Waves Flashcards
Wave
A way in which energy is transferred from one place to another
Eg water ripples transfers kinetic energy
2 categories of waves
Transverse
Longitudinal
What type of wave is ripples on water?
Transverse
What defines a transverse wave?
If the oscillations are perpendicular to the direction of energy transfer
Transverse waves appearance
Oscillations (up and down)
Move in the direction the energy is being transferred
What defines longitudinal waves?
The oscillations are parallel to the direction of energy transfer
Longitudinal waves appearance
Upwards lines
Compressions = where particles are close together
Refractions = where they are spaced out
Oscillations move sideways
Transverse vs longitudinal waves
ALL types of Longitudinal waves require a medium to travel in like air, a solid or liquid
However not all transverse waves do
Examples of transverse waves
Light
Ripples on water
Examples of longitudinal waves
Sound
Do waves transfer matter?
NO JUST ENERGY!!!
so they do not move air particles if they travel through air
Or move water particles in water
They move on their OWN!!!!
How do transverse waves not transfer matter?
Because when the wave passes through, the particles just oscillate up and down not travelling through the medium
Because the oscillations perpendicular to the direction of energy transfer
How to longitudinal waves not transfer matter?
Because when the wave passes through, the particles just oscillate from side to side not travelling through the medium
Because the oscillations are parallel to direction of energy transfer
Amplitude
Maximum displacement of a point on a wave away from its undisturbed position
Aka the peak of the wave to the line
Wavelength
Distance from one point on one wave to the equivalent point on adjacent wave
This could be anywhere
How to measure longitudinal wavelength?
One compression to next compression
One refraction (not compression) to the next
Frequency
Number of waves passing a point each second
1 Hz = 1 wave per second
5 Hz = 5 waves per second
Frequency unit
Hertz Hz
Period
Time (in s) for one wave to pass a point
Period equation
1
———————
Frequency (Hz)
Wave speed
The speed at which the wave travels through the medium
And thus transfers energy
Wave equation
Wave speed (m/s) = frequency (Hz) x wavelength (m)
How can we find the speed at which a sound wave travels?
2 people stood a large distance apart
Person 1 clashes symbols to make a sound
Person 2 starts timing they see this happen using timer then stops when they hear it
Calculate speed = distance they stood apart/ time taken
What is the problem with using the cymbals/timer method to calculate wave speed?
People have different reaction times, it may take a different amount of time to press the timer depending on person
Time taken to see the person clash cymbals and hear it is incredibly short
How do we reduce the error with the cymbals/timer experiment?
Have multiple observers also using a timer
Take all these results, discard anomalies then calc mean
If the time is too short, increase the distance between both people
So longer distance = longer time to hear it so you can press it at the correct times
How does hearing work?
The sound waves hit the boundaries between 2 materials:
They are funnelled into the ear from the air
And hit the eardrum (thin membrane, solid)
Sound waves causes ear drum to vibrate
Causes sensation of sound for us
Normal human hearing frequency range
20Hz - 20,000Hz
What controls the human hearing range?
The frequency
Because the sound waves in air can trigger vibrations in solids but only for certain frequencies
Outside of that may not make eardrum vibrate
What happens if waves go from one medium to another?
Their speed can change
Ie speed travels faster in solids because particles are closer than gases so vibrations pass easier between them
Vibrations
Longitudinal sound waves causing air particles to move back and forth sideways
Or parallel to direction of travel
Passed along and causes sound
According to the wave equation, how do waves changing medium affect the wave speed?
If the wave passes from one medium to another it’s speed changes
Thus its wavelength changes
THE FREQUENCY DOES NOT CHANGE
Why does the frequency not change if a wave changes medium?
That would mean more or less waves pass a point in a specific second
Therefore they would have to be created at the boundary which isn’t possible
How can we view features of sound waves?
Connect a microphone to a cathode ray oscilloscope
Disadv of cathode ray oscilloscope
Represents sound waves as if they were transverse waves
But they are longitudinal
So dont get confused
What determines pitch of sound?
THE FREQUENCY
HIGH FREQUENCY so more waves = HIGH PITCH
LOW FREQUENCY so less waves = LOW PITCH
What determines the volume of a wave?
AMPLITUDE
SMALL AMPLITUDE so short and fat wave = QUIET
LARGE AMPLITUDE so long and thin wave = LOUD
Why can’t sound waves travel through a vacuum
Only move if the particles are vibrating side to side between each other
Thus no particles = no sound
How are sound waves reflected?
Reflected sound wave = Echo
Ultrasound
Sound waves with frequency high than upper limit of human hearing
So over 20,000
Pitch of waves depend on frequency therefore it’s very high pitched
What do ultrasound waves do at the boundary between different densities?
