Test: Dispersion of Light - UPSC MCQ

When white light falls on a glass prism, each colour in it is refracted by a different angle, from which red colour is least deviated and violet most.

The differences in speed that each spectrum of light has as it passes through the medium causes different angles of refraction, which in turn causes dispersion. As the light leaves the prism it disperses even more due to the light speeding up again. Because each spectrum travels at different speeds while in the glass they don't reach the other side at the same time. So, the red spectrum exits first and speeds up first while the blue or violet spectrum exits last and speeds up last.

Angle of deviation is the deviation of moving objects which can be ray of light or solid object from its path after refraction or reflection. It measures how much something deviate from its path after it meets obstacles in its path.

The phenomena due to which white light splits Into seven colours on passing through a prism is called dispersion. Upon passing through a medium, each of the colors travels at different speeds and hence has different angles of refraction leading to the splitting of the light. 

When white light passes through a glass prism, it undergoes dispersion, which is the splitting of light into its component colors. This phenomenon is due to the different wavelengths of light being refracted by different amounts, resulting in the formation of a spectrum of colors.

• Option A: (a) Violet - First colour in VIBGYOR: This is the correct pair. Violet is the first colour in the VIBGYOR sequence.
• Option B: (b) Red - First colour in VIBGYOR: This is incorrect. Red is the last colour in the VIBGYOR sequence, not the first.
• Option C: (c) Green - Second colour in VIBGYOR: This is incorrect. Green is the fourth colour in the VIBGYOR sequence, not the second.
• Option D: (d) Yellow - Last colour in VIBGYOR: This is incorrect. Yellow is the fifth colour in the VIBGYOR sequence, not the last.

Therefore, the correctly matched pair is Option A: (a) Violet - First colour in VIBGYOR.

• Statement (i) is correct as the incident ray is indeed the ray of light that enters the prism.
• Statement (ii) is also correct because the refracted ray is the ray of light that bends as it passes through the prism material.
• Statement (iii) is accurate as the emergent ray is the ray of light that exits the prism after refraction.
• However, statement (iv) is incorrect because the splitting of white light into its component colors is known as dispersion, not refraction. Therefore, the correct statements are (i), (ii), and (iii).

Isaac Newton used a glass prism to obtain the spectrum of sunlight. He observed that when sunlight passes through a prism, it splits into its constituent colors, revealing the rainbow of colors that make up white light.

Isaac Newton was the first to use a glass prism to obtain the spectrum of sunlight. This observation led Newton to the idea that sunlight is made up of seven colors.

• Option A: Newton - Discovered that sunlight is composed of seven colors. This option is incorrectly matched. Isaac Newton indeed discovered that sunlight is composed of seven colors by using a glass prism.
• Option B: Red light - Bends the most through a prism. This option is incorrect. Red light bends the least through a prism, while violet light bends the most.
• Option C: Water droplets - Cause a rainbow by refracting and reflecting sunlight. This option is correctly matched. Water droplets in the atmosphere act like small prisms. They refract and disperse the incident sunlight, reflect it internally, and then refract it again, leading to the formation of a rainbow.
• Option D: Rainbow - Formed in the same direction as the Sun. This option is incorrect. A rainbow is formed in a direction opposite to that of the Sun. Thus, the correctly matched pair is Option C.