Double-slit interference
Let two coherent light waves meet and lay out bright and dark fringes on the screen.
A single beam of monochromatic light passing through two narrow slits produces two coherent sources. The path difference between the two beams decides how they superpose; the bright-fringe spacing is proportional to the wavelength and to the slit-to-screen distance, and inversely proportional to the slit separation.
Intensity vs. position on screen
The center is the zeroth-order bright fringe; the model does not include the single-slit diffraction envelope.
Think about it
Keeping the slit separation fixed, if the screen is moved to 2 times its original distance, how does the fringe spacing change?
The fringe spacing becomes 2 times its original value. From Δx = λL/d, the fringe spacing is proportional to the screen distance L.
Model assumptionsMonochromatic coherent light · Slit width neglected · Small-angle and far-field approximations · Equal intensity from both slits · Single-slit diffraction envelope ignored
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.