waves Flashcards
waves can either be
transverse or longitudinal
define transverse waves
the direction of oscillation is perpendicular to the direction of energy transfer
examples of transverse waves
electromagnetic waves like light and microwaves, ripples on a water surface
define longitudinal waves
the direction of oscillation is parallel to the direction of energy transfer
examples of longitudinal waves
sound waves travelling through air
difference between transverse and longitudinal waves (medium)
all longitudinal waves require a medium to travel through (gas, liquid, solid) whereas some transverse waves can travel through a vacuum e.g., electromagnetic waves
what do all waves do
they transfer energy from one place to another
e.g., ripples transfer kinetic energy
sound waves transfer sound energy
describe evidence that for ripples on a water surface and for sound waves in air, it is the wave and not the water or air itself that travels
ripples on a water surface: if you place a floating duck on a water wave (transverse) the duck will bob up and down but will not move from side to side
sound waves in air: if you use a slinky to model a longitudinal wave and mark a fixed point on the slinky, it will move side to side but does not travel through the medium
what is the top of the wave called
the peak or the crest
what is the bottom of the wave called
the trough
define the amplitude of a wave
the maximum displacement of a point on a wave away from its undisturbed position
define the wavelength of a wave
the distance from a point on one wave to the equivalent point on the adjacent wave
define the frequency of a wave
the number of waves passing a point each second
define the wave speed of a wave
the speed at which the energy is transferred (or the wave moves) through the medium
define the period of a wave
the time taken for one wave to pass a point
method for measuring speed of sound waves in air
1) person A has cymbals, person B has timer
2) make them stand 500m apart
3) person A crashes cymbals together; person B starts stopwatch when they see person A crash cymbals and stops stopwatch when they hear crash of cymbals
4) calculate speed of sound waves by doing S=D/t
issues with the experiment for measuring speed of sound waves in air and how to resolve them
- different people have different reaction times, giving way for inaccuracies
to overcome this, we can use a large number of observers with timers and calculating a mean - it is only a very short space of time between seeing cymbals crash and hearing them, making it very difficult to press stopwatch at correct times
increasing distance between the people can reduce this problem
what can waves do between two different materials
at the boundary, they can be reflected, absorbed or transmitted
what can sound waves travel through
solids, causing vibrations in the solid
how are the limits of human hearing restricted
within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound; the conversion of sound waves to vibrations of solids works over a limited frequency range, thus restricting the limits of human hearing
range of normal human hearing
20Hz to 20kHz
frequencies outside this range do not cause the ear drum to vibrate
how do microphones detect sound waves
the sound waves cause the microphone to vibrate, and microphones transfer these vibrations into an electrical signal by detecting the sound waves’ frequency and amplitude as the waves hit the paper cone, causing it to vibrate forwards and backwards
what do sound waves move faster in and why
sound waves move faster in solids than in gases because they are longitudinal mechanical waves rather than being electromagnetic, so because particles are closer together in solids, vibrations can be passed on more easily between them
what happens when waves move from one medium to another
their speed can change; when wave speed changes as waves pass from one medium to another, wavelength must also change - that is because the frequency never changes (bc that would mean we’re not abiding by the law of conservation of energy)
therefore increasing wave speed would increase wavelength, and decreasing wave speed would decrease wavelength
what does a cathode ray oscilloscope do and what’s an issue with using one
it allows us to see the features of sound waves; the only issue is that it represents sound waves as transverse waves which is incorrect
cathode ray oscilloscope wave property meanings
- frequency controls pitch; high frequency means high pitch and vice versa
- amplitude controls volume; high amplitude means loud volume and vice versa
define echo
a reflected sound wave
what is ultrasound
sound waves with a frequency higher than the upper limit of hearing for humans (i.e., >20kHz)
what is ultrasound
sound waves with a frequency higher than the upper limit of hearing for humans (i.e., >20kHz)
what happens to ultrasound waves at a boundary
they are partially reflected when they meet a boundary between two different media (with different densities)
how can you determine how far away a boundary is
use the time taken for the reflections to reach a detector, and multiply it by the speed of the ultrasound wave (which is shown on the device)
this is the distance = speed x time equation
what are ultrasound waves used for
- medical imaging; e.g., internal organs, prenatal scanning
- industrial imaging; e.g., detecting hidden defects like cracks or air bubbles
condition for using ultrasound waves for producing images of internal organs
the organ cannot be surrounded by bone, otherwise it would absorb the ultrasound wave and wouldn’t be detected by the scanner
pros of ultrasound waves over x-rays
- ultrasound is much safer than x-rays because it is non-ionising unlike x-rays, therefore it doesn’t increase the risk of mutations and cancer
- ultrasound can distinguish between two different types of soft tissue, unlike x-rays which would just penetrate through both
why can ultrasound be used for industrial imaging
because there is a difference in density between hidden defects like air bubbles and the rest of the material, so partial reflection takes place at the boundary
state of the layers of the earth
mantle - solid