Partially reflect right back
Uses of ultrasounds
We can see the time it takes for the ultrasound to leave probe, bounce/ reflect off material and detected by probe, we can calc it’s distance away
And produce images eg for internal organs not surrounded by bone
Or detect defects in materials
Or distance from seabed in a ship
Why is ultrasound safer than x rays?
Doesn’t cause mutations so no risk of cancer
How can we determined distance using ultrasound
Distance (m) = speed (m/s) x time (s)
For total distance travelled, ie for it to be emitted then reflected up again
Therefore divide this by 2 solely for distance for emitted ultrasound
Interior of the Earth and its state
Crust, thin layer = solid
\/\/\/\/\/\/\/
Mantle = solid but can flow slowly
\/\/\/\/\/\/\/
Outer core = liquid
\/\/\/\/\/\/\/
Inner core = solid
How do scientists know the interior of the Earth if we have only dug a bit of the crust?
Using earthquakes
Movements between tectonic plates cause seismic waves
Carrying energy away from earthquake
Pass through Earth and detected by seismometers in different countries
Patterns of these waves give info on the interior of Earth
Types of seismic waves
P waves
S waves
P waves properties
Longitudinal
Pass through solids and liquids, but like all longitudinals not gases
Faster than S waves
S waves properties
Transverse waves
Only through solids
Travels slower than P waves
How to remember S waves properties?
Everything with S
tranSverSe wave
Only Solids
Slower Speed than P waves
S wave shadow zone
Zone where there are no S waves
That is because they can’t pass through liquid
What does the S wave shadow zone show scientists?
There must be a liquid core for the Earth because S waves can’t go through there
S waves patterns through Earth
Go through the mantle from where the earthquake was
But curve around the outer liquid core as they can’t pass through there
Creating S wave shadow zone
P wave patterns
Go through the mantle like S waves
But change direction and curve through the outer and inner core so they are through the middle
But leave areas where there are no P waves
= P wave shadow zone
What causes p wave shadow zone and what does it show?
P waves travel faster in solids than liquids
Because they refract when travelling through solid mantle, to the outer core
Then refract again when leaving
What shows the inner core is a solid?
Faint P waves In shadow P zones
Electromagnet wave
Transverse waves
That transfer energy from the source to what’s absorbing it (absorber)
Eg microwaves transfer energy from source (oven) to absorber (food)
Visible light through a prism
Splits to spectrum of colours
Colours in visible light
Red
Orange
Yellow
Green
Blue
Indigo
Violet
ROY G BIV
Frequency in colours
INCREASE as you go from RED ———> VIOLET
So red and orange have fewer waves per second and violet has more because it gets BIGGER as you go down
Wavelength from colours in visible light
DECREASE as you go from RED ———> VIOLET
so red has longer wavelength than violet because it decreases as you go down
How to remember the changes in colour spectrum?
RLLL
Red = low frequency = long wavelength = less energy
So opposite for the other side
Electromagnetic spectrum
🎶Radio waves
Microwaves
Infrared radiation
Visible light
Ultraviolet
X rays
Gamma rays 🎵
How does frequency change in the electromagnetic spectrum?
INCREASE from RADIO ———> GAMMA RAYS
So radio waves have less waves than gamma rays in one second because it increases
How does wavelength change in electromagnetic spectrum?
DECREASE from RADIO ———> GAMMA RAYS
so radio waves are longer/stretched out sideways than gamma rays because the wavelength decreases
How to remember properties of electromagnetic spectrum?
Just like colour spectrum
RLLL
Radio = Low frequency = Long wavelength = less energy
What is the part of electromagnetic spectrum visible to human eye?
Visible light the ONLYYYY
What type of spectrum is electromagnetic and why?
Continuos
The cut off point between one type and the other is not always clear
Can electromagnetic waves travel in a vacuum?
Yes because they are transverse waves which have the possibility to
How do electromagnetic waves travel in a vacuum?
All at the same speed
What speed do electromagnetic waves travel in a vacuum?
300 000 000m/s
Or 3 x 10^8 m/s
What happens to electromagnets based on their wavelengths?
What material transmits, reflects or absorbs them
Example of how microwaves act in terms of reflection, absorption or transmission
Microwaves are absorbed by food which cooks them
But reflected by metals
Examples of how visible light waves act in terms of different surfaces
Matt black = absorbed
Shiny metallic = reflected
What happens when electromagnetic waves are generated or absorbed?
Changes take place in atoms
Because in an atom, the electron moves up an energy level
It returns to its original one by generating an electromagnetic wave
Or
If a radioactive atom decays and gives off gamma ray
So it has less energy
