Wave 1 Flashcards
Progressive Waves
progressive waves transfer energy from one place to another, but not matter
Phase difference
difference in displacement of a particle along a wave
Using an osciliscope to determine wave frequency
the screen shows a graph of p.d against time for any signal fed to it.
Timebase
horizontal squares on the oscilisope screen which represents a certain time interval eg 10ms/cm
what is a wave profile
displacement distance graph
wavefront
line joining points of the wave which are in phase.
Easier to think of as peaks of the wave.
reflection
angle of incident = angle of reflection
wavelength and frequency is the same
refraction
n1 sin θ1 = n2 sin θ2
where n is the refractive index
θ is the angle from the normal
n = c/v for em waves
velocity propotional to θ
n inversely propotional to θ
partial reflection
when a wave reflect there’s always some reflection off the surface
Diffraction
property unique to waves
occurs when passing through a gap or travel around an obstacle, and they spread out
when differacted speed, wavelength and frequency do not change
more diffraction occurs when the gap is about the same size as wavelength of the wave
Polarisation
means particle ocsilate along one direction only
plane polarised whena wave is confined to one single plane
only transverse waves
partial polarisation
Intensity
intensity of a progresive wave is the radiant(radiation) power passing through a surface per unit area.
measured in W/m^2
I = P/A
what is the power distnace r from a source
power spread uniformaly in all directions from a source.
so the area of the power would be of a sphere
I = P/A = P/( 4 π r^2 )
Intensity and Amplitude
I ∝ A^2
in the em spectrum why are there overlapse between x ray and gamma ray
they are classified by thier origin,
X rays are emitted from fast moving electrons whereas gamma rays are from unstable atomic nuclei
polarising filters
polarising filters called polarisers can be used to polarise which only allows wave in one orientation to go through
polarisation of light
two polarisers
first one polarises the light
second one (often called analyser) rotates and intensity decresases, at 90 degrees to the first intensity falls to zero.
polarisation of microwaves
instead of using a polaroid filter a metal grille is used
refractive index
n = c/v
conditions for total internal reflection
light must be traving through a medium with higher refractive index as it stricks with one iwht a lower one
angle which it strikes needs to be ablove the critical angle
formula for total internal reflection derivation
from snells law
n1 sin θ1 = n2 sin θ2
θ2 = 90 =>
sin θ1 = n2/n1
but its air outside so n2 is 1
sin θ1 = 1/n1
determining refractive index of a material using critical angle
