P6 - Waves Flashcards
What are the two types of waves?
- *Longitudinal**
- *Transverse**
What are longitudinal waves?
Oscillations which are parallel to the direction of energy transfer. e.g. Sound waves.
They show areas of compression and rarefaction
Examples of longitudinal waves include: sound waves, ultrasound waves & seismic P-waves
What are transverse waves?
In tranverse waves oscillations are perpendicular to the transfer of energy.
The ripples on a water surfaces, vibrations in a guitar string, a Mexican wave , electromagnetic waves (- eg light waves, microwaves, radio wave), S-waves
What do waves do?
What do longitudinal waves require to travel?
All waves transfer energy from one place to another. e.g. sound transfers sound energy and ripples transfer kinetic energy.
In addition, all longitudinal require a medium to travel in e.g. Air,liquid and solid whereas not all tranverse waves require a medium.
For both waves the wave is always moving not the medium.
What is amplitude?
Amplitude
- Amplitude is defined as:
Amplitude is the maximum displacement of a point on a wave away from its undisturbed position.
- It is given the symbol A and is measured in metres (m)
What is Wavelength?
Wavelength distance covered by a full cycle of the wave, usually measured from peak to peak, or trough to trough
Amplitud
- Wavelength is defined as:
the distance from a point on one wave to the equivalent point on the adjacent wave.
- It is given the symbol A and is measured in metres (m)
What is a peak and trough?
- peak - the highest point above the rest position
- trough - the lowest point below the rest position
How do you measure wavelength for a longitudinal wave?
By measuring the distance between the compressions
What is the frequency?
Number of times a wave passes a point each second measured in Hertz(HZ)
What is a period and how do you calculate it?
Time for the wave to pass a point
period = 1/frequency
period, T, in seconds, s
frequency, f, in hertz, Hz
The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium.
What is wave speed
How do you calculate it?
The speed at which a wave moves through a medium
wave speed = frequency × wavelength
v = f λ
- *wave speed, v, in metres per second, m/s** frequency, f, in hertz, Hz
- *wavelength, λ, in metres, m**
What happens if wave is moving through the air and hits an object?
- Be transmitted or absorbed at the boundary between two different materials.
- Be reflected at the boundary between two different materials
- In certain cases waves can chage direction when it is passing through a material also known as rarefraction.
How do you measure speed of sound waves in the air?
- two people (person A and person B) are placed a distance apart, eg 100 metres
- person A fires a starter’s pistol
- person B or computer times the difference between seeing the flash of the gun and hearing the sound - this is measured in seconds
Or use camera or microphone
What can soundwaves do?
What is the range for human hearing and what happens outside that range?
Sound waves can trigger vibrations in solids but only over a limited range of frequency.
- *Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound. The conversion of sound waves to vibrations of solids works over a limited frequency range.(20Hz to 20,000Hz)**
- *This restricts the limits of human hearing as anything higher/lower than this may not be able to make the eardrum vibrate**
What happens when a wave travels into a medium?
Their wave speeds can change. When the wave speed changes as the waves pass from one medium to another, the wavelength also changes.
But the frequency does not change when the wave changes medium because waves would have to destroyed or created at the boundary which is impossible.
How can we view the feature of sound?
What does the higher the amplitude mean?
What is does it mean if the frequency is low?
You can view the features by connecting a microphone to cathode ray oscilloscope but it represents sound as transverse when it is longitudinal
Low frequencies = lower pitch
High amplitude = louder sound
What is ultrasound
How can we use ultrasound to calculate the distance between the probe and kidney?
- Ultrasound is defined as:
Sound waves with a frequency above the human hearing range of 20 000 Hz
- When meeting a boundary between two media ultrasound may be:
- Partially reflected
- Partially transmitted
- Partially absorbed
- The percentage that is reflected or transmitted depends on the two media at the boundary
- An air and glass boundary will have different percentages compared to an air and wall boundary
- The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is. This allows ultrasound waves to be used for both medical and industrial imaging.
They are much safer than x-rays as they do not cause mutation or increase risk of cancer & Is non-invasive
How do you determine the distance using ultrasound?
What is the structure of the inner earth?
Outside of the Earth is thin crust about 50m
Under that there is solid mantle
Then there is a liquid core.
Then there is a solid core
What are P waves:
-
P waves
These are longitudinal waves which pass through both solids and liquids at different speeds. They travel faster than S waves
The waves refract as they pass through the different layers of the Earth. This refraction affects the regions in which waves can be detected, yielding important information about the nature and size of the Earth’s various layers.
Refractions between layers cause two shadow zones, where no P-waves are detected, this suggests The inner core is solid – this is due the fact that P waves travel faster in solids than liquid so they slow down when the enter the liquid outer core causing them to refract which confirms the outer core is liquid.
Sometimes faint p-waves are detected in the shadow zone which show that the Earth contains a solid core.
What are S waves?
- S waves
- *S waves are transverse and can only travel through solids.**
In earthquakes because S waves cannot travel through liquids there is an S-wave shadow zone on the opposite side of the earth.
This tells scientists that the earth has a liquid core.
What happens when waves change direction?
Waves can change direction when they change speed, moving one medium to another.
When light enters glass, the velocity of the light changes which means the direction of the light also changes. The light ray bends towards the normal and the light ray is refracted.
The exact opposite happens when light leaves the glass and bends away from the normal.
How does Refraction work and what does change of direction depend on?
- Refraction occurs when light passes a boundary between two different transparent media
- At the boundary, the rays of light undergo a change in direction
- The direction is taken as the angle from a hypothetical line called the normal
- This line is perpendicular to the surface of the boundaries and is usually represented by a straight dashed or dotted line
- The change in direction depends on which media the light rays pass between:
- From less dense to more dense (e.g air to glass), light bends towards the normal
- From more dense to less dense (e.g. glass to air), light bends away from the normal
- When passing along the normal (perpendicular) the light does not bend at all
- The change in direction occurs due to the change in speed when travelling in different substances
- When light passes into a denser substance the rays will slow down, hence they bend towards the normal
- The only properties that change during refraction are speed and wavelength – the frequency of waves does not change
How do you record the magnitude of an earthquake?
Seismic Waves
- These waves pass through the Earth’s centre and can be detected at various points around the Earth using seismometers
- By carefully timing the arrival of the waves at each point, the location of the earthquake, along with its magnitude, can be pinpointed
Why are s and p waves important?
Discoveries from Seismic Waves
- The interior of the Earth is not directly observable as it is not physically possible to drill that far
How is Ultrasound used in Industry?
Ultrasound in Industry
- In industry, ultrasound can be used to:
- Check for cracks inside metal objects
- Generate images beneath surfaces
- A crack in a metal block will cause some waves to reflect earlier than the rest, so will show up as pulses on an oscilloscope trace
- Each pulse represents each time the wave crosses a boundary
- The speed of the waves is constant, so measuring the time between emission and detection can allow the distance from the source to be calculated
Compare Transverse waves to longitudinal waves
