Chapter 11 - Waves 1 Flashcards
what is a progressive wave
“a progressive wave is a transfer of energy but not matter from one place to another through an oscillation”
what is the key feature of a longitudinal wave
oscillations
squishes etc.
oscillation occur parallel to the direction of travel
has compressions and rarefaction’s
a full wavelength is the distance between two compressions etc.
what are the key features of a transverse wave
oscillations occur perpendicular to the direction of travel
there are peaks and troughs where one full wavelength is the distance between two troughs or two peaks
how do particles move from their equilibrium positions in the two types of wave
in a transverse wave the amplitude shows the greatest distance from their equilibrium positions that they move
in a longitudinal wave the particles vibrate about their equilibrium positions but do not move
what is the wave equation
v = f x (lambda)
relationship between period and frequency
f = 1/t T = 1/f
define displacement, symbol and unit
s, m
distance from the equilibrium position in a particular direction (vector)
define amplitude, symbol and unit
A,m
maximum displacement from equilibrium position
define wavelength, symbol and unit
(lambda), m
minimum distance between two points in phase on adjacent waves
define period, symbol and unit
T,s
the time taken for one complete oscillation or wavelength
define frequency, symbol and unit
f, Hz
the number of wavelengths passing a set point per unit time
define wavespeed, symbol and unit
v (or c), ms^-1
the distance traveled by the wave per unit time
what happens in reflection
- occurs when a wave changes direction at a boundary
- angle of incidence = angle of reflection
- frequency and wavelength do not change
what happens in refraction
- occurs when a wave changes direction as it speeds up or slows down when it moves from one medium to another (based on refractive index)
- slows down = moves towards normal
- speeds up = moves away from normal
- refraction affects wavelength but not frequency because wavespeed changes
what is diffraction
when waves pass through a gap or travel around an obstacle they spread out
what changes during diffraction
nothing
wavelength, frequency and speed remain the same
what affects diffraction
size of gap relative to wavelength
when wavelength is equal to the size of the gap there is maximum diffraction
what is a polarised wave
a polarised wave is one which only oscillates in one direction
this means it is only in one plane so is plane polarised
what does light from an unpolarised source have
light from an unpolarised source has many planes of oscillation but all are at 90 degrees to the direction of travel
can longitudinal waves be polarised
no they already are, they only have oscillations in one plane (the direction of movement)
define intensity
“the radiant power per unit area of a progressive wave where”
I = P/A
intensity equation
I = P/A
intensity (Wm^-2) = power (W) / area (m^2)
what happens when a wave spreads out from its source (proportionality)
When a wave spreads out from its source, the power is spread over a larger area so intensity decreases
due to the equation for S.A. of a sphere 4pir^2
you end up with I=k/r^2
intensity is inversely proportional to the radius squared
what happens to intensity when amplitude changes
when amplitude decreases the particles oscillate less giving less kinetic energy and because Ek is proportional to V^2
intensity is proportional to amplitude^2
do EM waves need a medium
no
what are EM waves
EM waves are transverse waves which have electric and magnetic components which oscillate and 90 degrees to both each other and the direction of travel
can EM waves be reflected, refracted, diffracted and plane polarised
yes
order of EM spectrum in decreasing wavelength/increasing frequency
radio waves = >10^6 –> 10^-1 m
microwaves = 10^-1 –> 10^-3 m
infrared = 10^-3 –> 7x10^-7 m (700nm)
visible light = 700nm –> 400nm
UV = 4x 10^-7 –> 10^-8 m
X rays = 10^-8 –> 10^-13
Gamma rays = 10^-10 –> anything smaller
what are most naturally occurring waves
unpolarised
what do polarising filters do
they vary depending on wavelength but they only let one polarisation of light pass through
what are some uses of polarising filters
3D films, photography etc.
what happens with 2 polarising filters
the intensity of light will change from full to nothing as they go in and out of phase
how to calculate refractive index from speed values
n = C1/C2
n is refractive index, C1 is speed of light in first medium, C2 is speed of light in second medium
what is snells law
n1 sinX = n2 sinY
typical refractive index values
vacuum and air = 1 water = 1.33 olive oil = 1.47 glass = 1.5 diamond = 2.42
what are the two conditions for TIR
- going from a higher refractive index to a lower refractive index
- the angle to the normal is > critical angle
calculating critical angle
n1 sinC = n2 sin(90)
Define phase difference
The difference in displacement of particles on a wave or on different waves
what features of EM waves remain constant throughout the spectrum
- all travel at the speed of light in a vacuum
- all are transverse
- all can be plane polarised
what features of EM waves change throughout the spectrum (other than frequency and wavelength)
- the human eye’s sensitivity to the light
- how they diffract for a given gap size
- the heating effects of infra-red vs others
