P12 - Wave Properties Flashcards
What is the nature of waves / what are they?
Waves transfer energy without transferring matter.
*can also transfer information (e.g radio, mobile phone…)
What do all waves involve?
Oscillations/vibrations of some sort.
What pieces of equipment can be used to investigate the properties of waves?
E.g wavespeed, distances etc…
1) Ripple Tank
2) String
3) A solid object
4) A loudspeaker
5) Slinky
Etc…
What 2 categories do waves fall into?
1) Mechanical Waves
2) Electromagnetic Waves
What are Mechanical Waves?
Mechanical waves are oscillations (vibrations) that travel through a medium.
E.g sound waves, water waves, seismic waves from earthquakes etc…
What are Electromagnetic Waves?
Electromagnetic waves are waves that can travel through a vacuum at the speed of light (300,000,000m/s)
No medium is needed.
E.g light waves, radiowaves, microwaves etc…
How do mechanical waves travel?
Either:
Transverse
Longitudinal
How do electromagnetic waves travel?
ONLY Transverse
What is the top of the wave called?
The peak or crest.
What is the bottom of the wave called?
Trough
What is amplitude?
The maximum displacement of a point on the wave from the mean position.
Visually: the distance between the equillibrium line to the top OR bottom of a wave.
How does amplitude impact the amount of energy a wave can carry?
The bigger the amplitude, the more energy the wave carries.
What is wavelength?
Wavelength is the length of one complete wave.
Visually: the distance between one point on the wave, to the equivalent point of the adjacent wave.
Symbol of Wavelength: λ (lambda)
What is Frequency?
The number of waves passing a fixed point per second (or number of oscillations per second).
Unit: Hertz (Hz) e.g 10Hz = 10 oscillations per second.
What is the relationship between frequency and wavelength?
The higher the frequency, the shorter the wavelength.
What is the period of a wave?
The period of a wave is the time taken for each wave to pass a fixed point.
How do you calculate the period of a wave?
period, T (seconds) = 1 / frequency, f (Hz)
IMPORTANT: This is for 1 wave. If it’s any other number, you use that number.
E.g average period of ten waves = 10 / frequency
What wave property affects the pitch of a sound wave, and the colour of a light wave?
Frequency
*Think Football Pitch - ‘F’ for frequency, ‘P’ for pitch.
What wave property affects the volume of a sound wave, and the brightness of a light wave?
Amplitude
*Whence the phrase, turn the volume up. Means increase the amplitude.
What is wavespeed?
Wavespeed is the distance travelled by a wave in a given time.
What is the equation for wavespeed?
Wavespeed = frequency x wavelength
V = f x λ
(m/s) = (Hz) x (m)
*You can also just use speed = distance/time - make sure to always give equipment for the variables (e.g stopwatch for time, metre rule for distance).
How do waves travel?
1) Transverse
2) Longitudinal
What are Transverse Waves?
Waves where the oscillations of particles are perpendicular to the direction of energy transfer.
- vibrations are going up and down
- but the energy is being transferred from left or right
- vibrations are PERPENDICULAR to the direction of energy transfer
Visually: It’s like the worm dance move.
Example:
-All electromagnetic waves travel as transverse waves. E.g light, seismic s-waves…
What are Longitudinal Waves?
Waves where the oscillations of the particles are parallel to the direction of energy transfer.
- the oscillations are going from left to right
- the energy transfer is also going from left to right
- vibrations are PARALLEL to the direction of energy transfer
- there are ‘compressions’ and ‘rarefactions’
Visually: It’s like a slinky.
Example:
- Soundwaves are longitudinal waves.
- Seismic p-waves are longitudinal waves.
What is reflection?
The bouncing of light off a polished surface (mirror), that laterally inverts an object.
How does the angle of incidence and the angle of reflection compare in reflection?
EQUAL
i° = r°
How can plane waves in a ripple tank show how waves reflect?
- Plane (i.e straight) waves in a ripple tank are reflected from a straight barrier at the same angle to the barrier as the incident waves - (Law of reflection).
- This is because their speed does not change.
How do plane waves behave if they enter a new material?
Plane waves crossing a boundary between 2 different materials are refracted as the waves change speed.
They are not refracted if the waves cross the boundary at normal incidence.
What is refraction?
The bending of light caused by waves changing speed.
Why does refraction happen?
Refraction happens because waves change speed as they enter a new material’s boundary.
What is the refractive index, n of a material?
How optically dense a material is.
symbol for refractive index = n
What is the refractive index of air?
n = 1
This is fairly low, so waves in air travel quite fast.
What happens to a refracted ray when it slows down at a boundary (fast to slow)?
The rule is that if light goes from fast to slow, the refracted way goes towards the normal.
remember with ‘fast’:
‘f—>st’ - fast to slow = towards normal
Example:
- A wave is travelling in air (n=1) and goes through a perspex block (n = 1.5 - optically denser).
- The wave slows down as it enters the block - this particular change of speed bends the light towards the normal.
What happens to a refracted ray when it speeds up (slow to fast)?
The rule is that if light goes from slow to fast, the refracted way will go away from the normal.
remember with ‘sofa’:
’s—>fa’ slow — fast = away way from normal
Example:
- A wave is travelling through a perspex block (n=1.5) and passes through the object into air (n=1).
