Question

Two sources $S_1$ and $S_2$, emitting light of wavelength $600\text{nm}$, are placed a distance $1.0\times {10}^{-2}\text{cm}$ apart. A detector can be moved on the line $S_{1}P$, which is perpendicular to $S_1{S}_2$. What would be the minimum path difference (Approximately) at the detector, as it moves along the line $S_{1}P$?

• A. $\text{zero}$
• B. $d$
• C. $d/2$
• D. $\text{infinity}$

Answer 1

The correct option is A $\text{zero}$

Path difference at $P$ is given by :
$\Delta x=S_{2}P-S_{1}P$


Minimum path difference will occur when the detector will be at a large distance from both the sources. The path difference will be maximum $(\Delta x_{max}=d)$ when the detector is at the source $S_1$. As detector moves away from $S_1$ , towards $+x-$direction, the path difference goes on decreasing.
At infinite distance from $S_1$ (theoretically), the path difference will be approximately equal to zero.

Hence, option $\left(A\right)$ is the correct answer.