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Waves
Contents
Characteristics of waves
 Types of wave
 Electromagnetic Spectrum
 The 7 Electromagnetic Waves
 Uses of Electromagnetic Waves
 Sound Waves
 Sound Quiz
 Ultrasound
 Seismic Waves
 Colliding: The Andes
 Spreading: Mid-Atlantic Ridge
 Sliding Past Each Other: San Francisco

Characteristics of Waves

Amplitude, a
The distance from the middle
to either the trough or peak

Wavelength, λ (metres)
The distance of one full cycle
of a wave

Frequency, f (Hertz, Hz)
The number of waves that pass
a point in 1 second
Waves carry energy from one place to another
Types of Wave

Transverse
(light, water, strings)
Vibrations are at 90° to the direction of wave travel

Longitudinal
(sound, slinky spring)
Vibrations are along the same direction as wave travel
Electromagnetic Spectrum

Electromagnetic waves travel at the speed of light in a vacuum

The electromagnetic spectrum consists of 7 types of em wave:
The 7 Electromagnetic Waves
Short
wavelength
Long
wavelength
High
frequency
Low
frequency
Uses of Electromagnetic Waves

Wavelength of the EM spectrum continually changes
high frequency = short wavelength
high frequency = high energy
high energy = more dangerous

Radio Waves (communications)
TV and FM radio (short wavelength)
Direct line of sight with transmitter (do not diffract)
Medium wavelength – travel further because they reflect
from layers in the atmosphere
Uses of Electromagnetic Waves

Microwaves (cooking and satellite signals)
Satellite signals: Frequency of microwaves pass easily
through atmosphere and clouds
Cooking: microwaves are absorbed by water molecules.
These water molecules become heated  heat food
Dangers: microwaves are absorbed by living tissue
Internal heating will damage or kill cells
Uses of Electromagnetic Waves

Infrared Radiation (remote controls, toasters)
Any object that radiates heat radiates IR radiation
IR is absorbed by all materials and causes heating
IR is used for night vision and security cameras as IR is
visible in daytime or night-time
Police use it to catch criminals, army use it to detect enemy
Dangers: damage to cells (burns)
Uses of Electromagnetic Waves

Ultraviolet (detect forged bank notes, tanning booths)
Darker skin protects UV from penetrating skin tissue deeper
under the skin
Forged bank notes fluoresce in UV light; real don’t
Dangers: overexposure damages surface cells and eyes
Uses of Electromagnetic Waves

X Rays (detect bone breaks)
X-rays pass through flesh but not dense material like bones
Dangers: X-rays damage cells and cause cancers
Radiographer precautions include wearing lead aprons and
standing behind a lead screen to minimise exposure

Gamma Rays (cause and treat cancers)
In high doses, gamma can kill normal cells and cause cancers
Gamma can be used to kill mutated cells though too…
Sound Waves

