Science calculator
Double-slit interference.
Find an interference maximum angle or the spacing of neighbouring fringes on a distant screen. Enter all but one value.
Maximum angle θSolved
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bright-fringe geometry
- Path difference d sin θ
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- n integer maximum order · λ wavelength · d centre-to-centre slit separation · θ angle from the central axis · Δy fringe spacing · L screen distance
Assumptions
- Two coherent sources with the same wavelength and a stable phase relationship.
- Slit separation d is centre to centre; slit width is small enough that its diffraction envelope does not remove the fringe of interest.
- The exact maximum condition uses integer order n and angle measured from the central axis.
- The screen-spacing equation additionally uses the small-angle, distant-screen approximation: d and |y| are small compared with L.
How it works
A bright fringe occurs when the path difference from the two slits is a whole number of wavelengths. The central maximum is order zero.
On a distant screen at small angles, sin θ and tan θ are both approximately θ. This turns the exact angular condition into an almost uniform linear fringe spacing.
Choose the exact angle or approximate screen relationship and leave one field blank. A solved non-integer order does not correspond to a bright maximum.
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