Waves Flashcards
wave definition
disturbances that transmit energy from one place to another without transferring matter
propagation direction definition
direction of travel of a wave
direction energy is transported
longitudinal wave definition
disturbance cause by wave is felt in propagation direction
transverse wave definition
disturbance caused by wave felt perpendicular to propagation direction
amplitude definition
A
maximum displacement of a wave from resting point
frequency definition
f
number of waves passing a point per second
measured in Hz
wavelength definition
lambda
length of full cycle of a wave
distance between the same points on 2 waves
shape of transverse waves
peaks and troughs above and below equilibrium
oscillated perpendicular to propagation direction
examples of transverse waves
EM waves
waves on guitar string
S-waves
shape of longitudinal waves
vibrates in propagation direction
areas of high density (compression) as oscillating particles forced close together, areas of low density (rarefraction)
examples of longitudinal waves
sound waves
P-waves
S-waves vs P-waves
both mechanical waves
S-waves travel transverse through solid rock only, slower
P-waves travel longitudinal through solid + liquid rock, faster
wave equation
wave speed(m/s) = frequency(Hz) x wave length(metres) v = f x lambda
period definition and formula
T
how long it takes to complete 1 oscillation
T = 1/f
reflection definition
change in direction of a wave without change of speed, wavelength or frequency
law of reflection
angle of reflection = angle of incidence
refraction definition
change in direction of a wave as it travels from one medium to another with a different refractive index
greater difference in refractive index = greater change in speed and direction
how refraction occurs
waves meet new medium at angle to boundary (not perpendicular to boundary or else no change in direction, just less wave speed and wavelength)
enters medium w/ greater refractive index = bends toward normal
enters medium w/ lower refractive index = bends away from normal
how dispersion occurs and why
white light shone through a prism at an angle to the boundary
different wave lengths refracted by different amounts
splits into difference colours
sound type of wave
longitudinal
mechanical
sound features
requires medium to travel through
travels fastest through denser (solid) mediums
causes air molecules to vibrate
pitch
depends on frequency of sound waves
high-freq sound wave = high pitch, short wavelength
low-freq sound wave = low pitch, long wavelength
range of ultrasound
> 20kHz
range of infrasound
< 20Hz
volume
depends on amplitude of sound waves
why pitch and volume are independent
frequency and amplitude are independent
echo definition
delayed reflections one hears after an initial sound has passed
how echoes occur
noise made
some of sound waves travels first to the ear and registered by brain
some of sound waves travels away from source, reflected off surface and heard by ear and registered by brain with time delay
why sound waves change in direction due to refraction hard to hear
sound waves spread out too much
electromagnetic waves summary
all transverse waves
spectrum divided into 7 regions based on wavelength/frequency
all have same speed
speed of light in vacuum
3x10ms^-1
radio waves defined as
longest wavelength of EM spectrum
wavelength > 10cm
radio waves main uses
broadcasting
communication
e.g. radio/TV/mobile phone signals
shortwave radio signals length + uses
wavelength: 10-100m
long distance communication (TV, FM)
signal bounces off ionosphere due to short wavelength
longwave radio length and uses
wavelength: 1-10km
travel long distances because can diffract around Earth’s curved surface
diffraction definition
involved change in direction of waves as they pass through an opening or around a barrier in their path
results in direction of wave changing + wave spreading out perpendicular to propagation direction + transmitting over greater area
order of EM waves (wavelength longest to shortest)
radio waves microwaves infrared radiolarian visible light ultraviolet light x-rays gamma rays
energy, wavelength and frequency
shorter wavelength = faster frequency (due to wave equation)
faster frequency = more energy
microwaves in TV
transmitters produce microwaves able to pass through Earth’s atmosphere to satellites in space
bounces signal down to desired locations, picked up by satellite dish
microwaves in mobile phone signals
signal from phone travels to nearest transmitter as microwaves then to other phones
microwaves in cooking food
penetrates few centimetres into food before being absorbed by water molecules
water molecules vibrate (heats up), cooks food by conduction and convection
microwaves dangers
frequency when used in communication too low to damage tissues
can cause internal hearing of body tissues with higher frequencies, causes burns
how microwave ovens are safe
metal cases
screens over glass doors reflects and absorbs microwaves to prevent them from escaping
infrared radiation features
wavelength: 700nm to 1mm
infrared wavelength
700nm to 1mm
how IR cameras work
good for producing images in the absence of visible light
detect IR to produce an image
more IR emitter = warmer region
uses of IR
monitoring temperatures heating food security cameras night-vision automatic doors short distance communication (remote controls) optical fibres
how optical fibres work
thin rods of high quality glass transmit information as infrared signals
repeatedly and rapidly reflects infrared from one end to the other
greenhouse effect
Sun’s rays enters Earth’ atmosphere
some pass through outer atmosphere, some reflected back out into space
rays reach surface, some partially reflected or partially absorbed depending on object they incident on
surface of Earth radiates IR back into space
greenhouse gases in atmosphere absorb some of IR instead of reflecting it back to space
gases conduct, convect, radiate heat to surroundings
greenhouse gases examples
carbon dioxide
water vapour
methane
visible light wavelength
300nm to 700nm
how sight works
visible light reflected off object into eye
lens refracts visible light focused onto retina
retina sends messages to brain via optic nerve to be interpreted
what happens if intensity of incident light too high
if intensity of incidence light too high, causes blindness
UV light wavelength
100nm to 400nm
why we tan
skin absorbs UV light
turns darker to absorb more UV light to prevent it from reaching deeper tissue
UV light uses
detect forged bank notes (real ones have fluorescent ink)
security pens
treatment of skin conditions, sterilise medical equipment
fluorescent lamps
dangers of overexposure to UV light
eye problems
damage DNA, causes cancer
X-rays wavelength
0.01nm to 10nm
X-rays uses
investigate internal structure of objects passes through less dense objects, absorbed by denser objects detect bone fractures airport security (scan luggage)
gamma rays wavelength
smallest wavelength
highest energy
gamma rays uses
sterilise food+medical equipment
diagnosis + treatment of cancer
X-rays/gamma rays dangers
high ionising ability
can damage greater number of cells
can cause tissue damage and cancer
