium bounded by at least two nonparallel plane surfaces inclined at some angle.
Ques. What is meant by the angle of deviation?
Ans. The angle of deviation is the angle through which the incident ray is turned while passing through the prism.
Ques. What are the different factors on which the angle of deviation depends?
Ans. The following are the factors on which the angle of deviation depends are
- Refractive index (µ)
- The angle of incidence (i)
- The wavelength of light (λ)
- The angle of the prism (A)
Ques. What are the materials required for this experiment?
Ans. The materials required for this experiment are
- a drawing board
- drawing pins
- a white sheet of paper
- a prism
- office pins
- a pencil
- a half-meter scale
- graph paper.
- a protractor
Ques. Which colour deviates the most due to dispersion?
Ans. The colour that deviates the most due to dispersion is Violet.
Ques. What is dispersive power?
Ans. The dispersive power of a material is its ability to disperse the constituent's colours of incident light.
Ques. What is the formula of dispersive power?
Ans. The dispersive power is given by the ratio of the angular dispersion (θ) to the mean deviation (ẟ) produced by the prism.
Dispersive power, ω = θ/ẟ
Ques. What is meant by the dispersion of light?
Ans. The process of splitting white light into its constituent seven colours is known as the dispersion of light.
Ques. Which colour deviates the least due to dispersion?
Ans. The colour that deviates the most due to dispersion is red.
Ques. For which colour, the refractive index of glass is maximum?
Ans. The refractive index is inversely proportional to the wavelength of the light. The violet colour has the shortest wavelength. Therefore, its refractive index is maximum.
Ques. For which colour, the refractive index of glass is minimum?
Ans. The refractive index is inversely proportional to the wavelength of the light. The red colour has the longest wavelength. Therefore, its refractive index is minimum.
Ques. Define angular dispersion.
Ans. Angular dispersion is defined as the difference in the deviations suffered by the two extreme colours while passing through a prism.
Ques. On which factors does the dispersive power of a prism depend?
Ans. The dispersive power of a prism depends on the refractive index of the prism and it is independent of the shape and size of the prism.
Ques. Does a beam of white light give a spectrum on passing through a hollow prism?
Ans. A beam of white light does not show a spectrum while passing through a hollow prism because the dispersion of light cannot occur on passing through air contained in a hollow prism. Dispersion takes place because the refractive index of a medium for different colours is different.
Ques. What is the theory behind this experiment?
Ans. The theory behind this experiment is that when a ray of light moves through two adjacent mediums with different refractive indices or densities it undergoes refraction. This results in the deviation of the emergent light ray compared to the incident light ray.
Ques. How many edges are there in a prism?
Ans. In a triangular prism, there are 9 edges.
Ques. What is meant by the angle of minimum deviation?
Ans. As the angle of incidence increases, the angle of deviation decreases till it becomes minimum at a particular angle of incidence. The minimum value of the angle of deviation is called the angle of minimum deviation.
Ques. What is the condition of minimum deviation?
Ans. When the prism is in the minimum deviation position, the refracted ray inside the prism is parallel to the base of the prism and the angle of incidence is equal to the angle of emergent.
Ques. Does the colour of light influence the angle of minimum deviation?
Ans. Yes, the angle of minimum deviation is different for different colours or wavelengths of light.
Ques. What is the full form of VIBGYOR?
Ans. The full form of VIBGYOR is
- V: Violet
- I: Indigo
- B: Blue
- G: Green
- Y: Yellow
- O: Orange
- R: Red
Ques. Why are there dual values of incidence angle for one particular value of deviation angle?
Ans. In the case where an emergent light ray is reversed, then the angle i changes to e and the angle e changes to i. The reversed light ray will possess the exact deviation as before.
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