Young's Double Slit

600 nm

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You can adjust the spacing and position of the slits.

Young’s double slit experiment

Young’s interference experiment is as follows: The light diffracted from the small holes S₀ on-screen ‘A’ passes through the small holes S₁ and S₂.
Light passing through the two small holes overlaps between screens B and C, creating an interference fringe on screen C.

Constructive interference

When the waves arriving from the two slits are in the same phase, a bright pattern is formed.
To cause constructive interference, the path difference d·sin θ must be ‘0’ or an integer multiple of the wavelength.

Constructive interference

d \cdot s i n (θ) = n λ

$d\cdot sin(\theta )\,=\,n\lambda$ (n = 0, 1, 2…)
position

y_{n} = \frac{n λ D}{d}

${y }_{ n }\,=\,\frac {n\lambda D }{ d}$ (n = 0, 1, 2…)

d: Slit spacing (m)
θ: diffraction angle (rad)
λ: wavelength of light (m)
D: Distance from slit to screen (m)

When ‘n = 0’, the diffraction angle of the central axis ‘θ = 0’.

Destructive interference

When the waves arriving from the two slits are in the opposite phase, a dark pattern is formed
To cause destructive interference, the difference in the path between the two sources must be an odd multiple of the half wavelength.

Destructive interference

d \cdot s i n (θ) = (n + \frac{1}{2}) λ

$d\cdot sin(\theta )\,=\,(n+\frac {1 }{ 2} )\lambda$ (n = 0, 1, 2…)
position

y_{n} = \frac{(n + \frac{1}{2}) λ D}{d}

${y }_{ n }\, =\, \frac {\left( n+\frac {1 }{ 2} \right) \lambda D }{ d}$ (n = 0 , 1, 2…)

d: Slit spacing (m)
θ: diffraction angle (rad)
λ: wavelength of light (m)
D: Distance from slit to screen (m)

The ‘n’ value above is used to number dark patterns caused by destructive interference.