P12 - Waves Flashcards
What is an ultrasound wave?
Sound wave at a frequency greater than 20,000 Hz (the upper frequency of the human ear)
What is amplitude
- Height of wave crest or trough from rest position (transverse wave)
- Closeness of coils in compression (longitudinal wave)
What is compression?
Squeezing together
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 frequency?
The number of waves passing a fixed point every second
What are longitudinal waves?
Waves in which the vibrations are parallel to the direction of energy transfer
What are mechanical waves?
vibrations that travel through a substance
Define Oscillate:
move to and fro about a certain position along a line
What is a Primary Seismic Wave (P-wave)?
Longitudinal waves that push or pull on the material that they move through as they travel through the earth
What is rarefaction?
Stretched apart
What is reflection?
The change of direction of a light ray or wave at a boundary when the ray or wave stays in the incident medium
What is refraction?
The change of direction of a light ray when it passes across a boundary between 2 transparent substances at a non-zero angle
What is a Secondary Seismic Wave (S-wave)?
Transverse waves that shake the earth side to side as they pass through
What are seismic waves?
Seismic waves are waves that travel through the earth, they are produced in an earthquake and spread out from the epicentre
What is wave speed?
The distance travelled by a wave every second
What is transmission/transmitted?
A wave passing through a substance
What is a transverse wave?
A wave were the vibration is perpendicular to the direction of energy transfer
What is a vibration?
Oscillate rapidly about a certain position
What is a wavelength?
The distance from one wave crest to the next
What is the period of a wave?
The time taken for 2 successive crests (1 wavelength) to pass a fixed point
What is a wave?
A series of oscillations that travel from one place to another, transferring energy
What is a wave crest?
The highest point above the reset point
What is a wave trough?
The lowest point below the reset point
What is the unit for frequency?
Hertz (Hz)
What is the equation for the period of a wave?
T (period) = 1 / f (frequency)
What is the equation for the speed of a wave?
V (speed of wave) = f (frequency) × λ wavelength)
What is the normal line?
The normal is a dotted line drawn perpendicular (90°) to the surface of the material, at the point of entry of the light.
What is the law of reflection
The reflected waves move away from the flat barrier at an angle equal to the incident waves (The angle of incidence = the angle of reflection)
What is the angle of incidence?
The angle between the normal and the incident ray
What is the angle of reflection?
The angle between the normal and the reflected ray
What is the incident wave?
The wave travelling towards a barrier or boundary
What is a reflected ray?
A ray of light that has been reflected off a surface
What is a refracted ray?
A ray that travels in another medium and undergoes a change of velocity
What is the equation for the distance of an object detected using sound?
Distance (m) = 1/2 x speed of wave (m/s) × time (s)
Explain how a light wave will be refracted depending on the material that it enters
- Light wave enters more dense medium:
- Slows down (more resistance)
- Bends towards the normal
- Light wave enters less dense medium:
- Speeds up (less resistance)
- Bends away from the normal
How would you demonstrate a mechanical longitudinal wave?
Pulling a slinky forwards and backwards
How would you demonstrate a mechanical transverse wave?
tying 1 end of a rope to a fixed position and moving the other end up and down
What medium do mechanical waves travel through fastest?
Solids
What medium do electromagnetic waves travel through fastest?
a vacuum
What type of wave is a sound wave?
mechanical and longitudinal
What is the pitch of a sound wave?
The frequency
What is the volume (loudness) of a sound wave?
The amplitude
What is an oscilloscope?
- Oscilloscope shows wave shapes of electrical signals
- Connected to a microphone, it shows wave shapes of sounds
Explain how we are able to hear noise of people talking loudly in another room
- Sound waves travel through air and walls to reach our ears.
- Walls speed up sound due to their solid structure.
- Air carries sound waves into our ears.
- Eardrums vibrate when hit by sound waves.
- Brain receives signals from small bones about the sound.
Explain how ships are able to detect the depth of water.
- Ships use echo sounding technique.
- Transmit high frequency sound wave.
- Wave reflects from ocean bottom, detected by ship.
- Calculate depth: Distance (m) = 1/2 × speed of wave (m/s) × time (s).
What is the speed of sound in water?
1500 m/s
What are 2 medical imaging techniques?
Ultrasound, X-ray
What is the range of human hearing?
20Hz - 20kHz
What is an infrasound wave?
Sound wave at a frequency lower than 20 Hz (the lower frequency of the human ear)
What is an ultrasound scanner?
- Ultrasound scanner: electronic device
- Uses a transducer
- Transducer placed on a surface
- Sends pulses of ultrasound waves
- Detects returning waves
- Results shown on a display screen
What are the uses of an ultrasound scanner?
Medical Imaging:
• Looking at organs inside the body
• Looking at damaged ligaments
• Looking at damaged muscles
• Looking at babies inside the womb
Ultrasound scanners can also be used for industrial purposes such as inspecting metals for defects and damage
Why can’t x-rays be used for a baby scan?
- X-rays show only the baby’s bones, not body and limbs.
- Cannot see development of important baby features.
- Ionising radiation from X-rays can be damaging to the baby.
What happens when an ultrasound wave hits organ tissue?
It is partially reflected
What happens when x-rays hit organ tissue?
They pass straight through
Explain exactly how an ultrasound scanner works
- Ultrasound pulse reflected at medium boundaries.
- Return time of reflected waves monitored.
- Detected waves used to create point-by-point image.
- Transducer moved for complete object image.
What is non-ionising radiation?
A type of low-energy radiation that does not have enough energy to remove an electron from an atom
What is the speed of sound in air?
330 m/s
What is the inner core?
