Michelson's Interferometer

In the figure, two isotropic point sources $S_1$ and $S_2$ emit identical light waves in phase at wavelength $\mathrm{\lambda }$. The sources lie at separation $d$ on the $x$-axis and a light detector is moved in a circle of large radius around the midpoint between them. It detects $26$ points of zero intensity including two on the $x$-axis, one of them to the left of the sources and the other to the right of the sources. What is the value of $\frac{\mathrm{d}}{\mathrm{\lambda }}$?

In the figure, two radio-frequency point sources $S_1$ and $S_2$, separated by distance, $d=1.8 \mathrm{m}$, are radiating in phase with $\mathrm{\lambda }=0.50 \mathrm{m}$. A detector moves in a large circular path around the two sources in a plane containing them. How many (a) maxima and (b) minima does it detect?

The figure shows two isotropic point sources of light $(S_1$ and $S_2)$ that emit in phase at wavelength $500 \mathrm{nm}$ and at the same amplitude. A detection point $P$ is shown on the $x$-axis that extends through source $S_1$. The phase difference $\mathrm{\varphi }$ between the light arriving at point $P$ from the two sources to be measured as $P$ is moved along the $x$-axis from $x=0$ to $x=+\infty$. The results out to $x_{\mathrm{s}}=10\times {10}^{-7} \mathrm{m}$ are given in figure on the way out to $+\infty$. What is the greatest value of $x$ at which the light arriving at $P$ from $S_1$ is exactly out of phase with the light arriving at $P$ from $S_2$?

In the figure, two isotropic point sources of light $\left(S_1\right.$and$\left.S_2\right)$ are separated by distance $2.70 \mathrm{\mu m}$ along the $y$-axis and emit in phase at wavelength $900 \mathrm{nm}$ and at the same amplitude. A light detector is located at point $P$ at coordinate $x_{\mathrm{P}}$ on the $x$-axis. What is (a) the greatest value of $x_{\mathrm{P}}$ and (b) the second greatest value at which the detected light is minimum due to destructive interference?