Prism and Dispersion

topicmedium9 MCQ

Deviation, angle of minimum deviation and dispersion of white light; scattering. (Physics › Ray Optics and Optical Instruments, NEET UG syllabus.)

What is Prism and Dispersion?

A transparent optical element with flat, polished surfaces that refract light.

Key formula / rule: Angle of Deviation (general)

Define a prism and explain its action on light.
Derive and apply the formula for the angle of deviation.
Explain the concept of minimum deviation and its conditions.
Derive and apply the formula for refractive index in terms of prism angle and minimum deviation.

Confusing deviation with dispersion; deviation is change in path, dispersion is splitting of colors.

Term: Prism
Meaning: A transparent optical element with flat, polished surfaces that refract light.

Term: Angle of Deviation (δ)
Meaning: The angle between the incident ray and the emergent ray from a prism.

Term: Angle of Minimum Deviation (δ_m)
Meaning: The smallest possible angle of deviation for a given prism and wavelength, occurring when the ray passes symmetrically through the prism.

Term: Dispersion
Meaning: The phenomenon of splitting white light into its constituent colors when it passes through a prism, due to the refractive index's dependence on wavelength.

Term: Angular Dispersion (θ)
Meaning: The difference in the angles of deviation for two extreme colors (e.g., violet and red) produced by a prism.

Term: Dispersive Power (ω)
Meaning: A measure of a material's ability to disperse light, defined as the ratio of angular dispersion to the mean deviation (usually for yellow light).

Term: Scattering of Light
Meaning: The phenomenon in which light rays are redirected in various directions when they strike particles of matter.

Define a prism and explain its action on light.
Derive and apply the formula for the angle of deviation.
Explain the concept of minimum deviation and its conditions.
Derive and apply the formula for refractive index in terms of prism angle and minimum deviation.
Explain the phenomenon of dispersion of light through a prism.
Relate dispersion to the wavelength dependence of refractive index.
Define and calculate angular dispersion and dispersive power.
Differentiate between deviation, dispersion, and scattering.
Solve numerical problems involving prisms, deviation, and dispersion.

Name: Angle of Deviation (general)
Note: Where i is angle of incidence, e is angle of emergence, A is prism angle.
Expression: δ = i + e - A

Name: Angular Dispersion
Note: Difference in deviation for violet and red light, for a thin prism. n_v and n_r are refractive indices for violet and red light.
Expression: θ = δ_v - δ_r = (n_v - n_r)A

Name: Dispersive Power
Note: Ratio of angular dispersion to mean deviation. n_y is refractive index for yellow (mean) light.
Expression: ω = (n_v - n_r) / (n_y - 1)

Confusing deviation with dispersion; deviation is change in path, dispersion is splitting of colors.
Incorrectly applying the condition for minimum deviation (i=e, r1=r2).
Mixing up the order of colors in the spectrum or their relative deviations.
Not understanding that dispersion is due to the wavelength dependence of the refractive index.
Using the small angle prism formula for large prism angles.
Forgetting the relationship between prism angle, angle of incidence, and angle of deviation.

What is the phenomenon called when white light splits into its constituent colours upon passing through a prism?…
easy
When white light passes through a prism, which colour deviates the most?…
easy
For a prism, the angle of minimum deviation occurs when:…
easy