4.4 Flashcards
amplitude
maximum displacement of a wave from its rest position
ferquency
number of complete wave cycles that occur in one second
period
time taken for a wave peak to travel the distance of one wavelength(time taken for one oscillation)
progressive wave
a type of wave that travels through a substance or space
transverse wave
type of wave in which oscillations occurs at rights angles to the direction of wave propagation
longitudinal wave
a type of wave in which oscillations occur parallel to the direction of wave propagation (cant travel through a vacuum).
what is path difference measured in
n λ (1 λ= 1 wavelength)
what is phase difference measured in
π radians (2πvradians = 1λ)
principal of superposition
when 2 or more waves meet the total displacement at any one point is equal to the sum of the displacements that each individual wave would cause
interference
when two waves interact with each other
coherence
when waves have constant phase difference
constructive interference occurs when
the path difference between coherent sources is nλ where n is an integer
cancellation occurs when
the path difference between two coherent sources is nλ/2
stationary/ standing wave
the superposition of two progressive waves with the same wavelength moving in opposite directions energy is stored
node
point on a stationary wave where no displacement occurs
anti node
point of a stationary wave where maximum displacement occurs
em spectrum
radio, microwaves, visible light, uv, x-rays, gamma
physical waves
progressive waves that transfer matter/particles ie sound waves or water waves
electromagnetic waves
progressive waves that transfer energy without transferring matter
properties of em waves
can travel through a vacuum, posses both a magnetic and electrical waves at right angles to each other, all travel at 2.98x10^8 m/s in a vacuum, all transverse, all can be reflected refracted and diffracted, all demonstrate interference, all can be polarized
polarized wave
a plane polarized wave oscillates in only one plane happens only in transverse waves
what are polarizing filters made of
crystalline materials that absorb waves
applications of polarized light
tv signals and radio signals are polarized so transmitting and receiving aerials must be aligned, 3d glasses, stress analysis of plastic
malus’s law
the light passing through a perfect polarizer can be found by the equation= I=Imaxcos^2θ
refraction
the change in direction a light ray undergoes when it enters a medium with a different optical density
why does refraction occur
light travels at different speeds in materials with different optical densities. the change in direction occurs due to the change in speed
in what direction does light bend
towards the normal as it slows, away from the normal as it speeds up
how to find the refractive index of a material
n=c/v
snells law
n1sin1 θ1=n2sin2 θ2
critical angle
when the angle of incidence = the critical angle light will travel along the boundary of the secondary medium it will be refracted by 90 degrees
total internal reflection
when the angle of incidence exceeds the critical angle light is reflected in the material
young’s double slit equation
λ=(ax)/d d=distance from slits to screen, x=distance between adjacent maxima, a=slit sepparation
diffraction
the spreading out/bending of light waves as they pass through a gap or around an obstacle
when is diffraction greatest
when the width of the aperture=wavelegnth
diffraction grating
a place with many closely spaced parallel slits that produces spaces interference pasterns as a result of superposition
why use diffraction gratings not a double slit arangement
the pattern is much clearer making it possible to calculate the wavelength
diffraction grating equation
nλ=dsinθ d=slit sepparation
how to find the maximum number of orders
substitute θ=90
Fundamental mode of vibration
In this mode the length of the string is 1/2 the wavelength. This produces the lowers possible frequency the 1st harmonic
2 ways to graph waves
- “snapshot of wave” shows displacement (y axis) vs distance travels (x axis)
- displacement against time
How to represent longitudinal waves graphically
Pressure against position
How to find the period of a wave with an oscilloscope
Distance between peaks x time base setting
Uv-a
99% of uv
Causes tanning
3.15-4 x10-7 meters (wavelength)
Uv-b
Causes skin cancer and sunburn
2.8-3.15x10-7 m wavelength
Uv-c
Filtered out by atmosphere
1-2.8x10-7 m wavelength
