Prism Colour Deviation
Under exam pressure learners get confused as to which one bends the most or least and make mistakes. Especially in assertion questions where they have to identify whether given statements are true and whether one supports or provides eviidence for the other, this confusion increases. It will be better if they visualize images related to this bit of information. Such images stay in the memory for a longer time and are unlikely to be forgotten even under pressure.
Assertion Question:
Assertion (A): The light of violet colour deviates the most and the light of red colour the least, while passing through a prim.
Reason (R):The refractive index in highest for red light and lowest for the violet light.
Prism Colour Deviation - NCERT Class X
"You have seen that white light is dispersed into its seven-colour components by a prism. Why do we get these colours? Different colours of light bend through different angles with respect to the incident ray, as they pass through a prism. The red light bends the least while the violet the most. Thus the rays of each colour emerge along different paths and thus become distinct. It is the band of distinct colours that we see in a spectrum." (NCERT Class X Physics)
Under exam pressure learners get confused as to which one bends the most or least and make mistakes. Especially in assertion questions where they have to identify whether given statements are true and whether one supports or provides eviidence for the other, this confusion increases. It will be better if they visualize images related to this bit of information. Such images stay in the memory for a longer time and are unlikely to be forgotten even under pressure.
For example, to remember
violet light suffers maximum (maxi dress) deviation and
red light suffers minimum (mini dress) deviation,
they can imagine a person with a full length, violet maxi dress and another in a short, red mini dress.
Violet most deviated colour.
Violet light suffers maximum deviation.
Red least deviated colour.
Red light suffers minimum deviation.
Red light bends the least.
Violet light bends the most.
Wave length is inversely proportionate to deviation.
More deviation - Less Wavelength
Less deviation - More Wavelength
Red - Least Deviation - Highest Wavelength
Violet - Most Deviation - Least Wavelength
Sample Assertion Question
Assertion (A): The light of violet colour deviates the most and the light of red colour the least, while passing through a prim.
Reason (R):The refractive index is the highest for red light and the lowest for the violet light.
Answer:
Assertion (A) is correct.
Reason (R) is incorrect.
Explanation:
Assertion (A): When white light passes through a prism, it gets dispersed into its constituent colors (violet, indigo, blue, green, yellow, orange, red). This phenomenon is called dispersion. The amount of deviation (bending) experienced by each color depends on its wavelength. Violet light, having the shortest wavelength, bends the most, while red light, with the longest wavelength, bends 1 the least.
Reason (R): The refractive index of a medium for a particular color of light is inversely proportional to the wavelength of that light. This means that a higher refractive index corresponds to a shorter wavelength. Therefore, violet light, with the shortest wavelength, should have the highest refractive index, and red light, with the longest wavelength, should have the lowest refractive index.
Conclusion:
The Assertion is correct, but the Reason is incorrect. The correct reason would be that the refractive index of a medium is higher for violet light and lower for red light.
More Resources for Assertion Reason Questions
https://www.teachoo.com/15646/3631/Question-5/category/Assertion-Reasoning-Questions-MCQ/
https://brainly.in/question/27858486
https://www.toppr.com/ask/question/in-the-dispersion-of-white-light-from-a-prism-the/