1. 4.5-Wave Properties

2. Snell’s Law

3. Snell’s Law

4. 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

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

6. 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

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

8. 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

9. Superposition and Interference • Wiki Sim – Huygens’ Principle of Superposition

10. 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

11. 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

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