Labs / Physics
Two-Source Interference
Two sources ripple in step, and where their crests meet you get bright constructive lines; where a crest meets a trough the water goes still. Drag the probe through the field to read the path difference, and watch the fringes on the screen slide as you change the spacing, wavelength, or phase.
Δr 0.0 cmat probe —fringe 0.0 cm
What to try
- Move the sources closer together. Do the bright fringes on the screen spread apart or crowd together — and can you predict which before you drag?
- What happens to the whole pattern when you push the phase to 180°? Where does the center of the screen go from bright to dark?
- Park the probe on a bright antinodal line. What is its path difference in wavelengths, and is that number always a whole number?
- Stretch the wavelength longer. Why do fewer, wider fringes appear even though the sources never moved?
- Can you find a setting where the very middle of the screen is dark? What does that tell you about the two waves arriving there?