Topic 12 - Wave Properties Flashcards
What is wave amplitude?
The height of a wave crest or trough of a transverse wave from rest position. For oscillating motion, the amplitude is the maximum distance moved by an oscillating object from its equlibrium.
What is a compression?
The frequency of waves highly increasing in a certain area.
What is an echo?
A reflection of sound that can be heard.
What are electromagnetic waves?
Electric and magnetic disturbances that transfer energy from one place to another.
What is wave frequency?
The number of wave crest passing a fixed point every second.
What is a longitudinal wave?
A wave in which the vibrations are parallel to the direction of energy transfer.
What are some examples of longitudinal waves?
Sound waves and Seismic P waves
What is a transverse wave?
A wave in which the vibrations are perpendicular to the direction of energy transfer.
What are some examples of transverse waves?
Water, light, gamma and microwaves.
What does it mean if a wave oscillates?
The wave moves to and fro about a certain position along a line.
What is a mechanical wave?
A vibration that travels through a substance.
What is a primary seismic wave? (P wave)
A longitudinal wave that pushes or pulls on the material it travels through.
What is a secondary seismic wave? (S wave)
A transverse wave that shakes the ground from side to side as they pass through it.
What is rarefaction?
When wave frequency highly decreases in an area.
What is reflection?
A change in direction of a light ray or wave when it passes across a boundary between two transparent substances (this includes air).
What is refraction?
A change in direction of a light ray or wave at a boundary when the ray or wave stays in the incident medium. The wave speed changes (which also changes the wavelength).
What is a seismic wave?
A sound wave travelling through the ground that is caused by tectonic activity with a frequency greater than 20,000 hertz (the limit of frequency the human ear can detect).
What is wave transmission?
A wave passing through a substance.
What is an ultrasound wave?
A sound wave at frequency greater than 20,000 hertz used to generate images of the body.
What does it mean when a wave vibrates?
It oscillates (moves to and fro) about a certain position.
What is wavelength?
The distance from one wave crest to another.
What is a wave medium?
The substance through which a wave travels.
What is time period? (in relation to waves)
The time taken for a wave to pass a point.
What are hertz?
The unit of frequency in electrical mainz. Measures the number of waves passing a point per second.
What is the relationship between frequency and time period?
Frequency = 1/ time period.
What is the equation for wave speed?
Wave speed (m/s) = frequency (Hz) x wavelength (m)
What are wavefronts?
The peak of a transverse wave or the compression of a longitudinal wave?
What are the features of reflection?
The waves are reflected at the same angle they strike at.
- No change in frequency.
- No change in wavelength.
- No change in speed.
- Direction of travel changes.
- All waves reflect.
What are the features of refraction?
- No change in wave frequency.
- Decrease in speed makes the wavefronts close upon each other.
- Direction of wave travel changes unless it travels at 90 degrees to the new medium.
What is a signal generator?
An electronic device that generates an electrical signal that can be used by a vibration generator.
What is a vibration generator?
A device that uses electrical impulses generated in a signal generator to make mechanical waves for example on a string.
What is pitch of a sound wave?
The quality of the sound governed by the frequency of vibrations.
What is loudness of a wave?
The amplitude of a sound wave.
What is a seismometer?
A device measuring the amplitude of seismic waves.
What is SONAR?
Sound Navigatiom and Ranging
Why can’t sound travel through a vacuum like outer space?
Since sound vibrates particles and sicnce there are very few particles there is very little sound.
What materials can P waves travel through?
Solids, liquids and gases since they are longitudinal.
What materials can S waves travel through?
Only solids as they are transverse.
How can thermal energy under the earth’s surface cause earthquakes? [P12 Review Question]
-Magma is in the mantle moves around in convection currents.
-The mantle is made of plates (which move)
-There is a build-up of pressure/force/energy when plates slide under/over/past each other.
-A sudden movement when pressure becomes too great.
-This sudden movement of plates is an earthquake.
