Single-slit and grating diffraction
The narrower the slit, the more light "bends" around it; the more slits, the sharper the bright fringes.
Light diffracts when it passes through a single slit. The central bright fringe on the screen is the widest and brightest, about 2λL/a wide: the narrower the slit and the longer the wavelength, the more pronounced the diffraction. N equally spaced slits form a grating; multi-slit interference places the principal maxima where d·sinθ = kλ. The more slits, the narrower and brighter the principal maxima, while the overall envelope is still set by single-slit diffraction.
This is a static model: forces and the graph update as soon as you change a parameter.
Relative intensity on the screen
The envelope comes from single-slit diffraction; the fine bright fringes inside it come from multi-slit interference.
Think about it
If the number of slits goes from 1 to 8, do the principal maxima move?
No. The positions of the principal maxima are set by the slit spacing d through d·sinθ = kλ; adding slits only makes the principal maxima narrower and brighter and the secondary maxima weaker.
Model assumptionsFraunhofer diffraction · screen distance 1 m · grating spacing 20 μm · intensity normalized
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.