11 + 12 + 13— Waves Flashcards
Frequency
No. Of oscillations each point completes per second
SI: Hz
Define Transverse waves
Transverse waves are waves that has a direction of vibration perpendicular to the direction of wire travel, transferring energy but not medium.
Eg EM waves
Period
Time taken by each point on the wave to complete 1 oscillation.
SI: s
In phase
Any points in a wave that move in the same direction and have the same speed and the same displacement from the rest position.
Wave speed/velocity
Distance travelled by each point on the wave per second
Amplitude
Maximum displacement of a point of a wave from its equilibrium position
SI: m
Wavefront
Imaginary line on a wave that joins all adjacent points in phase
Compressions
Regions of higher pressure than atmospheric pressure due to particles being close together
Rarefractions
Regions of lower pressure than atmospheric pressure due to particles being spread further apart
What happens when waves travel from deep to shallow regions
- Bend towards normal
- Speed decreases
- Wavelength decreases
- Frequency unchanged
Define sound waves
Sound is produced by vibrating sources placed in a medium which produce regions of compression and rarefraction, and are transmitted as longitudinal waves that have a direction of vibration and oscillation parallel to the direction of wave travel, in the presence of a medium.
Characteristics:
- Transmitted as longitudinal waves that consists of a series of compressions n rarefractions.
- Cannot propagate in a vacuum as it requires a material medium to travel.
Wavelength
Shortest distance betw any 2 points in a wave that are in phase, eg 2 successive troughs or crests or compression or rarefraction
Trough
Lowest point of a transverse wave
Crest
Highest point of a transverse wave
What does frequency affect
Pitch. ^f ^pitch
What does amplitude affect
^amplitude, louder the sound
Factors that affect echoes
- Distance (long)
- Area (large)
- Frequency (high)
Characteristics of speed of waves
- Travels fastest in solids, slowest in gases
- Depends on tempt. Tempt ^, faster
- Depends on humidity. Tempt ^, faster
Characteristics of electromagnetic waves.
- All em waves r transverse waves
- All em waves can travel without a medium, with the same spd of 3 x 10^8 m/s in a vacuum.
- Wave spd equation, v=f x (wavelength), applies to all em waves
- Em waves transfer energy
- Undergo reflections n rarefractions
Frequency of transverse waves from low to high.
Radio waves
Microwave
Infrared
Visible light
Ultraviolet
X-ray
Gamma rays
Colours:
Red
Orange
Yellow
Green
Blue
Purple
Uses of electromagnetic waves
R: radio & tv communication, RFID tags, RADAR (radio detection & imaging)
M: mobile phones, microwave oven, satellite TV
I: intruder alarms, infrared remote controllers, thermal imaging
V: optical fibres in medicine & telecommunicatios, photography
U: sun beds, disinfecting water, bank note authentication
X: security screening, medical radiology, industrial defect detection in metals
G: cancer treatment, sterilising food
Uses of echoes
Bats using echoes to move about
Sonar used by ships to determine depth of sea-bed
Sound and medium
- requires a material medium to travel, cannot travel in vacuum
- Bell jar experiment -> air pumped out, sound fainter n eventually cannot be heard
Audible frequencies
20Hz to 20 000Hz for human ear
What is meant by a frequency of 5.1kHz?
Air molecules vibrate to-and-fro, making 5100 complete vibration per second
Figure of sound wave with 2x frequency vs sound wave with x frequency.
Distance betw a compression and its neighbouring rarefractions decrease by 2 times.
Describe distance betw adjacent particles as wave travels thru the medium
Distance betw adjacent particles periodically increase to a fixed max distance n then decrease to a fixed min distance
Explain why 2 sounds r heard when experimenter bangs a pipe.
One sound is due to sound travelling thru metal pipe & the other thru air. Spd of sound thru pipe is greater than spd of sound thru air.
Different pipe w higher frequency: spd no change since spd of sound is not affected by frequency of sound.
Ultrasound
Sound of high frequency above the upper limit of the audible range of human, 20Hz to 20,000 Hz.
(Sounds of low frequency below human audible range is infrasound)
Reflection of sound
Sound is reflected if it is blocked by a hard surface.
Most of incident sound energy is absorbed, v little is reflected if surface is soft.
