# Waves

Waves

Celtic Harp

Irish folk tunes

arranged by

Howard Baer

Propagation of

Waves

Key Terms

★Reflection

★Refraction

★Absorption

Diffraction

Diffraction is

significant only when

D ≤ λ

Interference

★Interference occurs

whenever two waves

occupy the same space

at the same time.

Resultant Wave

★The combined wave

formed by the superposition

of two individual

waves

Constructive Interference

★The two interfering waves

reinforce one another

★Occurs when the two waves

are in phase

Constructive Interference

Destructive Interference

Destructive Interference

★The two interfering waves

cancel one another

★Occurs when the two waves

are out of phase

Video I-3

Interference: Transverse

Waves on a String.

Constructive Interference –

Waves

2

1.5

1

0.5

0

-0.5

-1

-1.5

-2

Destructive Interference –

Waves

1

0.5

0

-0.5

-1

Constructive Interference

(unequal amplitudes)

2

1.5

1

0.5

0

-0.5

-1

-1.5

-2

Destructive Interference

(unequal amplitudes)

1

0.5

0

-0.5

-1

Sound From Two Sources

Sound From Two Sources

★Constructive interference

occurs when

L 1 - L 2 = n λ

Sound From Two Sources

★Destructive interference

occurs when

L 1 - L 2 = (n+ ½)λ

Video II-5

Interference of Sound Waves

Beats

★Occur when two waves of

slightly different

frequency interfere

Beats

1

0.5

0

-0.5

-1

2.5

2

1.5

1

0.5

0

-0.5

-1

-1.5

-2

Video II-6

Beats

Beat Frequency

f beat = |f 1 -f 2 |

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