outer core - liquid
inner core - solid
what did the study of seismic waves aid
they provided new evidence that led to discoveries about the structure of the Earth which is not directly observable
how are seismic waves produced
they’re produced by earthquakes; when an earthquake occurs due to a sudden movement between tectonic plates in the earth’s crust, seismic waves are emitted, which carry energy away from the earthquake
what happens after seismic waves are emitted
they can pass through the earth and be detected by seismometers; the patterns of these waves give us the information about the internal structure of the earth
types of seismic waves
P-waves (primary waves)
S-waves (secondary waves)
PLease SiT (PLST)
P Longitudinal, S Transverse
what type of waves are the seismic waves
- P-waves are longitudinal seismic waves
- S-waves are transverse seismic waves
what can the seismic waves pass through
- P-waves can travel at different speeds through both solids and liquids
- S-waves can only travel through solids
S- waves Solids (way to remember)
what seismic wave travels faster
p waves travel faster than s waves
define echo sounding
the use of high frequency sound waves to detect objects in deep water and measure water depth
define electromagnetic waves
transverse waves that transfer energy from the source of the waves to an absorber
what do electromagnetic waves form
they form a continuous spectrum
how do electromagnetic waves travel
they travel at the same velocity through a vacuum (space) or air
how are electromagnetic waves grouped
in terms of their wavelength and their frequency
order of electromagnetic waves
Red - radio waves
Men - microwaves
Invaded - infrared
Venus - visible light
Using - ultraviolet
X-Ray - x-ray
Guns - gamma rays
electromagnetic wave spectrum from short to long wavelength
gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves, radio waves
electromagnetic wave spectrum from low to high frequency
radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays
what electromagnetic wave(s) do our eyes detect
our eyes only detect visible light and so detect a limited range of electromagnetic waves
what are radio waves produced by
oscillations in electrical circuits
what happens when radio waves are absorbed
they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical current
what do gamma rays originate from
changes in the nucleus of an atom
what do changes in atoms and the nuclei of atoms result in
electromagnetic waves being generated or absorbed over a wide frequency range
what electromagnetic waves can have hazardous effects
ultraviolet waves, x-rays and gamma rays on human body tissue
what do the hazardous effects from electromagnetic waves depend on
the type of radiation and the size of the dose
define radiation dose
a measure of the risk of harm resulting from an exposure of the body to the radiation
unit of radiation + conversion
sieverts (Sv)
1000 millisieverts (mSv) = 1 sievert (Sv)
effect of ultraviolet waves on the body
they can cause skin to age prematurely and increase the risk of skin cancer
effect of x-rays and gamma rays on the body
they are ionising radiation that can cause the mutation of genes and cancer
practical applications of radio waves and how its suitable
television and radio
- they can easily pass through air
practical applications of microwaves and how its suitable
satellite communications, cooking food
- microwaves are absorbed by water molecules in the food; the energy carried by the waves turns into thermal energy in the food
practical applications of infrared waves and how its suitable
electrical heaters, cooking food, infrared cameras
practical applications of visible light waves and how its suitable
fibre optic communications
practical applications of ultraviolet waves and how its suitable
energy efficient lamps, sun tanning
practical applications of x-rays and gamma rays and how its suitable
medical imaging and treatments
how does a lens form an image
by refracting light
describe how a convex lens works
parallel rays of light are brought to a focus a the principal focus
define the focal length
the distance from the lens to the principal focus
what do ray diagrams show
the formation of images by convex and concave lens
images produced by convex lens vs concave lens
convex lens; can either be real or virtual
concave lens; always virtual
define specular reflection
reflection from a smooth surface in a single direction
define diffuse reflection
reflection from a rough surface causes scattering
how do colour filters work
by absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour)
how is the colour of an opaque object determined
it’s determined by which wavelengths of light are more strongly reflected; wavelengths that are not reflected are absorbed. if all wavelengths are reflected equally the object appears white; if all wavelengths are absorbed the object appears black
define transparent or translucent objects
objects that transmit light
what objects absorb infrared radiation and under what conditions
all bodies (objects), no matter what temperature, emit and absorb infrared radiation. the hotter the body, the more infrared radiation it radiates in a given time
define a perfect black body
an object that absorbs all of the radiation incident on it. a black body does not reflect or transmit any radiation; since a good absorber is also a good emitter, a perfect black body would be the best possible emitter
how are changes in velocity, frequency and wavelength are inter-related in the transmission of sound waves
velocity of sound is directly proportional to the wavelength, thus, if the velocity of sound doubles when it travels from one medium to another, its wavelength also doubles; the frequency of sound depends upon the source of sound, not the medium of propagation so it does not change.
what is the property of a body at constant temperature
it is absorbing radiation at the same rate as it is emitting radiation
when does the temperature of a body increase
when the body absorbs radiation faster than it emits radiation
what factors does the temp of the earth depend on
- the rates of absorption and emission of radiation
- reflection of radiation into space
