Today
We will prove that light acts
like a wave, again. This time
we will shine our laser on 2
closely spaced slits.
E
Let’s assume that
they are very narrow,
so that the single slit
interference pattern
is not noticeable.
Huygen’s Principle
The narrow double slits act
like 2 distinct point sources of
waves. We will again get an
interference pattern
Lets look more carefully…
How does the interference pattern emerge?
Constructive Interference
Destructive Interference
Dark and bright spots
alternate
The Math…
Light from S2 has to travel farther than light from S1.
The path difference is δ=d sinθ.
Constructive interference occurs at point P if δ =0,
or if δ is a multiple of the wavelength λ.
Æ d sinθ = mλ, m=0, ±1, ±2, ±3,…
Double Slit Interference
• The rings
cross at some
places, giving
extra
amplitude to
the wave
• A pattern of
bright and dark
spots emerge
Double Slit Interference
• Amazingly, light is not the only thing that acts as both a
wave and a particle.
• Everything is both a wave and a particle.
Click to play a simulation
of a quantum particle –
like an electron – passing
through 2 slits. Particles
also act as waves.
Performed by Dr. K.
Michielsen and Prof. dr.
H. De Raedt
Diffraction Grating
Thin Films
Color = wave length