1. Waves

2. Menu Describing Waves Ultrasound Refraction of water waves
Seismic Waves

3. Longitudinal Waves SOUND IS A LONGITUDINAL WAVE
Direction of wave Travel
Vibrations
In Longitudinal waves the VIBRATIONS are along the SAME DIRECTION as the Wave is Travelling
SOUND IS A LONGITUDINAL WAVE

4. Transverse Waves Most Waves are Transverse. LIGHT IS A TRANSVERSE WAVE
Direction of Wave Travel
Most Waves are Transverse. LIGHT IS A TRANSVERSE WAVE
Vibrations are at right Angles to Direction of Travel

5. Describing Waves
Vertical
displacement
Amplitude
Horizontal
Displacement
Amplitude
THE AMPLITUDE shows the displacement of the particles. It is related to energy

6. Describing Waves THE WAVELENGTH is a full cycle of the wave Wavelength
Vertical
displacement
Wavelength
Horizontal
Displacement
THE WAVELENGTH is a full cycle of the wave

7. Describing Waves
Vertical
displacement
Time
THE PERIOD is the time taken for 1 complete cycle. (Notice the change in the horizontal axis)

8. Frequency
The frequency is the number of waves that pass a set point each second
It is measured in hertz (Hz)

9. The Wave Equation
Speed Frequency & Wavelength are all linked together using the following equation:-
SPEED = FREQUENCY x WAVELENGTH
m/s Hz m

10. Our Ears can only hear a certain range of ‘frequencies’
The ‘NORMAL’ range of human hearing is:-
20 Hz to ,000Hz
A wasp moves its wings more than 20 times a second because we can hear it
This means that we can only hear objects that vibrate over 20 times per second

11. The upper limit decreases with age
The upper limit decreases with age. Sounds above 20,000Hz can’t be heard by humans. They can however be heard by dogs, bats etc
Sounds above 20,000Hz are called ULTRASOUND

12. Ultrasound is useful to us
We can use ultrasound to:-
Clean delicate mechanisms (electronics, teeth & jewellery)
Check for ‘cracks’ in aeroplane wings
Sonar and
Pre- natal Scanning

13. Foetal Scanning
Can you see the baby sucking its thumb?
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14. When sound is reflected we call it an ECHO
We can use sound echoes to detect:
shoals of fish
Oil reserves
how a foetus is developing inside the mothers womb
cracks on aeroplane wings/ bridges
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15. Refraction of water waves

16. Deep Water - Fast Waves
Shallow Water - Slow Waves

17. Waves are bent towards the normal
Wavelength decreases
Frequency stays the same
Deep Water - Fast Waves
Shallow Water - Slow Waves

18. Refraction – of plane waves
Deep water
Boundary
Shallow water

19. Deep
Deep
Shallow

20. Deep
Deep
Shallow
If the waves arrive perpendicular to the boundary they do not bend
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21. The Structure of the Earth
Seismic Waves
&
The Structure of the Earth

22. The Earth’s Crust Is Made up of ‘Plates’ That Constantly Move
Which way have the ‘plates’ moved?

23. An Earthquake Occurs When There Is Movement in the Plates
There are 2 types of waves
P WAVES are Push and Pull Longitudinal Waves
S WAVES are Shear or Shake Transverse Waves

24. The Structure of the Earth
Crust
Mantle
Outer Core
Inner Core

25. The Structure of the Earth
The paths of the waves are curved because of Refraction (changes in density)
If the wave travels along the ‘normal’ it does not deviate from its position

26. The Structure of the Earth
P waves travel through both solids & liquids
P waves travel faster than s waves
NO WAVES pass through the Shadow Zone
No S Waves reach here as they can’t pass through the core

27. What does the seismograph tell us about the structure of the Earth?
1) About halfway through the Earth there is an abrupt change in direction of both types of waves, indicating a sudden change in density at that point – THE CORE

28. What Does the Seismograph Tell Us About the Structure of the Earth?
2) The fact that S waves are NOT detected in the shadow of the core tells us that the CORE IS LIQUID

29. What Does the Seismograph Tell Us About the Structure of the Earth?
3) P Waves travel slightly faster through the middle of the core. This strongly suggests there is a SOLID INNER CORE

30. What damage can earthquakes do?
Damage to buildings
Fires caused by ruptured power lines
Death
Disease can spread rapidly due to disrupted water & food supplies
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