Final answer:
The correct answer is (a) ½λ, as destructive interference occurs when the path difference between two coherent light sources is an odd multiple of ½λ.
Step-by-step explanation:
The question relates to the concept of destructive interference in the context of light waves and specifically with reference to double slit experiments. Destructive interference occurs when the path length difference between two waves is such that they cancel each other out. For a double slit setup, this path length difference must be a half-integral multiple of the wavelength (e.g., ½λ, ¾λ, ¹⁴λ).
Given the options provided for path differences, the correct answer for when destructive interference occurs is when the path difference is an odd multiple of ½λ (lambda over 2), such as ½λ, ¾λ, ½λ, and so on. The correct answer to this question is option (a) ½λ.