M4 Waves - Part 1 Flashcards
features of waves, phase difference, EM waves, polarisation, intensity
define wave
periodic disturbance in a material or space
each particle vibrates about a fixed position
energy is transferred outwards from the source of the wave
what are progressive waves
an oscillation that travels through matter, transferring energy.
when traveling through a medium, particles move from equilibrium position to a new position.
the displaced particle experiences a restoring force from neighboring particles and returns to its original position.
what types of waves are transverse and longitudinal
progressive
define transverse waves
the direction of vibration is at 90 degrees to the direction of energy transfer
these have crests and troughs
give examples of transverse waves
EM waves
waves on water
s waves in earthquakes
define longitudinal wave
the direction of vibration is parallel to the direction of energy transfer. these have compressions and rarefactions
give examples of longitudinal waves
sound waves
p waves in earthquakes
define mechanical wave
give examples
these waves require a material/medium to transfer through
produced by oscillation of particles in a medium
eg. sound or water
define electromagnetic waves
these waves require no medium and so can transfer energy through a vacuum
produced by acceleration of charged particles
define amplitude
the maximum displacement of the wave in either the positive or negative direction (from equilibrium position)
unit is m
define displacement of a wave
distance of a point from the equilibrium position in a particular direction (vector)
has positive or negative direction
define wavelength
Distance between 2 points in phase on adjacent waves
eg. distance between two successive crests
define frequency
number of oscillations/vibrations (at a point) per unit time
define period
time taken to produce one complete wave
symbol = T
define wave speed
distance travelled by a wave per unit time
symbol = v
define phase difference
difference between displacements of particles along a wave
a complete wave = 360 degrees or 2π radians
in phase = phase difference of 0
units = degrees or radians
derive v = fλ
s = d/t distance = wavelength time = period s = wavelength / period period = 1/frequency s = wavelength / 1 / frequency s = wavelength X frequency s = v v = f X λ
classify the following waves:
a) sound
b) light
c) water
d) x-rays
e) microwaves
a) sound = longitudinal and mechanical
b) light = transverse and electromagnetic
c) water = transverse, sometimes longitudinal and mechanical
d) x-rays = transverse and electromagnetic
e) microwaves = transverse and electromagnetic
what are all the basic wave properties of EM waves
reflection refraction diffraction polarisation interference energy transference
what is the speed of EM waves
3 X 10^8 ms^-1
which of radio waves or gamma rays has the longest wavelength?
radio
what is the wavelength of radio waves
10^-1 - 10^6
what is the wavelength of microwaves
10^-3 - 10^-1
what is the wavelength of infrared waves
7 X 10^-7 - 10^-3
what is the wavelength of visible light waves
4 X 10^-7 - 7 X 10^-7
what is the wavelength of ultraviolet waves
10^-8 - 4 X 10^-7
what is the wavelength of x-rays
10^-13 - 10^-8
what is the wavelength of gamma rays
10^-16 - 10^-10
on a EM wave, how do the magnetic and electric field relate
they are perpendicular to each other
radio waves
what can it penetrate through?
what are the uses?
pass through matter
radio transmissions
microwaves
what can it penetrate through?
what are the uses?
mostly pass through matter but causes some heating
infrared
what can it penetrate through?
what are the uses?
absorbed by matter, causing it to heat up
heat detectors, night vision cameras, remote controls and optical fibres
visible light
what can it penetrate through?
what are the uses?
absorbed by matter, causing heating
human sight, optical fibres
ultraviolet
what can it penetrate through?
what are the uses?
absorbed by matter, cause some ionisation
sunbeds, security marks that show up under UV
x-rays
what can it penetrate through?
what are the uses?
mostly pass through matter, cause ionisation as they pass
see the damage to bones and teeth, airport security scanners, kill cancer cells
gamma rays
what can it penetrate through?
what are the uses?
mostly pass through matter, cause ionisation as they pass
irradiation of food, sterilisation of medical instruments, kill cancer cells
what waves does polarisation effect
transverse waves
describe an experiment to demonstrate the polarisation of microwaves
Place microwave transmitter and receiver facing each other
Rotate one of them through 90 degrees about axis
Observe signal fall to zero from initial high value on meter monitoring output of the receiver
Use 2 polarising filters and rotate from parallel to crossed
how is polarisation used in microwave ovens
unpolarised rays of microwaves are prevented from leaving the microwave by a fine metal grid covering the door
this grid absorbs both horizontal and vertical oscillations of the microwaves
draw a diagram which represent unpolarised light
a line with dots with arrows going up and down
draw a diagram to show vibrations of E-field in unpolarised light
a dot with arrows going out in lots of directions
draw a diagram of how a polaroid is used when the first one to the light is verticle and the next one is horizontal
unpolarised light goes in the vertical polaroid and keeps going through but is stopped by the horizontal polaroid
the vertical polaroid is called the polariser
the horizontal polaroid is called the analyser
draw a diagram to show polarised light by relfection
look it up
pg 10 of 1st waves booklet
what is plane polarised light
when all of the waves are in the same plane
applies to transverse waves
why is light from a candle unpolarised
every wave is aligned in a random and different plane
what is reflection
what is the law of reflection
all waves reflect off a surface
for a plane surface , the angle of reflection = angle of incidence
normal is drawn perpendicular to the surface
what is refraction
if waves goes through a boundary, their speed and wavelength changes
if they are incident at a non-zero angle to the boundary then they will change direction
what is diffraction
when does max diffraction happen
waves that pass through a gap or around an obstacle will spread out
maximum diffraction happens when the gap is similar in size to the wavelength of the wave
what is the intensity of a progressive wave
the power passing through a surface per unit area
unit is Wm^-2
how does intensity and distance relate
intensity decreases with distance
I is directly proportional to 1/r^2
when they give a distance in a question it means the radius
how does intensity and amplitude relate
decreasing amplitude means reduce in average oscillating speed of particles
I is directly proportional to A^2
eg. doubling the amplitude means 4X the intensity
what are the proportionalities you need to know for intensity
I directly proportional 1/r^2
I directly proportional A^2
if the distance from earth to the sun is 1.5 X 10^11 m and the intensity is 1400 Wm^-2 then what is the power
I = P / A P = AI A = 4πr^2 = (4π(1.5 X 10^11)^2) X 1400 = 4X10^26 W
