Waves

Menu Describing Waves Ultrasound Refraction of water waves Seismic Waves

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

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

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

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

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

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

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

Our Ears can only hear a certain range of ‘frequencies’ The ‘NORMAL’ range of human hearing is:- 20 Hz to 20,000Hz 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

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

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

Foetal Scanning Can you see the baby sucking its thumb? Menu

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 Return to Menu

Refraction of water waves

Deep Water - Fast Waves Shallow Water - Slow Waves

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

Refraction – of plane waves Deep water Boundary Shallow water

Deep Deep Shallow

Deep Deep Shallow If the waves arrive perpendicular to the boundary they do not bend Menu

The Structure of the Earth Seismic Waves & The Structure of the Earth

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

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

The Structure of the Earth Crust Mantle Outer Core Inner Core

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

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

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

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

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

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 Return to Menu