Explain how vibrations of tuning fork produce sound waves in air
Tuning fork vibrates and disturbs air molecules around it, causing them to vibrate to and fro about their equilibrium position. Disturbance of air molecules then passed on from molecule to molecule by collision, transmitting sound from tuning fork to microphone.
State and explain how the wavelength of the ultrasound wave in air compares with its wavelength in oil.
Wavelength decreases since ultrasound waves travel slower in gases than in liquids. Since frequency remains unchanged, by v = f x wavelength, wavelength decreases.
Briefly describe how ultrasound r used to obtain images of baby in womb.
Pulses of ultrasound r sent thru skin n soft body tissue of mother. When it encounters bone n cartilage tissue of the baby which is much denser, the difference in density causes ultrasound to undergo reflection. Source receives reflected ultrasound, time taken for reflected ultrasound to return is calculated n img is produced showing the depth of the baby.
Why X-rays r not used to obtain a pic of an unborn baby
X-rays r high frequency high energy electromagnetic waves that can cause dmg to cells n kill cells, harming the baby.
How sound energy is transferred without transferring matter
Air molecules collide w one another, transferring ke from one molecule to another
Why sound travels faster in solids than in gas
Sounds travel thru the passing of vibrations in a medium. When the molecules r closely packed tgt, transfer of vibrations betw molecules more efficient -> molecules in solids closely packed vs in gas far apart -> have a higher density -> sound travels faster in solids.
X-rays r a type of electromagnetic radiation used to produce images of the inside of the human body. State 3 possible effects on the living cells in the human body when X-rays r absorbed by body tissue.
- Death of cells
- Mutated cells
- X-rays interact w water molecules in human body to produce radicals and ions such asOH-, which can attack the cells and damage them or form toxic substances like H2O2.
If frequency of dipping motion increases, state 2 changes to circular water wavefronts observed. [2]
More circular wavefronts are seen
Distance between each wavefront decreases.
Volume of water in tray is reduced to half, frequency of dipper readjusted to original value. State 2 changes to the circular wavefronts observed. [2] (deeper to shallower water)
(Wavelength becomes shorter in shallower water)
More circular wavefronts are seen
Distance between each wavefront is narrower.
As water wavefront travel outwards, they become “fainter” and less observable. Explain why. [2]
Wave energy dissipates to thermal energy.
Amplitude of wave decreases until it becomes non-observable.
In terms of amplitude, wavelength and frequency, compared and comment on similarities and differences of the waves at the deep and shallow ends of the pool. [3]
F: same
A: shallow < deep (wave energy dissipates to internal energy as it reaches shallow)
W: shallow < deep (wave speed at shallow is slower than wave speed at deeper end)
Explain change in direction of wave motion when depth of pool changes [2]
When waves enter from deeper to shallow end, refraction of water waves occurs and wave speed decreases, thus waves bend towards normal at shallow ends. Hence, change in direction of waves occurs.
A leaf falls into the pond. Explain and state whether the leaf will move or otherwise. [2]
Leaf will stay at it’s original position or d metre away from edge of pond.
However, it will move up and down at its location following the perpendicular motion of transverse waves.
Other than spacing between particles, state 3 factors that affect speed of sound and 2 factors that do not. [2]
Dependent:
Wind, temperature and humidity of air
Independent:
Loudness and frequency of sound
State and explain whether speed of sound in warm air compares with speed of sound in cold air [2]
Sound travels slower in cold air than in warm air. [1]
The air particles in cold air travel slower and therefore take a longer time to collide with one another, resulting in sound travelling slower.
Describe differences betw the compression and rarefractions regions in terms of air density and pressure. [2]
Higher air density and air pressure in compression region than rarefractions region.
Source of a wave
A vibration or oscillation
Wave
A disturbance that propagates through space, transferring energy with it but not matter
Define longitudinal waves
longitudinal waves consists of a series of compressions n rarefractions and have a direction of vibration parallel to the direction of waves travelled.
Eg sound waves
Echo
Reflected sound from a surface heard after an interval of silence
Explain how sound energy is transferred through the wall without transferring matter. [2]
When a wave passes through the wall, the molecules will vibrate back and forth parallel to the motion of the wave and collide with one another, transferring energy by means of energy in kinetic store.
The energy of this wave is transferred through the wall from one side to the other via a series of compressions and rarefactions without transferring matter.
