Waves - Chapter 11 Flashcards
Progressive waves?
An oscillation that travels through matter or a vacuum in some cases
it transfers energy from one place to another without moving particles along the wave
the particles vibrate from an equilibrium position
What is a restoring force?
particles start at an equilibrium position and are displaced before oscillating back to their original position.
Restoring force from neighbouring particles pulls particles back to their starting position.
How to represent longitudinal AND transverse waves with a wave profile?
use a displace time graph - each time the graph reaches 0 it is a compression , then rarefaction then compression
when the wave starts going down, it is a compression
Phase difference
the difference between displacements of particles along a wave or on different waves.
Particles with distances of integer wavelength are in phase e.g 0, 360, 720 or 0, 2pi, 4pi
if the phase difference is 180 or pi/2, then they are completely opposites in displacements and are on anti phase.
displacement symbol and unit and definition
a vector quantity of distance measured from the equilibrium position
symbol s
unit m
amplitude symbol and unit and definition
a measure of the maximum displacement of a particle in a wave from its equilibrium position
unit m
symbol A
wavelength
the minimum distance between two points in phase on a wave
unit m
symbol lambda
Time Period
the time taken for one point on wave to travel one wavelength
unit s
Symbol T
Frequency
The number of wavelengths passing a point per unit time
unit Hz
symbol f
wave speed
the distance travelled by the wave per unit time
unit m s ^ -1
why is f = 1 / t?
Time period is the amount of time for one wavelength to pass
frequency is number of wavelengths that pass per second
so if time period of a wave is 1s , frequency is equal to 1 wave / 1 second = 1
if time period is 0.5s, frequency is equal to 1 wave / 0.5 second = 2
what is the timebase
the time base represents the horizontal length of one square on an oscilloscope. it can be set to a distance as the y axis is set to different voltages
what happens to waves when they are refracted from more to less dense medium
the wave slows down, bends towards the normal, and wavelength decreases
what is diffraction
diffraction is a phenomenon when a wave passes through a gap in an obstacle, the wave spreads out
it is most significant when the wavelength of the gap matches that of the wave
What is polarisation?
polarisation is when a wave is restricted to one plane only
it is unique to transverse waves as longitudinal waves are already oscillating in one plane, that is parallel to the direction of energy transfer
Partial polarisation
when transverse waves reflect of surfaces, they become partially polarised.
more waves are oscillating in one direction but not all of them
Happens to light waves - most waves end up horizontally
What is intensity and its equations
Intensity is defined as the radiant power passing through a surface per unit area
I = P / A
I is inversely proportional to 1/ r^2
I is proportional to amplitude^2
EM waves with wavelengths
radio waves: >10^6 - 10^-1
Microwaves : 10^-1 - 10^-3
Infrared: 10^-3 - 7x10^-7
Visible: 7 x 10^-7 - 4 x 10^-7
Ultraviolet: 4 x 10^-7 - 10^-8
X-rays: 10^-8 - 10^-13
Gamma rays: 10^-10 - <10^-16
How are EM waves classed?
EM waves are classed based on their origin, not frequencies or wavelengths
hence why gamma and x-rays overlap
e.g. x rays come from fast moving electrons
gamma rays come from unstable nuclei
Properties of EM waves
em waves are transverse, they can be plane polarised
they can be diffracted, reflected, refracted.
they don’t require a medium
they travel at the speed of light in a vacuum
how to use a ripple tank to observe wave effects
an oscillated paddle is connected to an electric motor in a tank
this will create transverse waves on the surface of the water
the depth can be adjusted to modelcrefraction
reflection can be observed against the edges of the tank
diffraction can be model by adding a slit into the tank
how can polarisation of light be demonstrated
using polaroid filter. Polaroid filters are made of long strips of crystals.
when the polaroid filters are placed on each other with the same orientation, the intensity is maximum.
As one is rotated to 90 degrees the intensity falls to a minimum because light falls to a
what are the two conditions for total internal reflection
the light must be travelling from a material with a higher refractive index to a material with a lower refractive index
the angle of incidence must be greater than or equal to the critical angle (Sin C = 1 / n )
