UPSC Prelims PYQ 2008: Assertion–Reason on red vs green light energy

Consider the following Assertion and Reason:

1. Assertion (A): In the visible spectrum of light, red light is more energetic than green light.
2. Reason (R): The wavelength of red light is more than that of green light.

Select the correct answer using the code given below:

1. Both A and R are individually true and R is the correct explanation of A
2. Both A and R are individually true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true

Explanation

Assertion (A) is false

• In the visible spectrum, red light is less energetic than green light. Energy is inversely proportional to wavelength (E=hc/lambda). Since red light has a longer wavelength, it possesses lower energy per photon. 

Reason (R) is true

• The wavelength of red light (approximately 620–750 nm) is indeed greater than that of green light (approximately 495–570 nm).

Answer: (d) A is false, but R is true