What quantity did you change?
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.
Labs / Physics / Two-Source Interference
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.
Why it matters
Why explore this?
Physics explains how changes in forces, energy, motion, and matter produce results we can measure. This model lets you test one part of that relationship at a time.
Explore
Try the model
Δr 0.0 cmat probe —fringe 0.0 cm
Investigate
Questions to test
Predict first, try it in the model, then use what you observe to answer.
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?
Explain
Make sense of what happened
Name the quantity you changed, the quantity that responded, and the physical rule connecting them. Use a readout or visible change as evidence.
Check
Before you leave
What measurable result changed?
Which physical idea connects them?
If you can answer all three using evidence from the model, you understand the main idea. If not, return to Explore and change one setting at a time.