Refraction Through Prism MCQs Quiz | Class 10
This quiz is designed for Class X Science (Code 086) students, covering Unit III: Natural Phenomena. Focus areas include Ray bending, deviation, and basic concepts of refraction through a prism. Test your understanding with 10 multiple-choice questions. Submit your answers and download a detailed PDF of your results with correct explanations.
Understanding Refraction Through a Prism
A prism is a transparent optical element with flat, polished surfaces that refract light. The most common type is a triangular prism, which has a triangular base and rectangular sides. When light passes through a prism, it undergoes refraction, causing it to bend and, for white light, to split into its constituent colors.
Ray Bending
When a ray of light enters a prism, it travels from a rarer medium (air) to a denser medium (glass). According to Snell’s Law, the light ray bends towards the normal at the first refracting surface. Upon exiting the prism, it travels from a denser medium (glass) to a rarer medium (air), bending away from the normal. Crucially, the overall effect is that the ray of light always bends towards the base of the prism.
Deviation of Light
Deviation is the change in the direction of the path of light as it passes through the prism. The angle of deviation (D) is the angle between the incident ray and the emergent ray. Several factors influence the angle of deviation:
- Angle of Incidence (i): The angle of deviation varies with the angle of incidence. There is a specific angle of incidence for which the angle of deviation is minimum (angle of minimum deviation, D_m).
- Angle of Prism (A): A larger angle of prism generally leads to a larger deviation.
- Refractive Index (n) of the material: Higher refractive index means more bending and thus greater deviation.
- Wavelength of Light: Different colors (wavelengths) of light travel at slightly different speeds in the prism material, leading to different refractive indices for each color. This causes different colors to deviate by different amounts, a phenomenon known as dispersion.
The relationship between the angle of incidence (i), angle of emergence (e), angle of prism (A), and angle of deviation (D) is given by the formula: i + e = A + D.
Basics of Prism Refraction and Dispersion
A prism has two refracting surfaces and a base. The angle between the two refracting surfaces is called the angle of the prism or refracting angle (A).
Dispersion of White Light:
White light is composed of seven constituent colors (VIBGYOR – Violet, Indigo, Blue, Green, Yellow, Orange, Red). When white light enters a prism, each color of light refracts at a slightly different angle due to their different wavelengths and, consequently, different refractive indices in the prism material. Violet light has the shortest wavelength and deviates the most, while red light has the longest wavelength and deviates the least.
This separation of white light into its spectrum of colors is called dispersion. It’s important to note that if monochromatic (single-colored) light is passed through a prism, it will only deviate but not disperse.
Deviation by Color:
| Color | Wavelength | Deviation |
|---|---|---|
| Violet | Shortest | Most |
| Red | Longest | Least |
Quick Revision
- Light bends towards the base of the prism.
- Angle of deviation is between the incident and emergent rays.
- Dispersion is the splitting of white light into its constituent colors.
- Violet light deviates the most, Red light deviates the least.
- Formula: i + e = A + D.
Extra Practice Questions
- Explain why a prism causes dispersion while a rectangular glass slab does not.
- What happens to the angle of deviation if the angle of incidence is increased from a very small value? (Consider the graph of deviation vs. incidence angle)
- Define the angle of minimum deviation for a prism and state the condition under which it occurs.
- List the factors that influence the angle of deviation produced by a prism.
- Draw a ray diagram showing the path of a monochromatic light ray through an equilateral prism, clearly marking the angle of incidence, refraction, and emergence.
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