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
Why can’t soundwaves pass through space
What is an Echo?
- Futhermore, soundwaves can only move through a medium as they can only move if particles are vibrating.
This is why they cannot passthrough a vaccum as there are no particles to vibrate.
- Soundwaves can be reflected. This in known as an echo.
• describe, with examples, processes which convert wave disturbances between sound waves and vibrations in solids.
soundwaces cause a glass to be shattered by an opera singer
OR
the effect of sound waves on the ear drum
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 Echosounding?
Echo sounding, using high frequency sound waves is used to detect objects in deep water and measure water depth.
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
How do scientists know the structure of the inner earth?
The answer is earthquakes.
An earthquake happens due to a sudden movement between the tectonic plates of the Earths crust.
This causes seismic waves which carry energy through the Earth. These seismic waves are detected by seismometers in different countries. The patterns give us information about the interior.
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.
