WAVES Flashcards
what two forms can waves take?
Longitudinal and transverse
what is longitudinal waves
waves which, the oscillations are parallel to the direction of travel
what is a transverse wave
a wave which will oscillate perpendicular to the direction of travel
what are progressive waves
waves which transfer energy from a source
what is phase difference
two points have exactly the same pattern of oscillation are said to be in phase.
how do you use an oscilloscope to find the frequency of a wave
-displays a voltage-time signal, can measure the from a signal generator, representing displacement over time.
how do you work out the speed of a wave?
v=fλ
calculate intensity
intensity= power/area
power= energy/time
calculate intensity if power spreads out in all directions
power/ 4πr^2
define intensity
that rate at which energy is transferred from one location to another as the wave travels through space.
what is the relationship between intensity and amplitude
I=a^2
because the amplitude of a wave decreases as it moves away from a source.
what is refraction
occurs when a wave moves from one medium to another, when they have different densities. the wave will change speed and maybe direction
define diffraction
is the spreading out of a wave after passing around an obstacle or through a gap
define interference
is the addition of two or more waves (superposition) that results in a new wave pattern
what are properties of em waves
-travel through vacuum
-travel at speed of light in vacuum
-can be polarised
-demonstrate interference
what is the λ of radio
10^-1 to 10^4
what is the λ of microwave
10^-4 to 10^-1
what is polarisation
when the oscillations of the field and direction are confined to a singular plane
how can we observe the polarisation of microwaves
wave transmitter- transmits unpolarised waves
place metal grill in front of wave, with horizontal grills
microwave receiver picks up signal- connected to ammeter
what is malus law
when you have two polarising filters, when you rotate the second one at an angle of ø to the first, the amplitude will be Acosø.
what is a refractive index
a way to measure how the speed of a wave will change when entering a material of different density.
the speed will decrease as it enters from lower refractive index to higher index
calculate refractive index
n=c/c in the material
what is snells law
n1 x sinø1=n2 x sinø2
or nsinø=constant
what is the diffraction grating equation
n lamda=dsinø
n is the order
ø is the angle to the order n
what is total internal reflection
is the result of both reflection and refraction. we observe it when light travels from a material of higher to lower refractive index. Initially at an angle lower than the critical angle refraction will occur and there will be weak reflected ray
what is the critical angle
the greatest angle at which a ray of light, travelling in one transparent medium, can strike the boundary between that medium and a second of lower refractive index without being totally reflected within the first medium.
calculate the critical angle
sinC=1/n1
C is the critical angle
n1 is the material of higher refractive index
if intensity increases by a factor of 2, what does amplitude increase by?
root 2
if an amplitude increases by two, what does the area underneath increase by?
4
what is the relationship between amplitude and intensity
a ^2 prop I
what is the refractive index
the ratio of the speed of light in a vacuum to the speed of light in the material
how do you calculate the amplitude of a wave passing through an angle of polaroid
A=AoCosø
equation for microwave intensity passing through metal bars in relation to angle
IoCos^2ø=I
what is snells law (air)
sin i/sin r =n of denser material
