Waves

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# Waves - PowerPoint PPT Presentation

Waves. What are waves?. Wave –A disturbance that transfers energy through a medium without net motion of the medium. Mechanical Wave – a wave that propagates through a deformable, elastic medium Waves can be represented by a sine wave. Types of waves.

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## PowerPoint Slideshow about 'Waves' - kirkan

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Presentation Transcript

### Waves

What are waves?
• Wave –A disturbance that transfers energy through a medium without net motion of the medium.
• Mechanical Wave – a wave that propagates through a deformable, elastic medium
• Waves can be represented by a sine wave.
Types of waves
• Pulse wave – a single, non-periodic disturbance.
• Periodic or continuous wave – a wave whose source is some form of repeating motion.
Parts of a wave
• Crest – highest point above equilibrium.
• Trough – lowest point below equilibrium.
• Amplitude – maximum height of a crest or depth of a trough.
Parts of a wave
• Wavelength – the distance between two adjacent crests or troughs.
• Frequency – number of crests (or troughs) that pass by a point in a given amount of time.
• Period – Time for two adjacent crests to pass by a certain point.
Parts of a wave
• Wave velocity – velocity at which wave crests move.
• v = λf
• v = wave velocity
• λ = wavelength
• f = frequency
Speed of waves on cords
• v = √[T/(m/L)]
• v = velocity of a wave
• T = tension in cord
• m = mass of cord
• L = length of cord
Sample problem 1
• A wave whose wavelength is 0.30 m is traveling down a 300 m long wire whose total mass is 15 kg. If the wire is under a tension of 1000 N, what are the speed and frequency of this wave?
Types of Waves
• Waves can be categorized by how the medium moves in relation to the wave motion.
• Transverse wave – wave propagates perpendicular to the direction the medium vibrates.
• Examples – water waves, light, “the wave”
Types of Waves
• Longitudinal wave – the medium vibrates parallel to the direction of wave motion.
• Examples – sound, slinky waves
Wave Energy
• The amount of energy carried by a wave is proportional to the square of the amplitude.
• Intensity – power transported across unit area perpendicular to the direction of energy flow.
Wave Energy
• For a spherical wave,
• I = P/(4πr²)
• I = intensity (in W/m²)
• P = power
• r = distance from wave source.
Sample Problem 2
• The intensity of an earthquake P wave traveling through the Earth and detected 100 km from the source is 1.0 x 10⁶ W/m². What is the intensity of that wave if detected 400 km from the source?
Reflection
• Reflection is the bouncing of a wave off of a boundary.
• Transmission is when a wave is able to pass through a boundary.
Interference
• Interference is what happens when two waves pass through the same region of space at the same time.
• Where waves overlap, the resultant displacement is equal to the sum of their separate displacements.
Interference
• This is called the principle of superposition.
• Interference can be either constructive or destructive.
• Constructive interference – results when waves on the same side of equilibrium add together to form a larger displacement.
• Can be said to be “in phase”
Interference
• Destructive interference – results when waves on opposite sides of equilibrium combine to form a smaller displacement.
• Can be said to be “out of phase”
Standing Waves
• A standing wave is a wave that appears to only move up and down.
• Occurs when waves of a certain wavelength and frequency interfere with each other.
• Have nodes and antinodes.
Standing Waves
• Nodes are the part of a standing wave with no motion.
• Always has complete destructive interference.
• Antinodes are the part of a standing wave where the maximum amplitude occurs.
• Only spot where complete constructive interference occurs.
Standing Waves
• Only a certain set of frequencies will produce standing waves on a string.
• For a string, only frequencies where the length of the string is equal to a ½ multiple of the wavelength produce standing waves.
Standing Waves
• Fundamental frequency or 1st harmonic: L = ½λ₁
• First overtone or 2nd harmonic:
• L = λ₂
• Second overtone or 3rd harmonic:
• L = ³∕₂λ₃
Sample Problem 3
• A piano string is 1.10 m long and has a mass of 9.00 g. (a) How much tension must the string be under if it is to vibrate at a fundamental frequency of 131 Hz? (b) What are the frequencies of the first four harmonics?
Resonance
• When the external frequency of a vibration matches a resonant frequency of another object, the second object will start to vibrate.
• This is called resonance.
• Example: when you push a swing.