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Waves

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What is a Wave? "A wave can be described as a disturbance that travels through a medium from one location to another location ."

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**Transverse Wave Motion**

A group of people jumps up and sits back down, some nearby people see them and they jump up, some people further away follow suit and pretty soon you have a wave travelling around the stadium. The wave is the disturbance (people jumping up and sitting back down), and it travels around the stadium. However, none of the individual people the stadium are carried around with the wave as it travels - they all remain at their seats

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Transverse wave In a transverse wave the particle displacement is perpendicular to the direction of wave propagation The particles do not move along with the wave; they simply oscillate up and down about their individual equilibrium positions as the wave passes by . Light waves are transverse in nature.

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**Transverse wave Transverse waves on a string**

The string is displaced up and down as the wave travels from left to right, but the string itself does not experience any net motion.

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**RIGHT ANGLES TO WAVE DIRECTION**

TRANSVERSE WAVE vibrations WAVE DIRECTION VIBRATIONS ARE AT 90O OR RIGHT ANGLES TO WAVE DIRECTION

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longitudinal wave In a longitudinal wave the particle displacement is parallel to the direction of wave propagation The particles do not move down the tube with the wave; they simply oscillate back and forth about their individual equilibrium positions. Pick a single particle and watch its motion Sound waves are longitudinal

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**VIBRATIONS ARE PARALLEL**

LONGITUDINAL WAVE vibrations WAVE DIRECTION VIBRATIONS ARE PARALLEL TO WAVE DIRECTION

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Parts of a wave The crest of a wave is the point on the medium which exhibits the maximum amount of positive or upwards displacement from the rest position The trough of a wave is the point on the medium which exhibits the maximum amount of negative or downwards displacement from the rest position.

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Amplitude The amplitude of a wave refers to the maximum amount of displacement of a particle on the medium from its rest position.

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Wavelength The wavelength of a wave is the distance between any two adjacent corresponding locations on the wave train. This distance is usually measured in one of three ways: crest to next crest, trough to next trough, or from the start of a wave cycle to the next starting point.

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**All waves are caused by vibrations**

Diagram of a wave All waves are caused by vibrations PEAK OR CREST WAVELENGTH AMPLITUDE TROUGH WAVELENGTH

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**Frequency and Time period**

The frequency (f) of a wave is the number of cycles that pass the observer in a given time. Hertz is the unit of frequency. Frequency and period are exact inverses of each other, f = 1 / T or T = 1 / f

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**Finding the relationship between WAVESPEED, FREQUENCY & WAVELENGTH**

10m Frequency = 4Hz What is the relationship? Wavelength = 5 m Wavespeed = 20 m/s

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**WS F x WL WS = F x WL F = WS WL WL = WS F**

wave speed (m/s) = frequency (Hz) x wavelength (m) WS = F x WL F = WS WL WL = WS F WS F x WL

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Wave Equation The relation between the speed (v) of a wave ,its wavelength (λ) and frequency (f) is given by Speed = Wavelength x Frequency Using the symbols v, λ , and f, the equation can be rewritten as v = f x λ

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**1. If the speed of a wave is 340m/s, and its wavelength is 20m, what is its frequency?**

wave speed = frequency x wavelength 340 = frequency x 20 frequency = = 17 Hz 20

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**If 300 cycles are produced in 60s and the wavelength is 10m, find:-**

(a) the frequency 300 cycles 60s (b) the wave speed wave speed = frequency x wavelength = 5 cycles/s = 5 Hz = 5 x 10 = 50 m/s

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**Light waves travel at 300 000 000 m/s**

Light waves travel at m/s. If their frequency is 500Hz, find their wavelength wave speed = frequency x wavelength = x wavelength = 500 m

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**If 25 cycles occur in 1 second and their wavelength is 3 metres, find the wave speed**

wave speed = frequency x wavelength = x 3 = m/s

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**WAVEFRONTS PEAK/CREST WAVELENGTH**

WAVEFRONTS (PEAK/CREST OF WAVES FROM ABOVE)

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**Each line is a peak/crest of a circular wave**

Circular Wavefronts Each line is a peak/crest of a circular wave

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Diffraction of Waves Diffraction means spreading out. This can occur to waves when they go through a small gap.

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**Peaks or Crests of Waves**

Diffraction (spreading out) of waves through a gap equal or smaller than the wavelength Spreading out Peaks or Crests of Waves

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**Small amount of spreading out Peaks or Crests of Waves**

Diffraction (spreading out) of waves through a gap larger than the wavelength Small amount of spreading out Peaks or Crests of Waves

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CONSTRUCTIVE INTERFERENCE Wave A Wave B Output

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INTERFERENCE DESTRUCTIVE Wave A Wave B Output

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Interference of Waves Wave A Wave B Resultant Wave

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**Constructive Interference**

Interference of overlapping waves Peak meets Peak or Trough meets Trough Constructive Interference

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**Destructive Interference**

Interference of overlapping waves Peak meets Trough Destructive Interference

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**Hope you enjoyed Learning**

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Chapter 20 Waves.

Chapter 20 Waves.

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