Waves
Diffraction
Interference
Conditions for Interference
Examples
Key Points
Definition
Superposition of two or more waves from coherent
Waves are Monochromic
Coherent Wave Sources
Constructive Interference
-When two waves reinforce to give increased amplitude at a point in space
Destructive interference
-When two waves cancel to give reduced (or zero) amplitude at a point on space
How to Achieve this?
Connect wave sources to the same signal generator
Divide waves using 2 slits
The extent of diffraction depends on the width of the gap compared with the wavelength of the waves
Diffraction is the spreading out of waves when they pass an obstacle
Path difference: (n+1/2) λ
Single Wavelength
Constant Frequency
Path difference: nλ
Young's Double Slit Experiment: λ=ax/D
Constant Phase Difference
Amplitude changes when wave is diffracted
Energy is dissipated when a wave is diffracted through a gap
DIFFRACTION GRATING
WORKED EXAMPLE
What is it?
A large number of equally spaced parallel slits and very closely spaced slits
If monochromatic light is incident on this plate, a pattern of bright fringes is produced
Has the same principle as double slit experiment but more than two slits being use
Formula
n(lambda) = dsin(teita)
n - number of order
lambda - wavelength
d - grating spacing
teita - angle
Application
Spectometers
Device that makes accurate measurements of lambda using a diffraction gating or prism