Chapter 11.3. Reflection Reflection occurs when an object or a wave hits a surface through which it cannot pass, and it bounces back Examples: Shouting.

Chapter 11.3

ReflectionReflection occurs when an object or a wave

hits a surface through which it cannot pass, and it bounces backExamples:

Shouting in an empty gym Looking in a mirror

The law of reflection: the angle of incidence equals the angle of reflection

The Law of Reflection

• Angle of reflection= Angle of incidence

Free end and Fixed end reflection

Refraction• The bending of waves

due to changes in speed is called refraction

• Refraction occurs when a wave enters a new medium at angle, one side of the wave changes speed before the other side, causing the wave to bend

• Bending occurs because the two sides of the wave are traveling at different speeds

• Examples:– Seeing a rainbow– Trying to grab an

object underwater

What are the two mediums the straw has entered?

DiffractionDiffraction occurs when a wave bends around

a barrier or passes through an opening in a barrier, it bends and spreads out

Interference

Two waves can overlap when they meetInterference is the interaction between waves

when they meetThere are two types of Interference

1. Constructive Interference2. Destructive Interference

Constructive Interference• Constructive Interference

occurs when waves combine to make a wave with a larger amplitude

• When crests from each wave meet, constructive interference makes a higher crest in the area of overlap– The amplitude of this

crest is the sum of the amplitude of the two original crests

• After the waves pass through each other they continue on as if they had never met

Destructive Interference• Destructive Interference

occurs when two waves combine to make a wave with a smaller amplitude

• Can be thought of as subtracting energies

• Destructive interference occurs when the crest of one wave overlaps the trough of another wave– If the crest has a larger

amplitude than the trough, the crest wins and part of it remains

– If the original trough has the larger amplitude the result is a trough

– If the original waves have equal amplitudes then the crest and trough completely cancel out

Standing Waves• Occurs when an

incoming wave and reflected wave have just the right frequency, and they produce a wave that appears to be standing still

• A standing wave appears to be standing in one place, but in reality it is really two waves interfering as they pass

Nodes and AntinodesNodes are points of

zero amplitude produced by destructive interference of standing wavesNodes are always

evenly spaced along a wave

Antinodes are points of maximum amplitude on a standing wave created by constructive interferenceAntinodes are also the

points of maximum energy on the wave

Antinodes occur halfway between nodes

Resonance• Most objects have at

least one natural frequency of vibration

• If a nearby object vibrates at the same frequency it can cause resonance

• Resonance is an increase in the amplitude of a vibration that occurs when external vibrations match an object’s natural frequency

• Resonance can be useful– Example: musical

instruments use resonance to produce stronger, clearer sounds

• Resonance can be harmful– Earthquakes (Mexico

City Earthquake of 1985)