P5.1 Flashcards
What is amplitude?
Symbol and unit
Distance from the middle to the top (crest) or bottom (trough) of a wave β> the bigger the amplitude, the more energy that the wave carries
A
depends on wave (m/volts)
What is wavelength
Symbol and unit
Distance from one point on a wave to the same point on the next wave β> the bigger the wavelength, the smaller the frequency
Ξ» (Lambda)
Metres(m)
What is frequency?
Symbol and unit
Itβs the number of waves/ oscillations per second
F
Hertz,Hz
What is the time period
The time for one wave to pass a given point of time taken to produce one wave
T
Seconds (s) - 1 /Hz (frequency)
What is a wave
Itβs an oscillation/ physical phenomenon that transfers energy
Itβs a disturbance in a medium that transfers energy without transferring matter - always in motion so the wave diagrams should be imagined moving from left to right
What type of waves are used to communicate between two phones
Electromagnetic waves
Donβt need a medium to travel through
What type of waves are sound and water
They are mechanical waves and they need a medium (matter) to travel through
What are longitudinal waves
- The oscillations are parallel to the energy transfer (direction of vibration of individual air molecules is the same way as the direction of the wave)
- it consists of rarefactions and compressions
- e.g. = sound waves or P waves = can travel through liquids
What are compressions and rarefactions?
Compressions are particles squashed together = high pressure and PEAKS
Rarefactions are particles spread apart = low pressure and TROUGHS
- the Hz of longitudinal waves is the no. of compressions passing a point per second
What are transverse waves
- the oscillations are perpendicular to the energy transfer (the direction of vibrations is at right angles to the direction of travel of the wave)
- has a peak/ crust (top of the wave) and has a trough (bottom of the wave)
- e.g. light/ EM waves/ S waves
What is the normal line
Itβs the position of a particle about which the wave vibrates / oscillates
What does the time trace of a wave show
It shows how the displacement varies with time at a particular position
What does the snapshot of a wave show
It shows how the displacement varies with distance at a particular time
How can you give evidence that the wave travels and not the water or the air?
You can use ripples on water to model transverse waves and you can show how waves are reflected
- surface of the wave moves up and down as the wave moves through the water
- by putting a small cork on the surface you can see that the wave travels but not the water
Same thing happens for sound waves but the wave moves from your mouth but the air doesnβt
How can you calculate wave velocity?
wave velocity (m/s) = frequency (Hz) x wavelength (m)
unit of frequency is the number of waves per second so:
Hz = 1/s
1 KHz in Hz
1000 Hz
What type of waves are ripples on a tank used to model
Transverse waves
What types of waves are sound waves in the air
Longitudinal waves
How can generate a sound with a specific frequency and find the wavelength of the sound waves generated?
- attach signal generator to a speaker
- use 2 microphones and an oscilloscope to find the wavelength of the sound waves generated
How do you use an oscilloscope to measure the speed of sound?
- Set up oscilloscopes so that detached waves at each microphone are show as separate waves
- start= both microphone next to speaker = then slowly move one away until the two waves that aligned on the display but have moved exactly 1 wavelength apart
- measure distance between microphones to find one wavelength
- use v= fΞ» to find speed (v) of sound waves passing air
- the frequency is what you set the signal generator to in the first place
How can you generate waves in a ripple tank?
- use a signal generator attached to a dipper
- signal generator moves dipper up and down = creates water waves at fixed frequencies
What does the trace of a transverse wave on the screen of an oscilloscope show
It shows the variation of pressure of time (not the sound wave itself)
How do you measure the frequency in a ripple tank?
- need cork and stopwatch
- float cork in wave = bobs up and down as wave passes it
- when cork is top of wave(Bob) start stopwatch
- count how many bobs in certain time (30 secs)
- divide the number by your time interval (bobs /30) = bobs per second = frequency in Hz
Keep amplitude of wave, position of dipper and depth of water same = fair test and do three repeats on average
How do you measure the wavelength in a ripple tank?
