waves Flashcards
what do waves do?
they transfer energy from one place to another but not matter
what are transverse waves?
waves whose oscillations are perpendicular to the direction of the wave
what are examples of transverse waves?
- electromagnetic waves
- ripples on water
- waves on a string
what are longitudinal waves?
waves whose oscillations are parallel to the direction of the wave
what are examples of longitudinal waves?
- sound waves
- seismic waves
what is frequency?
number of waves passing a point each second
what is a period?
the time for one complete wave
what is the equation for a period?
T = 1/f
what is the speed of light?
3 × 10⁸ m/s
what can happen when waves arrive at a boundary between two different materials?
- absorption
- reflection
- transmission (refraction)
what is the rule for all reflected waves?
the angle of incidence = angle of reflection
when does specular reflection occur?
when waves are reflected in a single direction and the boundary is smooth
when does diffuse reflection occur?
when waves reflected in multiple directions and the boundary is rough
what occurs during refraction?
a wave crosses a boundary and changes direction
what affects the speed of a wave passing through a material?
the material’s density
when does a wave bend towards the normal when passing through a material?
when the material has a higher density and the wave slows down
when does a wave bend away from the normal when passing through a material?
when the material has a lower density and the wave speeds up
what happens to the wavelength if a wave slows down?
it will decrease
what are sound waves?
longitudinal waves which cause particles to vibrate parallel to the direction of wave travel
how do we hear sound?
- ear canal
- eardrum
- three small bones transmit vibrations to the cochlea
what is the frequency of a sound wave related to?
pitch
what is the amplitude of a sound wave related to?
volume
what is the human hearing range?
20 - 20,000Hz
what are ultrasounds?
sound waves which have a frequency above 20,000Hz
what happens when ultrasound waves meet the boundary between two different materials?
- some are reflected
- the time taken for the waves to leave and return is measured
- the depth can be determined using the speed of sound and time taken
what are ultrasounds used for?
medical and industrial imaging
what are seismic waves?
vibrations produced by earthquakes in the earth’s crust
what are the types of seismic waves?
primary and secondary waves
what are the properties of p-waves?
- longitudinal
- faster
- can travel through solids and liquids
what are the properties of p-waves?
- longitudinal
- faster
- can travel through solids and liquids
what are the properties of s-waves?
- transverse
- slower
- can only travel through solids
what are seismic waves used for?
investigating the earth’s interior structure
what do s-waves suggest about the earth?
the outer core must be liquid as it cannot be detected on the opposite side of the earth
what do p-waves suggest about the earth?
there is a solid inner core as there are two shadow zones where none can be detected
what do all electromagnetic waves do?
- transfer energy as radiation from the source of the waves to an absorber
- travel through a vacuum
- travel at the same speed
When are A-scans used?
when the anatomy is known and the distance/depth measurements are needed
How does B-scans work in foetal scanning?
Gel is applied to the skin prior to the scan. The transducer array is moved over the skin of the patient about to view the body from a range of angles. Many pulses are sent into the body and partially reflected and partially transmitted at each boundary
Advantages of ultrasound to X-rays
- quite cheap, portable and do not need a specialist room
- good for imaging organs and soft tissues
(non-ionising. low intensities so no known hazards)
Disadvantages of ultrasound to X-rays
do not penetrate bone so cannot detect fractures or image the brain
resolution is poor so the scans cannot reveal fine detail
(Sonographer need to be skilled at operating the probe to get a good image)
Why does the amplitude of the traces decrease when there is an air gap in the metal block?
Some of the sound is reflected at the crack, so less sound is reflected at the far edge of the metal
Waves earthquakes generate are….
seismic waves
Why is it important to have seismometer stations at many locations all over the Earth?
We cannot predict when earthquakes occur and early detection allow warnings to be issued
How is the size of the core measured?
measuring shadow zones from sudden refraction as a wave travels from one layer to another
How is the density of the materials revealed?
The speed and trajectory of the waves
