Waves Flashcards
What are waves?
Repeated vibrations of energy transfer
How is energy transferred?
By waves knocking neighbouring particles
What is a transverse wave?
Waves where points along the wave vibrate perpendicular to the direction of energy transfer
For a transverse wave
The energy transfer is in the same direction as the motion
They transfer energy but not particles of the medium
They move through liquids and solids but not gas
Some can travel through a medium (EM WAVES)
Examples of TRANSVERSE waves
- Ripples on the surface of the water
- Vibrations on a guitar string
- S waves
- EM waves
What are longitudinal waves?
Waves were the points along the wave vibrate parrallel to the direction of energy transfer
Properties of a longitudinal wave
- Energy transfer is in the same direction as motion
- Transfer energy but not particles of a medium
- CAN moves through liquids solids and gas
- They CANT travel through a vacuum as there are no particles
Examples of longitudinal waves
- Sound waves
- P waves
- Pressure waves
What is amplitude, wave length, wave frequency and time period?
Amplitude= Distance from the undisturbed position of the wave to the peak or trough - METRES
Wavelength= The distance from one point on a wave to the same point on the next wave - METRES (Symbol is lambada)
Wave frequency= The amount of waves that pass a point in one second - HERTZ
Time period= The time take for one wave to pass a point - SECONDS
Equation for wave speed
Wave speed = Frequency x Time
What do transverse waves have?
Peaks and troughs
What do longitudinal waves have?
Rarefactions and compressions
How are sounds waves transmitted?
Longitudinal waves work by the molecules vibrating and knocking into vibrating particles/molecules.
The more molecules that are present the more faster the wave can transfer energy
In what medium do sound waves travel fastest?
In solids and slowest in gases
Refraction of sound
When sound waves travel from a denser medium to a less dense medium their:
Wavelength increases
Frequency stays the same
Velocity increases
What is reflection?
When a wave hits a boundry between two media and doesnt pass through
Rule for the angles of incidence and reflection?
The angle of incidence=angle of reflection
Reflection on flat surfaces
Flat surfaces are much smoother so the stronger the reflected ray
Reflection on rough surfaces
Least reflective, because the light scatters in all direction
What do opaque surfaces reflect?
Opaque surfaces reflect the light that isnt absorbed by the material
The electrons will absorb the light energy then reemit it as a reflective wave
What is transmission?
When a wave passes through a substance
What happens when a wave is transmitted through a material?
It is partially absorbed so the transmitted wave has a smaller amplitude
What is absorbtion?
When the energy is transferred from the wave to the particles of a substance
Waves can be partially or completely absorbed
When will light be absorbed by a material?
When the frequency of the wave matches the levels of the electrons
How do sound waves travel through solids
Sound waves are vibrations of air particles
When a sound wave comes in contact with a solid, these vibrating air particles are transferred to the solid
The compressions and rarefactions cause changes in pressure so sound waves are a type of pressure wave
How do sound waves in ears transfer sound?
The sound wave travels down the auditory canal towards the ear drum
The pressure of the sound wave exerts a force on the eardrum which causes the ear drum to vibrate
The ear drums vibrations are transferred onto 3 small bones which then transfers vibrations into the inner ear
The inner ear nerve cells detect the sound and transfer electrical signals to the brain
What frequency do humans hear at?
20Hz - 20,000Hz
What is ultrasound?
Sound waves with a frequency of greater than 20,000Hz
What is infrasound?
Sound waves with a frequency less than 20Hz
What may happen to ultrasound when meeting a boundary between two media?
May be partially reflected, transmitted or absorbed
When is the greatest percentage of the wave reflected between media?
When the difference in the speeds in the media is large
What is echo sounding? What does it use? And what does it show?
Echo sounding is a sound wave which uses ultrasound to detect the depth of the ocean.
The time it takes for the wave to return determines the depth
How is ultrasound used in medicine?
To construct images of a foetus
To generate images of internal organs
As a medical treatment to remove kidney stones
What is an ultrasound detector made of
A tranduscer which detects and producers a beam of ultrasound
How does an ultrasound work
The ultrasound waves are reflected back to the tranduscer by boundries between tissues in the path of the beam
When these echoes hit the tranduscers they generate electrical signals that are sent to the ultrasound scanner to build an image
Is ultrasound harmful?
No it is believed to be harmless and non-invasive
How are ultrasounds used in industry?
A crack in a metal will cause some kind of bump on the oscilliscope as the wave is reflected back earlier than the rest
What waves do earthquakes produce?
P-Waves (primary waves)
S-Waves (secondary waves)
How are earthquake waves detected?
Using a seisometer
P wave properties
Longitudinal waves Can pass through solids and liquids Faster than s waves They are low infrasound waves Only refract when pass through different layers of the earth
S wave properties
Transverse waves
Cant move through liquids only solids
Slower than P waves
What do seismic waves show?
Only P waves are detected on opposite sides of the earth so the mantle is solid as both waves can pass through it but the outercore is liquid
The inner core is solid due to the size and positions of the shadow zones created by p waves.