How do we hear?
Object vibrates  vibrations travel away as a wave
Vibrations enter the ear and vibrate
a liquid in the inner ear
Vibrating liquid affects 1000s of nerves which tell your brain
that you can hear a sound
Amplitude (dB) (loudness)
amplitude
Wavelength (m)
amplitude
Frequency/Pitch (High or Low)
amplitude
Wavelength (m)
amplitude
Wavelength (m)
Wavelength (m)
Sound Quiz
The Greek letter  refers to which part of a wave?
The distance between two crests of a wave is called the…?
Frequency is measured in…?
If the amplitude of a sound wave increases,
what would you hear?
What is the unit of amplitude of a sound wave?
Does sound travel through space?
Increasing the pitch also increases what?
If the amplitude of a light wave increases, what would you see?
Which has the highest pitch – a wave with
short wavelength or long wavelength?
Two people at equal distances from a sound source. One
is under water, the other is standing on the ground. Who
will hear it first?
Ultrasound
Ultrasound: sound with very high frequency
: frequency above 20kHz - inaudible
: high frequency = short wavelength
V=fxλ
V = wave speed (m/s)
f = frequency (Hz)
λ = wavelength (m)
Wavelength, λ (m)
The 4 Uses
1. Industrial Cleaning
Ultrasound can be used to clean delicate equipment.
Short λ = narrow, focused beam.
Vibrations remove dirt effectively by “shaking” dirt loose.
No need to dismantle the equipment.
The 4 Uses
2. Industrial Quality Control
Ultrasound waves can detect cracks inside metals.
When a sound wave travels from one substance to another,
some waves are reflected back as echoes.
The reflected waves (echoes) are
detected by a computer...
An echo = a flaw in the metal
 a crack has formed.
The 4 Uses
3. Pre-Natal Scanning
X-rays can be used to see inside the body - (unsafe for a baby)
Ultrasound can create images and is safer.
Passes through new substance (skin, muscle, bone)
 waves are reflected as echoes.
The reflected waves (echoes) are
detected by a computer...
which builds up a
picture from each
echo.
The 4 Uses
4. SONAR - Direction and Range
• Bats produce ultrasound squeaks
 pick up the reflections using their big ears.
• Brain processes the reflected signals into
a mental picture of the surroundings.
• Ships use SONAR to detect items on
the seabed.
• The pattern of the reflections
indicates the depth and shapes.
Seismic Waves
P waves (primary):
1) They are longitudinal so they cause the ground to move up
and down
2) They pass through solids and liquids
3) They go faster through more dense material
S waves (secondary):
1) They are transverse so they cause the ground to move
sideways
2) They ONLY pass through solids
(hint: s wave = solids)
3) They go faster through more dense material
Seismic Waves
S waves will only travel
through a solid
P waves travel through
the Earth and are
refracted when they
pass through a medium
The paths of these
waves are curved
because density is
gradually changing
Observations: 1) It has a thin crust, 2) it has a semi-fluid
mantle where density increases with depth, 3) a core with a
liquid outer part and a solid inner part
Tectonics

The Earth’s crust is made up of plates of rock like a jigsaw

These plates move slowly as they float on the liquid mantle

This mantle moves slowly by convection currents, caused by
the radiation emitted from the Earth’s core

The Earth’s crust is constructed of sedimentary rock layers

These plates meet at boundaries…
… at which plates collide, separate or slide past each other

Earth’s Crust
Sedimentary rocks
settle in layers
The oldest rock is
at the bottom; the
newest at the top
Sedimentary rock is often folded or fractured due to pressures:
Colliding: The Andes

Oceanic plates are more dense than continental plates

When they collide:
oceanic plate is pushed under  earthquake
continental plate slides over and crumples  mountains
Oceanic plate melts  increased pressure of magma
pushes through the crust as a volcano
Spreading: Mid-Atlantic Ridge

As tectonic plates move apart, magma rises and sometimes
with enough force to produce an underwater volcano


Force causes tidal waves  tsunamis
These cause huge destruction when they reach the land

As the magma rises and cools, underwater mountains form

Evidence for Continental Drift e.g. Atlantic Ocean
Sliding Past Each Other: San Francisco

Plates can slide past each other

But when they do, they catch on each other and lurch

This lurch lasts a few seconds but is extremely violent

Violent shaking destroys buildings

Poorer countries suffer worse as they have:
1) overcrowded cities
2) poorly constructed buildings
3) inadequate rescue services
Summary
Parts of a wave; transverse (light) and longitudinal (sound)
 EM spectrum: radio, microwaves, IR, UV, X-ray, Gamma
 Ultrasound has 4 uses
 Seismic waves: P (quicker) and S (solid only) waves
 Tectonics drift on molten mantle and meet at boundaries
 Interaction causes:
1) earthquakes
2) volcanoes
3) mountains
4) trenches
5) ridges
6) evidence for Continental Drift