The inner core is the central part of the earth, it is very dense, hot, and it mostly made from solid iron and nickel
What is the outer core?
The section of the earth after the inner core, made of iron and nickel, but liquid
What is the crust?
The outer layer of the earth that is very thin and made mostly of silicon, oxygen, and aluminium
What is the mantle?
A viscous semi-solid below the crust with convection currents circulating within it
What is the atmosphere?
A layer of gases that envelope the crust and the entire earth
What is the shadow zone?
the area of the Earth’s surface where waves are not detected following an earthquake
What is an earthquake?
- Earth’s internal forces from tectonic movement build up pressure.
- Pressure causes rocks to fracture.
- Fracture releases energy in seismic waves.
- Seismic waves are shock waves from sudden rock movement.
Describe the properties of P-Waves:
• The P stands for Primary.
• They are longitudinal waves (push-pull) and they are mechanical
• They can travel through liquid and solid so they can travel through the earths core
• They are the fastest seismic wave
• They are bent sharply by changing the density of the material that they’re travelling through
What determines whether a wave requires a medium to travel?
Whether it is mechanical or electromagnetic:
• Mechanical waves require a medium
• Electromagnetic waves do not require a medium
Describe the properties of S-Waves:
• The S stands for secondary
• They are transverse waves (up and down)
• They can only travel through solids
• They are slower than P-waves
• They are bent sharply by changing the density of the material that they are travelling through
Describe the properties of L-Waves:
- L-waves (Long Waves): Arrive last
- Cause violent surface movements: Up-down, backward-forward
- Travel slower than P and S waves
- Restricted to Earth’s crust
What type of seismic waves are detected first?
P-waves because they are the fastest form of seismic wave
What type of seismic waves can travel through the earths mantle?
P-waves, S-waves
What type of seismic waves can travel through the earths outer core?
P-waves
What happens to s and p-waves as they travel deeper into the earths mantle?
Their speed and direction change as the medium they travel through is more dense
What happens to P-waves as they travel across the boundary from the mantle to the outer core?
They refract away from the normal as the density of the medium they travel through is less dense
Use the detection of different seismic waves to provide evidence for the presence of a liquid outer core in the earths surface
- P-waves (longitudinal): Travel through solids and liquids.
- S-waves (transverse): Travel through solids, not liquids.
- Earthquake waves: P-waves and S-waves spread from the epicenter.
- Detection: P-waves detected globally; S-waves detected near the epicenter.
- Earth’s core: S-waves blocked by the liquid outer core, P-waves pass through.
- Conclusion: Liquid outer core exists, allowing P-waves but not S-waves.
- Shadow zone: Indicates P-waves are refracted by different density, confirming the liquid outer core.
What is an optically denser medium?
A medium in which light travels comparatively slower than the other medium
What is a rarer medium?
A medium in which light travels comparatively faster than the other medium
Describe how sound waves are produced by a drum and then heard
- Hitting the drum makes it vibrate.
- Vibrating drum skin vibrates nearby air particles.
- These vibrations form a longitudinal sound wave.
- Sound wave travels through air to the ear.
- It moves down the ear canal to the tympanic membrane, causing it to vibrate.
- Vibrations are converted to signals sent to the brain, creating the sensation of sound.
What is the tympanic membrane?
The ear drum
Explain how the human ear can only hear over a certain range of frequencies
- Human hearing limit: Eardrum maxes out around 20kHz
- Hearing range limited by eardrum capacity
- Ageing eardrum: Vibrates less, hearing range decreases
Explain the method for investigating waves in a liquid
- Gather apparatus: tray, water, ruler, stopwatch
- Measure and note tray length
- Fill tray with water to 5cm depth
- Elevate one end of tray 3cm, let other end touch ground
- Drop elevated end, time wave travel across tray
- Calculate wave speed: Tray length ÷ Time for wave
- Reduce water depth by 1cm, repeat steps 4-6
- Continue reducing water depth by 1cm, repeating steps 4-6 each time
- Time permitting, repeat entire process for mean average
- Record data in table or graph
What is are some examples of a mechanical wave?
Sound wave, Water waves, Seismic waves
What are some examples of electromagnetic waves?
Light waves, radio waves, and microwaves
What category of waves are electromagnetic waves?
All electromagnetic waves are transverse waves
What category of waves are mechanical waves?
Mechanical waves can be transverse or longitudinal
What type of waves can be transverse?
Both mechanical and electromagnetic waves can be transverse
What type of waves can be electromagnetic?
Only transverse waves can be electromagnetic
What is the direction of oscillations in a transverse wave?
In a transverse wave, the direction of oscillation is perpendicular to the direction of energy transfer
What is the direction of oscillations in a longitudinal wave?
The oscillations of a longitudinal wave are parallel to the direction energy transfer
What happens if a wave has a larger amplitude?
It carries more energy
What happens if a wave has a larger amplitude?
It carries more energy
Why can you see lighting before you hear the thunder?
Because the speed of light is greater than the speed of sound
What happens if a wave hits a barrier?
- Reflection occurs at the barrier.
- Reflected wave front moves away at the same angle as incident wave front.
- No change in speed or wavelength.
What happens when a wave meets a boundary with a different substance?
It may be:
• Totally or partially reflected
• Transmitted through the substance
• Absorbed by the substance
What happens when a wave passes through a substance?
As waves travel through a substance, the amplitude of the waves decreases as the substance absorbs some of the waves’ energy
What is used to detect seismic waves?
A seismometer
What frequency of sound is most detectable to humans?
3kHz
What can waves not transfer?
Matter
What method is used to detect objects underwater?
echosounding
Which seismic waves are transverse waves?
S-waves
What changes during refraction?
change in speed, direction and wavelength of the waves
