Waves Interaction Interaction of waves with matter Absorption

Waves – Interaction

$Interaction of waves with matter Absorption Reflection/refraction occur at interfaces between different materials Diffraction$

Interaction of waves with matter Absorption Reflection/refraction occur at interfaces between different materials Diffraction And all occur simultaneously Refraction

Propagation of waves • Water waves propagate along surfaces that are continuous. § A water wave can not spread across a discontinuous surface.

• Occurs when a wave “bounces” off a barrier • Examples – Echoes – Light reflection of the sun off the Moon

Optical Fibers • Plastic or glass light pipes • Applications: – Medicine: endoscope (light can be directed even if bent and the surgeon can view areas in the body using a camera. ) – Telecommunications The cladding has a lower n than the core

Reflection The return of a wave back to its original medium is called reflection. Fasten a spring to a wall and send a pulse along the spring’s length. The wall is a very rigid medium compared with the spring, so all the wave energy is reflected back along the spring. Waves that travel along the spring are almost totally reflected at the wall.

Diffuse Reflection Diffuse reflection allows us to see most things around us. a. Light is diffusely reflected from paper in many directions. b. Light incident on a smooth mirror is only reflected in one direction.

$Refraction • The bending of a wave as it passes at an angle from$

Refraction • The bending of a wave as it passes at an angle from one medium to another. • Example – looking into water. • As a wave travels from one medium into another its speed will change based on the density of the medium and causes the wave to bend

$Refraction? Spear fishing has been used for centuries and is still practiced by subsistence$

Refraction? Spear fishing has been used for centuries and is still practiced by subsistence communities. To accurately spear the fish, fishermen learn to aim a short distance behind the fish’s image, in order to compensate for the effect of refraction.

$Diffraction • Bending of waves around a barrier or through an opening • Depends$

Diffraction • Bending of waves around a barrier or through an opening • Depends on wavelength & size of barrier or opening Go to this website: http: //phet. colorado. edu/simulations/sims. php? sim=Wave_Interference ~Wave simulation / add slits in wall to get diffraction

14. 2 Waves and boundaries • Boundaries that are not straight can be used to change the shape of the wave fronts and therefore change the direction of a wave. • A sharp boundary creates strong reflections. • A soft boundary absorbs wave energy and produces little reflection.

Superposition and Interference Superposition - Overlapping waves add. Constructive interference = crest meets crest Destructive interference = crest meets trough Constructive Destructive

Basic Concept Two Source Pattern Constructive: Crest meets crest Trough meets trough Destructive: Crest meets trough

A B If the sources are in phase, will interfere constructively

A B If the sources are out of phase, will interfere destructively