Section 3 - Waves Flashcards
wavelength λ
distance from one peak to the next
frequency (f)
how many complete waves there are per s (passing a certain point)
measured in Hz (1Hz = 1 wave per second)
amplitude is
height of wave (from rest to crest)
speed (v)
how fast wave goes
period (T)
time in s it takes for one complete wave to pass a point
frequency formula
f = 1/T
wave speed (m/s) formula
frequency (hz) x wavelength (m)
v = f x λ
transverse waves
the vibrations are at 90º to the direction energy is transferred by the wave
/\/\/\/\/\/\/\
examples:
- light and EM waves
- slinky spring
- waves on strings
- ripples in water
longitudinal waves
vibrations are along same direction as the wave transfers energy
lll l l l ll l l l l ll llll l l ll l l lll lllllll ll l l l l ll l l l ll
compressions and rarefactions
exampkes:
- sound and ultrasound
- shock waves
slinzy spring when you push end
what waves transfer
- all transfer energy in direction they are travelling
- can also transfer information
wavefronts
imaginary planes cutting across all waves connecting points on adjacent waves vibrating together
distance between wavefronts is one wavelength
when talking ab waves aproching obstace multiple waves in same direction are referd to as wavelengths
doppler effect
waves produced by a source which is moving will have different wavelength than if source were stationary
frequency of a wave from source moving towards you will be higher and wavelength will be shorter than wave froduced by source and viceversa
EM waves
have different properties and grouped depending on wavelength
transverse
Radio (least frequency and largest wavelength)
Micro-waves
infrared
visible light
uv
xrays
gamma
uses of radio waves
1) communication
- long and short wave
- missing details
uses of microwaves
satellite communication and heating food
*
uses of infrared radiation
heating and monitor temperature *
EM Light
colours depend on wavelength (red, organge yellow green blue indigo violet)
travel through optic fibres (carry data long distances as pulses of light)
pulse of light enters at certain angle and is refracted continiously until it emerges at other end
*
visible light uses
optic cables - (telephone internet and mediacal)
photography
*
uv uses
used in florescent light
*
xrays uses
viewing internal structures
*
gamma uses
steralising medical equipement
streilising food (and keeping it fresh)
how can em be harmful
most em pass thrpugh tissues without being absorbed, but they can also
1) cause heating of cells (micro-waves)
2) cause cancerous mutations in living cells (gamma)
higher freq = more energy = more dangerous
dangers of microwaves
internal heating - microwave ovens must be shielded to prevent this *
infrared dangers
internal heating that can cause skin burns
- protect yourself using insulating materials*
UV dangers
damage surface cells and cause blindness
cell mutation/destruction
(ionising - knock electrons off magnets)
sunscreen with uv filters
*
gamma dangers
cell mutation / desturction (also ionising)
leads to tissue damage or cancer
radioactive sources should be kept in lead-lined boxes and exposure as short as possible
*
diffuse reflection
when light reflects from an uneven surface the light reflects off at different angles causing a diffuse reflection
clear reflection
when light reflects from an even surface then it is all reflected in same angle and you get a clear reflection
law of reflection
angle of incidence = angle of reflection
the normal
the perpendicular imaginary line to surface at point of incidence (usually shown as dotted line)
virtual images
form when light rays bouncing off an object onto a mirror are diverging so light from object apperars to be comming from a completely different place
how are waves refracted
travel at different speeds through substances with different densities (em travel slower in denser media, while sound travels faster)
wave hits boundary face on - slows down but carries on in the same direction
wave meets boundary at an angle - top part hits have first and slows down only later followed by bottom part, causing a wave to change direction - be refracted
drawing refracted wave
1) draw boundary & normal
2) incident ray that meets normal at boundary
3) angle between ray and normal is angle of incidence
4) now draw refracted ray.
2 material denser = bends towards normal
angle of refraction smaller than angle of incidence
refractive index
tells you how fast light travells through a material
n = speed of light in a vacuum (c) / speed of light in material (v)
n = c/v
light slows down = high n
snells law
n = sin i (incidence) / sin r (refr)i
critical angle
r = 90º. light is refracted right along boundary
snells law to find critical angles
sin C = 1/n
higher n means lower C
optical fibres
made of plastic/glass consist of central core surrounded by cladding with a lower refractive index
core of fibre is so narrow that light signals always hit boundary at angles higher than C so light is always totaly internally reflected and only stops working if bent too sharply
Prisims
ray of light travels into one prism where it is totally internally reflected by 90º
then travells to another prism and is again totally internally reflected by 90º
ray is now travelling parallel to initial path but at different height
Sound as a wave
will be reflected by hard surfaces (carpets and curtains absorb sound)
refract in diffeent media - denser means they speed up but change in direction is hard to spot
