SP4: waves Flashcards
what are waves?
oscillations about a rest point
longitudinal waves
a wave that moves in the same direction as the direction in which the particles are vibrating
PALS
pa = parallel, p waves
l = longitudinal
s = sounds (ultrasound)
transverse waves
a wave that moves in a direction at right angles to the way in which the particles are vibrating
PET
pe = perpendicular
t = transverse
e = EM waves (light, S waves)
what are mechanical waves?
-need a medium to travel through
-cause oscillations of particles
mechanical waves examples
longitudinal or transverse
what fields can EM waves cause oscillations in?
electrical and magnetic fields
what do waves transfer?
energy and information, not matter
rest position
the position where the wave is at rest
displacement
the distance that a certain point in the medium has moved from its rest position
peak/crest
the highest point of a wave
trough
lowest point of a wave
amplitude
the maximum displacement of a point of a wave from its rest position
wavelength
the distance between two corresponding parts of a wave, usually measured peak to peak or trough to trough
time period
the time taken for a full cycle of the wave, usually measured from peak to peak, or trough to trough
frequency
the number of waves that pass a given point per second
what areas do longitudinal waves show?
-areas of compression (high pressure due to particles being close together)
-areas of rarefaction (areas of low pressure due to particles being further apart)
the movement of longitudinal waves
(using a spring)
-the compressions move from left to right
-energy is transferred from left to right
-none of the particles are transported along a longitudinal wave, they move backwards and forwards between compressions as the wave is transmitted through the medium
the movement of transverse waves
(using a rope
-the ropes move up and down, producing peaks and troughs
-energy is transferred from left to right, however, none of the particles are transported along a transverse wave
-the particles move up and down as the wave is transmitted through the medium
time period formula
1/frequency
how to calculate wave speed:
frequency (hz) × wavelength (m)
how are sound waves passed on?
collisions between particles
speed of sound in steel:
6,000 m/S
speed of sound in water:
1500 m/s
speed of sound in air:
330 m/s
does light or sound travel faster in air?
light
aim of measuring waves in a ripple tank practical
to measure the frequency, wavelength and speed of waves in a ripple tank
core practical: measuring wave speed from a ripple tank (steps)
- set up the ripple tank with about 5 cm depth of water
- adjust the height of the wooden rod so that it just touches the surface of the water
- switch on the lamp and motor and adjust until low frequency waves can be clearly observed
- measure the length of a number of waves then divide by the number of waves to record wavelength (it may be more practical to take a photograph of the card with the ruler and take your measurements from the still picture
- count the number of waves passing a point in ten seconds then divide by ten to record frequency
- calculate the speed of the waves using: wave speed = frequency × wavelength
can sound travel through a vacuum?
no, sound must travel through matter and there is no matter in vacuums
refraction
the change in direction of a wave at such a boundary
which wave types can be refracted?
all
why does refraction happen?
because waves’ speed changes when the waves enters a more or less dense medium
FAST
faster = away from normal
slower = towards the normal
4 things that can happen to waves at a boundary
TARR
-transmitted, absorbed, refracted, reflected
transmission
the passage of light through a material
absorption
energy is ‘taken-in’ by the material and the internal energy of the material will increase
reflection
the bouncing back of a wave when it hits a surface it can’t pass through
law of reflection
angle of incidence = angle of reflection
what does wavelength have a big effect on?
how much of a wave’s energy is reflected, absorbed or transmitted at an interface
if a wave slows down, its wavelength will…
decrease
the amount that the wavelength is changed affects the amount that the ________ changes
direction
how UV is used in greenhouses:
-UV light has a short wavelength, this is mostly transmitted by the glass
-the plants, soil and floor in the
greenhouse mostly absorb ultraviolet, and their temperature rises
how IR is used in greenhouses:
-the plants, soil and floor emit infrared light which has a longer wavelength that is mostly reflected by glass
-the infrared can’t escape the greenhouse and reflects until it is re-absorbed by objects inside the greenhouse
-the amount of energy in the greenhouse rises so its temperature increases
how is the frequency of a sound wave is related to the pitch that is heard?
high frequency waves = high pitch
low frequency waves = low pitch
how is the amplitude of a sound wave is related to the volume of the sound?
high amplitude = loud
low amplitude = quiet
human range of hearing
20-20,000 hz
how does the human ear detect sound?
-sound waves enter the ear canal and cause the eardrum to vibrate
-three small bones transmit these vibrations to the cochlea
-this produces electrical signals which pass through the auditory nerve to the brain, where they are interpreted as sound
infrasound
sound waves with frequencies below 20 Hz
ultrasound
sound waves with frequencies above
20,000 Hz
uses of ultrasound
-foetal scanning
-navigation under water
-breaking kidney stones
-cleaning jewellery
-detecting cracks in machinery
how to break kidney stones or clean jewellery with ultrasound:
the vibrations caused by the ultrasound shake apart the dirt or kidney stones, breaking them up
steps of ultrasound to see foetuses
- place an ultrasound device (which can transmit and receive ultrasound waves)
onto the woman’s belly - fire ultrasound waves towards the foetus
- every time the ultrasound waves pass from one medium to another (eg: tissue to fluid surrounding foetus) some waves are reflected back to the device at the boundary
- the time taken for the waves to leave a source and return to a detector is measured, the depth of the boundary can be determined
- these echoes are processed by a computer to produce a live image of the foetus
why is ultrasound used for foetal scanning?
-no mutations
-no risk of cancer
how to calculate distance with ultrasound
use DST square then divide by 2 (as that’s the distance there and back, not to there only)
how ultrasound is used to find faults in machinery:
because the machine is fully solid, ultrasound should only be reflected at the start and end of the object, as that’s when the mediums change, if the ultrasound reflects earlier there must be a crack
echo sounding
high frequency sound waves are emitted into deep water to calculate distances
what is echo sounding used for?
detect objects in deep water
echolocation
the process of using reflected sound waves to find objects
uses of infrasound
-communication between animals
-predicting natural events
-investigating the internal structure of the planet
how is sonar used in boats?
to detect the depth of a seabed or to finds shipwrecks, submarines & shoals of fish
when you calculate distance with sonar, what must you do?
divide by 2
structure of the earth
crust = outer layer of earth
mantle = thickest layer of earth (semi-
molten rock/magma)
outer core = liquid layer
inner core = hottest part of the earth, solid, made up of iron and nickel
s waves for the earth’s structure
-s waves only travel through solids
-s waves aren’t detected on the opposite side of the earth -> that the mantle has solid properties, but the outer core must be liquid
p waves for earth’s structure
-p waves can travel through solids and liquids
-p waves are detected on the opposite side of the earth
-refractions between layers cause two shadow zones, where no p waves are detected
-the size and positions of these shadow zones indicate there is a solid inner core
pinna
outer ear that acts like a funnel & sends the sound into the ear canal
ear canal
a tube running from the outer ear to the middle ear
ear drum
a tightly stretched membrane at the end of the ear canal that vibrates when hit by sound waves
ossicle
3 small bones in the middle ear (hammer, anvil, stirrup)
cochlea
-small circular tube filled with liquid in the inner ear
-vibrations from the ossicle create waves in the cochlear fluid and convert the sound vibration into liquid vibration
-the cochlea contains many hairs and when the fluid in the cochlea moves, it moves these hairs, creating nerve signals that get sent through the auditory nerve to the brain
auditory nerve
the nerve that carries impulses from the inner ear to the brain, resulting in the perception of sound
where can lower frequencies be detected in the cochlea?
the apex
where can higher frequencies be detected in the cochlea?
the base
