Question

For a wave train of wavelength \(\lambda\) having \(N\) number of wave oscillations, the coherence length is:

• A. \(\dfrac{\lambda}{N}\)
• B. \(N\lambda\)
• C. \(\lambda N^2\)
• D. \(\dfrac{N}{\lambda}\)

Hint:

If a wave train contains \(N\) waves of wavelength \(\lambda\), then its coherence length is \(N\lambda\).

Answer 1

The Correct Option is B

Concept:
Coherence length is the length over which a wave train maintains a definite phase relationship.

Step 1: Understand the wave train.
If one complete oscillation has wavelength: \[ \lambda \] and the wave train contains: \[ N \] complete oscillations, then total length of the wave train is obtained by multiplying the number of oscillations by wavelength.

Step 2: Apply the formula. \[ \text{Coherence length}=N\times \lambda \] \[ L_c=N\lambda \]

Step 3: Final answer. \[ \therefore \text{Correct Answer is (B)} \]