Double-Slit Interference

d\sin\theta = m\lambda

Condition for constructive interference (bright fringes) in Young's double-slit experiment.

Variables

Slit separation

Allowed values: greater than 0

Angle to maximum

Order number

Allowed values: 0 or more, whole number

unitless

Wavelength

Allowed values: greater than 0

Derivation

Derived from path difference between light from two slits being an integer multiple of wavelength.

Your notes

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Other optics formulas with the same quantities

Diffraction Grating (Wave Optics) shares Angle to maximum, Order number, Wavelength
Resolving Power of Grating (Wave Optics) shares Wavelength, Order number
Thin Film Interference (Wave Optics) shares Order number
Constructive Interference Condition (Wave Optics) shares Wavelength
Rayleigh Criterion (Resolution) shares Wavelength

Where this formula is listed

Optics formulas, under Wave Optics, alongside Optical Path Length.
In the optics list it comes after Combined Lens Power and before Fringe Spacing.
Optics formula sheet, one of 34 formulas printed with symbol keys and SI units.
The full formula index, grouped by category and topic.

Common questions

What is the Double-Slit Interference formula?

Double-Slit Interference is written d sin θ = mλ. Condition for constructive interference (bright fringes) in Young's double-slit experiment. It belongs to Optics, under Wave Optics.

What are the units in d sin θ = mλ?

In SI units, d is slit separation, measured in m; θ is angle to maximum, measured in °; m is order number (dimensionless); λ is wavelength, measured in m.

How is the Double-Slit Interference formula derived?

Derived from path difference between light from two slits being an integer multiple of wavelength. The result is d sin θ = mλ.