What is the definition S wave motion? [P12 Review Question]
-The ground moves up and down when impacted.
-The waves oscillate perpendicular to the direction of travel.
How were P and S waves used to study the make up of the earth? [P12 Review Question]
-The use of seismometers
-Waves can be refracted in the interior of the earth
-Some seismic waves are longitudinal and some are transverse
-S/transverse waves cannot pass through liquids.
-S wave/transverse waves’ shadow zones show that part of the Earth’s composition is liquid (outer core)
-P/Longitudinal waves can go through the core/liquid.
What are mechanical waves?
Waves that travel through a medium as vibrations.
What examples of mechanical waves are there?
Sound waves, water waves, spring waves, rope waves, seismic waves produced by earthquakes.
What type of wave are light waves, radio waves and microwaves?
Electromagnetic waves.
How fast do electromagnetic waves travel?
At the speed of light with no medium.
What is true about oscillation in transverse waves?
Oscillations are perpendicular to the direction of waves transferring energy.
What is true about oscillations of a longitudinal wave?
Oscillations are parallel to the direction in which waves transfer energy.
What happens as amplitude of waves increase?
They carry more energy
What is wave period equal to?
1 / frequency
What happens when plane waves cross a boundary at a non-zero angle?
Each wavefront experiences a change in speed and direction
What happens to waves that aren’t absorbed by a substance as they travel through it?
They are transmitted through it
How do loudspeakers work?
A signal generator generates waves
The loudspeaker emits the waves
The air vibrates as waves are transmitted through it.
What is an echo?
A sound that you hear as a result of sound being emitted back towards you.
What is the difference between musical notes and general noise?
Music has a rhythm, the sound waves change smoothly and the wave pattern repeats regularly,
General noise is made up of sound waves that vary in frequency.
What is the range of human hearing?
20-20,000 hertz frequency
What is echo sounding?
A technique using pulses of high-frequency sound waves to detect objects deep underwater and measure water depth below a ship.
The total distance travelled is both ways, therefore, distance is 0.5 x velocity x time taken.
What are ultrasound scanners used for?
Getting images of damaged organs or viewing prenatal scans of a baby in the womb.
What happens to ultrasound waves pulsed from the transducer?
They are partially reflected from the different tissue boundaries in its path.
They return to the transducer as a sequence of waves reflected by the tissue boundaries, arriving at different times.
What are ultrasound waves used for in medicine?
Ultrasound waves are used by eye surgeons when they need to know how long an eyeball is.
What are earthquakes generated by?
Shifts in tectonic plates in the mantle.
What is the focus of an earthquake?
The point from which an earthquake originates under the surface.
What is the epicentre of an earthquake?
The point at the surface nearest to the focus.
What are seismic P-waves?
They are the waves which cause the initial tremours lasting about a minute.
They are longitudinal.
They push or pull material as they move through the Earth,
What are seismic S-waves?
Waves that cause subsequent tremours a few minutes later than P-waves. They shake material up and down inside the Earth.
What are seismic L-waves?
Waves that arrive last and cause violent movements on the surface up and down as well as backwards and forwards. They are slower than P or S waves.
What happens to P and S waves as they travel through the mantle?
They bend as their speed gradually changes with depth and thus direction changes.
Which waves can and cannot travel through the liquid core?
P-waves are longitudinal and refract at the boundary between the mantle and the outer core.
S-waves are transverse and so they cannot travel through the liquid core.
How does the existence of the shadow zone show there is a liquid core?
P-waves are refracted at the boundary, because the second refraction is further around, they can’t reach the shadow zone.
S-waves can’t travel through the outer core because they are transverse waves and can’t travel through liquids.
Weak P-waves detected in the shadow zone show that the core has a solid inner part that refracts P-waves at the boundary between the outer core and the inner core into the shadow zone.
The boundary between the crust and the mantle of the Earth was discovered when it was found that the speed of the seismic waves changed at a depth of about 50km below the surface.