- use strobe light
- place card covered with cm squared paper behind ripple tank
- turn on stove light and adjust frequency until waves appear to freeze
- using the squared paper measure distance that five waves cover and divide distance by no of waves = average Ξ»
Keep amplitude of wave, position of dipper and depth of water same = fair test and do three repeats on average
How do you measure the velocity or wave speed in a ripple tank?
- need pencil and stopwatch
- place paper next to tank
- as waves move across tank = track path of one of the crests in the water on paper with pencil (use ruler)
- another person should time how long the first has been drawing for (pick time to stop e.g. 10 secs)
- length of line = speed x time
Keep amplitude of wave, position of dipper and depth of water same = fair test and do three repeats on average
How do you measure the velocity of ripples with without doing the practical?
- find wavelength (by using a flashing light (a strobe) and a ruler)
- fine frequency (number of rotations of the motor per second)
- use the calculator to work out the wave velocity
How can the velocity of sound vary and why?
- it can vary with the temperature and the pressure
- because these factors effect the velocity at which the disturbance in the wave is transferred between the particles
How can you measure the velocity of sound?
- time how long it takes to hear an echo of a clap when you are at distance from a sound and then do velocity = distance / time
- also you can connect a pair of microphones a certain distance apart to an oscilloscope
How can you make transverse and longitudinal waves on a slinky?
Transverse = lay the slinky left to right and then oscillate its up and down Longitudinal = lay the slinky leg to right and then oscillate it left and right
Will moving your hand faster when you make a transverse wave on a slinky spring increase the velocity of the wave on the slinky?
- moving your hand faster will produce move waves and therefore increase the frequency of the waves produced.
- velocity will remain unchanged as the velocity of a wave depends only on the medium (water/air/steel) that the wave travels through - not how quickly the peaks are produced.
What three things happen to waves at a boundary?
- absorb = transfer energy to the materialβs energy stores
- transmitted = carries on travelling through new material at diff speed (refracts)
- reflect =incoming ray is sent back, away from the second material
What is the angle of incidence equal to and when?
- in reflection angle of incidence =angle of reflection
- measured from the normal
What happens in reflection?
- light bounces off objects into our eyes
- light rays reflect off smooth surfaces all in the same direction = giving a clear reflection (light on mirror)
- light rays reflect off rough surface = all directions so ray hits at diff angle
- angle of incidence = angle of reflection
What is white light a mixture of?
- diff colours of light which have diff wavelength
- all colours of light on white are reflected at same angle and it doesnβt split into diff colours when it reflects as all wavelength follow incidence = reflection
What happens when waves travel in different speeds with different densities?
- refraction as = when wave crosses a boundary it changes speed
- frequency stays the same
- wavelength decreases as the wave slows down and increases if it speeds up
What happens when a wave hits the boundary at an angle to the normal?
- change speed and wavelength makes wave bend
- more change in speed = more it bends
What happens when waves slow down and speed up?
- slow = bend towards the normal
- fast = bends away from normal
Where do sound waves travel faster?
-faster in denser material so wavelength increases from water to air
How can you find out how far away a boundary is?
- need to know the speed of the wave in the medium
- you can use the time it takes for the reflections to reach the detector
- use formula speed x time = distance to find out how faraway the boundary is
Where do EM waves travel slower?
EM waves like light travel slower in denser so air to glass the wavelength decreases and bends toward the normal
What is effect how much an EM wave refracts?
- effected by wavelength = shorter wavelengths bend more
- shortest wavelength = violet and longest = red
- air = same speed but denser = shorter = bends more towards normal
Why canβt we hear ultrasound?
- as frequency is greater than 20 000Hz
- we canβt hear it but dogs can
Why is ultrasound useful?
- ultrasound = small wavelength so can focus it into a beam
What happens when ultrasound waves hit your body?
