Question

When white light is incident on a glass prism, the least deviated colour is \dots

• A. Red
• B. Violet
• C. Blue
• D. Green

Hint:

Remember the order VIBGYOR: \[ \text{Violet deviates most, Red deviates least} \] Longer wavelength means smaller deviation.

Answer 1

The Correct Option is A

Concept: When white light passes through a glass prism, it splits into different colours. This phenomenon is called dispersion of light. Different colours bend by different amounts because different colours have different wavelengths.

Step 1: Understand deviation in a prism. The amount of bending depends on the refractive index of glass for different colours.
• Smaller wavelength $\rightarrow$ greater deviation
• Larger wavelength $\rightarrow$ smaller deviation

Step 2: Compare red and violet light.
• Violet light has the shortest wavelength, so it bends the most.
• Red light has the longest wavelength, so it bends the least.

Step 3: Identify the least deviated colour. Therefore, the least deviated colour is: \[ \boxed{\text{Red}} \] Hence, the correct option is (1).