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Determining Wave Speed. Universal Wave Equation. Example – calculate wave speed. A harp string supports a wave with a wavelength of 2.3m and a frequency of 220.0 Hz. Calculate its wave speed. Example – calculate wavelength.

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determining wave speed
Determining Wave Speed
  • Universal Wave Equation
example calculate wave speed
Example – calculate wave speed

A harp string supports a wave with a wavelength of 2.3m and a frequency of 220.0 Hz. Calculate its wave speed

example calculate wavelength
Example – calculate wavelength
  • A trumpet produces a sound wave that is observed travelling at 350 m/s with a frequency of 1046.50 Hz. Calculate the wavelength of the sound wave.
factors that affect wave speed
Factors that affect wave speed
  • Temperature
  • Linear Density
reflection
Reflection
  • What will happen to the wave pulses shown below?
  • Link to video (blip.tv)

A: Wave pulse heading towards a wall.

B: Wave pulse heading towards a “free end”.

reflection transmission
Reflection & Transmission
  • When a wave moves from one medium to another, its speed changes but its frequency remains the same.
  • What else happens when waves move from one medium to another? What will happen to the pulses shown below?

B: Wave pulse travelling from a thicker rope into a thinner rope.(More Dense  Less Dense, Slower  Faster)

A: Wave pulse travelling from a thinner rope into a thicker rope.(Less Dense  More Medium, Faster  Slower)

interference of waves
Interference of Waves
  • Principle of Superposition:The resultant displacement is the sum of the displacements of each component wave.
interference of waves1
Interference of Waves
  • What happens after the waves interfere with each other?
interference of waves2
Interference of Waves
  • What happens when the wave pulses shown below meet?
  • Principle of Superposition:The resultant displacement is the sum of the displacements of each component wave.
interference of waves4
Interference of Waves
  • Constructive interference:Resultant displacement is greater than individual pulses.
  • Destructive interference:Resultant displacement is smaller than individual pulses.
standing waves
Standing Waves
  • When identical periodic waves travel in opposite directions, they produce a pattern that appears to be standing still. Such waves are known as standing waves.
  • Parts of a standing wave
  • Nodes
    • Points on wave that never move
    • Located half wavelength apart
  • Antinodes
    • Points that vibrate maximally
standing waves1
Standing Waves
  • The standing waves can be produced using one source:a 2nd identical wave is produced by reflection.
  • For every medium of fixed length, there are many natural frequencies that produce resonance:
standing waves2
Standing Waves
  • Fundamental frequency
    • Lowest natural frequency, longest wavelength
    • Also called fundamental mode
  • Overtones
    • Refer to all natural frequencies higher than the fundamental
    • 1st overtone = 1 node, etc.
  • Harmonics
    • Refer to fundamental & any overtone
    • Fundamental = 1st harmonic,1st overtone = 2nd harmonic, etc.
practice
Practice
  • P. 391 # 1-6
recap properties of waves
Recap: Properties of Waves
  • Reflection
  • Transmission
  • Require a medium in which to travel
  • Interference (Principle of Superposition)
    • Exhibit constructive & destructive interference

What are some other properties of waves?

law of reflection
Law of Reflection
  • The angle of incidence is equal to the angle of reflection:

A water wave incident on a barrier.

The dotted line is called the “normal”. The normal line by definition is perpendicular to the barrier.

All angles are measured from the normal.

refraction
Refraction
  • When waves travel from one medium into another, their speed changes.
  • This causes the wave to bend:

When water waves travel from deep to shallow water, the speed of the wave decreases.

Since the frequency of waves is constant, because the wave’s speed decreases, its wavelength decreases. (Why?)

Waves travelling from a faster to a slower medium always bend towards the normal.

diffraction
Diffraction
  • When waves travel past the edges of a barrier or through a small opening, waves bend & spread:
  • The amount of diffraction is greatest when the size of the opening is the approx. equal to the wavelength.
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