- ultrasound waves can pass through body
- but partially reflected at boundaries between the tissues
- e.g between the muscles in a pregnant womanβs and the fluid in her womb
- or between the fluid in the womb to the skin of the foetus
How can we use ultrasound to prove a 3D image of a foetus?
- transmitter beams ultrasound waves to mother
- wave reflects from diff boundaries
- if you know the speed of ultrasound in different tissues you can calculate the distance to diff boundaries
- reflections are processed by computer = makes an image
How else can we use ultrasound except for a developing foetus and is it harmful?
- examine soft tissues/organs - kidney,liver and bladder
- monitor blood flow
- kidney stones
- completely safe
In what materials can ultrasound be used to find flaws and how?
- objects like pipes or material like wood/metal
- ultrasound waves entering a material will usually be reflected by the far side of the material
- if there is a flaw like a crack inside object then wave reflects sooner
What is refraction?
When a waveβs velocity and direction change when it travels from one medium to another
What happens when a sound wave hits a solid?
- echoes, reflecting many times and eventually absorbed
- absorbed = particles in wall vibrate = get hotter
How does a microphone produce sound?
- diaphragm of the microphone absorbs the sound waves
- produces a changing electrical signal
In what states do sound waves move faster?
Faster in solids than liquids
Faster in liquids than gases
- frequency doesnβt change from one medium to another, but the wavelength changes (longer = speeds up and shorter = slows down)
Why are sound waves hard to spot in normal circumstances and where will they be reflected?
- they refract as they enter diff media but since they are always spreading our = the change in direction is hard to spot.
- they reflect by hard flat surfaces (echoes = reflected sound waves)
Why canβt sound travel in space or a vacuum?
- space is mostly a vacuum
- there are no particles to move or vibrate
What is the ear designed to do?
- detect, amplify and convert sound into electrical signal
How do ears detect sound?
- outer ear (pina and auditory canal) gather sound waves and directs it to ear drum = vibrates
- vibrations passed on to ossicles = amplify the sound and pass it on to inner ear through oval window
- cochlea is filled with fluid which transmits vibrations from the oval window to the small hairs on cochlea wall
- hairs attached to detecting cells = release chem substance to trigger nerve impulse down auditory nerve to brain = processes signal = sound
How does your brain interpret sound?
- interrupts signals as sounds of diff pitches and volumes depending on frequency and intensity
- high frequency = high pitch
What is the natural frequency
Frequency at which an object oscillates if itβs displaces
What is resonance?
Itβs a large amplitude oscillation which happens when you make something oscillate at its natural frequency
How is human hearing limited?
- limited by the size and shape of our eardrum and the structure of all the parts within ear that vibrate to transmit sound
Why can younger people hear higher frequencies?
- hairs in cochlea have diff lengths and resonate at diff frequencies
- range of hair length = range of sounds you hear
- as you get older the shorter hairs are lost so you struggle to hear higher frequencies
What frequencies can younger people hear?
- younger people can hear 20Hz - 20 000Hz and as you get older the upper limit decreases = need louder sounds for you to hear (due to wear and tear of cochlea/auditory nerve)
What is meant by the normal of a boundary?
- a line at right angles to the boundary
What happens when light meets the boundary from air to glass?
- light travels through glass easily and only transmits if meets at an angle
- when light is reflected = starts at the exact point where itβs reflected and angle of reflection= angle of incidence
How do you know a material is less more dense from before?
- a velocity of the light is faster and closer to the normal
What happens to a wave when it enters a vacuum?
- the frequency stays the same
- the wavelength increases as the vacuum the less dense than glass and the velocity speeds up
One side of the prism has a red tinge whilst the other is purple. Explain why?
- white light has diff wavelengths of diff colours
- that means that if travelling at the same speed = all are white but when refracted the wavelengths are refracted at diff. lengths
- shorter wavelength (blue) so refracted more so closer to normal than longer wavelength (red)
