Optics
Single-slit diffraction
A single slit spreads light into a broad central maximum with dimmer side lobes; the first dark band is at a·sinθ = λ.
Single-slit diffraction — interactive Optics simulation. A single slit spreads light into a broad central maximum with dimmer side lobes; the first dark band is at a·sinθ = λ.
Single-slit diffraction
A single slit spreads light into a broad central maximum with dimmer side lobes; the first dark band is at a·sinθ = λ.
A single aperture diffracts light into a sinc-shaped pattern. The first dark fringe occurs when a sin θ = λ, setting the angular width of the central lobe. Narrower slits widen the pattern—limit to optical resolution and the basis of diffraction gratings.
- a sin θ = mλ
- Broad central max
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
Light passing through a SINGLE narrow slit also spreads into a pattern on a screen (diffraction), with a bright central band flanked by dimmer fringes. Does a wider slit spread this diffraction pattern more or less than a narrower slit?
Predictions to weigh
- Less — a wider slit produces a narrower, more tightly confined diffraction pattern.
- A wider slit spreads the pattern more.
- Slit width doesn't affect the diffraction pattern's spread.
Variable roles
What you set:
- Slit width a (µm)
What you measure:
- First minimum position y (mm)
How the investigation runs
- Open the single-slit preset and press Reset. Light wavelength is 550 nm; the screen sits 100 cm from the slit.
- Enable the first-minimum position readout.
- Set the slit width for each trial and record the position of the first dark fringe (minimum).
Governing equation
Single-Slit First Diffraction Minimum — a·sinθ = mλ
A single slit of width a produces its first dark fringe (minimum) at angle/position y = λL/a on a screen at distance L — the SAME formula shape as double-slit fringe spacing, but governed by the slit's own width rather than a separation between two slits.
What the printable worksheet asks students to work out
- For one trial, compute y = λL/a using λ = 550 nm, L = 100 cm (converting units to get y in mm — this is the position of the FIRST dark fringe, m = 1). Compare to the table.
- Compare this formula's shape to the double-slit fringe formula, but notice it uses the single slit's WIDTH a rather than a separation between two slits. Explain why a narrower single slit produces a WIDER central diffraction pattern — counter to intuition, but consistent with the same 1/width scaling.
Where this shows up beyond the lab
- This same physics (narrower apertures diffract light more) sets a fundamental limit on how sharply any lens or telescope can focus or resolve fine detail — the diffraction limit. Explain why a bigger telescope aperture (like the double-slit's wider spacing) gives sharper resolving power, not blurrier.
- A single slit's diffraction pattern has one central bright band with progressively dimmer side bands; a double slit's interference pattern has many closely-spaced bright fringes of similar brightness, all riding within a broader single-slit diffraction envelope. Explain why a real double-slit experiment (with slits of nonzero width) actually shows BOTH effects combined.
- AP Physics 2 — Unit 14: Waves, Sound, and Physical Optics
- IB Physics — C.3 Wave phenomena
- General High School Physics — Light & optics
- NGSS High School Physics — Wave properties
- Welcome to Single Slit
- Select the slit
- Press Play
- Broad central maximum
- Open the Properties panel
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.