4.5-Wave Properties

Snell’s Law

Snell’s Law

Snell’s Law - Definition It is the ratio of the velocity of the wave in the two media Or the ratio of the sine of the angle of incidence to the sine of refraction REMEMBER – because it is a ratio, this means the refractive index is a DIMENSIONLESS QUANTITY

Diffraction When waves pass through apertures or around obstacles they tend to spread out. This spreading out is called DIFFRACTION.

Maximum Diffraction Maximum diffraction will occur when the gap or obstacle size is close to the wavelength of the wave. http://www.acoustics.salford.ac.uk/feschools/waves/diffract3. php

Phase and Phase Difference This is a measure of how “in step” the different waves (or particles) are.

Phase Difference If the particles are moving together we say they are “in phase” If the particles are “out of phase” by a half cycle they are π radians out of phase. A phase difference of π/2 radians shows they are out of phase by ¼ of a cycle

Superposition and Interference Wiki Sim – Huygens’ Principle of Superposition

Huygens Principle of Superposition The displacement of any point due to the superposition of wave systems is equal to the sum of the displacements of the individual waves at that point

Conditions for Interference Constructive Interference Phase difference = 2nπ radians (the waves are in phase) Path difference = nλ (on the data booklet) Destructive Interference Phase difference = π(2n+1) Path difference = (n+ ½) λ

Phase and Path Difference If the path difference is d and the phase angle is θ. Then θ= 2πd/λ