- The wave speeds up as it leaves the block - this particular change of speed bends the light away from the normal.
What is the difference between transmission and absorption?
Transmission = let through Absorb = to take in
Examples:
- food absorbs microwaves which heats up the food.
- ordinary glass lets light through, but darkened glass absorbs light.
What are Sound Waves?
Longitudinal vibrations that travel through a medium.
Can sound waves travel through a vacuum (e.g outer space)?
No - they are not electromagnetic waves
Why are musical notes easy to listen to?
The sound waves change smoothly and the wave patterns repeat regularly - rythmic.
What is general noise that you might hear in the street made up of?
Sound waves that vary in frequency with no repeating pattern.
What frequency range can the human ear detect? How do we hear? How do echoes work?
20Hz to about 20kHz (20,000 Hz)
Sound waves makes your ear drum vibrate - this sends a signal to the brain.
Echoes are sound waves reflecting back.
How does the pitch of a note increase?
Increasing the frequency
How does the volume of a note increase?
Increasing the amplitude
What are ultrasound waves? What are infrasound waves?
Ultrasound waves - sound waves above the highest detectable frequency of 20,000Hz.
Infrasound - sound waves below the lowest detectable frequency of 20Hz
What are ultrasound waves used for?
- Prenatal scans of babies in the womb.
- Used to capture images of organs in the body (e.g a damaged kidney, ligament or muscle).
- Bats use ultrasound waves to gather information as they are blind.
What is an ultrasound scanner made up of? How does it work?
An ultrasound scanner is made up of an electronic device called a transducer (placed on the body), a control system and a display screen.
How it works:
- The transducer produces pulses of ultrasound waves.
- The waves are partially reflected from the different tissue boundaries in their path.
- The waves then return to the transducer as a sequence of reflected ultrasound waves.
- An image is then built up on the screen.
What are the advantages of using ultrasound waves for medical scanning?
- Can be used to scan organs and other soft tissues in the body.
- Non-ionising radiation. The radiation does not have enough energy to remove an electron to ionise and atom or molecule. Therefore it is safe and harmless.
What is the study of earthquakes called?
Seismology
What causes earthquakes? What is the energy from earthquakes transferred as?
Forces inside the earth suddenly increasing and becoming strong enough to break, and move layers of rock.
This transfers a lot of energy - transferred as sesimic waves (shock waves).
What are the shockwaves that travel through the earth as a result of an earthquake called?
Seismic waves
Why is studying seismic waves important?
Seismology and the study of seismic waves provides information about the structure of the earth.
What are the 4 main layers of the earth?
1) Crust - 50km thick - solid
2) Mantle - molten rock
3) Outer Core - liquid
4) Inner Core - solid
Which layer of the earth do earthquakes happen in?
The Crust - earthquakes originate hear and move down into the lower layers of the earth.
What is the point where an earthquake originates called?
The focus
The nearest point on the earth’s surface (above ground) to the focus is called what?
The epicentre - the nearest point on the earth’s surface to the focus of an earthquake.
What equipment detects where the epicentre of an earthquake is?
A Seismometer
What are p-waves?
P-waves (primary waves) are the fastest kind of seismic wave. They arrive first and cause the initial tremors lasting about one minute.
P-waves are longitudial waves.
What are s-waves?
S-waves (secondary waves) arrive second and travel more slowly - takes longer to shake the rocks.
They cause more tremors a few minutes after the p-waves and shake the material that they pass through from side to side.
S-waves are transverse waves - but not light - so s-waves are slower than p-waves as they have to shake the rocks - cannot travel through a liquid.
What are L-waves?
L-waves (long waves) arrive last and cause violent movements. They travel very slowly but cause a lot of damage both on the earth’s surface and below.
How do p-waves, s-waves and L-waves refract in the earth? Why?
Their refraction happens as their speed changes as a result of changes in density.
- P-waves and S-waves both bend as they travel through the mantle.
- P-waves refract at the boundary between the mantle and the liquid outer core.
- *S-waves do not refract at the boundary between the mantle and the liquid outer core (transverse).
Why:
-*Transverse waves move perpendicularly to the direction of energy transfer, so in a gas or liquid (medium), there is no mechanism for a driving motion.
How does the the refraction of p-waves and s-waves in the mantle help scientists to locate the focus and epicentre of earthquakes?
It enables scientists to track back and find where the epicentre of an earthquake is/was/will be.
What are shadow zones? What angular distances to they fall between? What do shadow zones prove about the structure of the earth?
Shadow zones are areas of the earth’s surface, between 105° to 142° (angluar distance from the earthquake), where seisometers cannot detect any p-waves or s-waves - only L-waves.
This occurs as s-waves cannot enter the liquid outer core, and p-waves bend away from this particular area of the earth’s surface.
This is why shadow zones prove that there is a liquid outer core under the mantle.
What evidence is there for a soild inner core?
-Weak p-waves detected in the shadow zones show that the outer core has refracted them and must therefore be soild.
How was the boundary between the crust and the mantle discovered?
Scientists realised that the speed of seismic waves changed at depths of around *50km.
*Crust = 50km thick
