Waves Flashcards
displacement (X) (oscillations)
instantaneous distance from the equilibrium position in a specific direction (m)
amplitude (Xo) (oscillations)
maximum displacement from the equilibrium position (m)
frequency (f) (oscillations)
number of oscillations per second (Hz)
period (T) (oscillations)
time for one oscillation (s)
phase (oscillations)
measure of how “in step” different particles are (one cycle = 360 degrees or 2 pi radians)
Definition of Simple Harmonic Motion (SHM)
SHM is a type of oscillation that takes place when the acceleration of (and force on) an object is:
- proportional to its displacement from the equilibrium position
- in the opposite direction to the displacement (i.e. towards equilibrium position)
Longitudinal Waves
the particles in the medium vibrate parallel to the direction of the energy transfer
Transverse Waves
the particles of the medium vibrate at right angles to the direction of energy transfer
Displacement (waves)
distance the medium has moved from the equilibrium position in a particular direction (m)
Frequency (f) (waves)
number of oscillations of the medium (or complete waves passing a point) per second (Hz)
Period (T) (waves)
time for one complete oscillation of the medium (or time for one complete wave to pass a given point) (s)
Wavelength
shortest distance between two points that are in phase along a wave, e.g. crest to crest (m)
Wave Speed
distance travelled per unit time by the energy of the wave (or by wavefront) (m/s)
Amplitude (A) (waves)
maximum displacement of the medium from the equilibrium position (m)
Intensity Definition
power per unit area received by an observer
Mechanical Wave
requires a medium to travel through
Electromagnetic Waves
do not require a medium to travel through
all EM waves are transverse
travel at 3 X 10^8 m/s in a vacuum/air
Relative Wavelengths of EM Waves
radio waves: 10^2 m microwaves: 10^-3 m infrared: 10^-5 m visible light: 10^-7 m ultra violet: 10^-9 m x rays: 10^-12 gamma rays: 10^-14
Conditions for Total Internal Reflection
- light is travelling from a more to a less optically dense medium
- the angle of incidence is greater than the critical angle
Diffraction
when the waves move past an obstacle or through a gap the waves tend to spread out, this spreading out is called diffraction
Principle of Superposition
“if two or more waves meet, the resultant displacement at any point is found by adding the displacements produced by each individual wave”
Anti nodal lines (interference)
- waves meet in phase
- constructive interference
- path difference = n x wavelength
- maximum amplitude
- “maxima”
- bright light or loud sound
Nodal lines (interference)
- waves meet out of phase
- destructive interference
- path difference = (n+1/2) x wavelength
- zero amplitude
- “minima”
- dark light or quiet sound
Conditions for Standing Waves to Form
waves must be:
- of the same amplitude
- of the same frequency
- travelling in opposite directions
Summary of Standing Waves
- strings and pipes have a range of resonant frequencies (harmonics) at which they will form standing waves
- strings and open pipes can produce all harmonics
- closed pipes can only produce odd-numbered harmonics
Polarisation Definition
if an EM wave such as light is polarised, the electric field vector is oscillating in one plane only
Brewster’s Law
when light reflects off a surface it will be polarised in the plane of the surface
the angle between the reflected and refracted ray has to be 90 degrees for polarisation to be 100%
Malus’ Law
polarising filter restricts the electric field vector of EM waves passing through it to a direction perpendicular to the embedded crystal chains
an analyser is a device that can detect polarised light, if the angle between the polarisation of the incident light is 0-90 then some light will pass through. If it = 90 then no light passes through.
if unpolarised light passes through a polariser, the light intensity will be reduced by half
Interference and Polarisation
two waves must have the same plane of polarisation in order to produce an interference pattern
waves of different polarisation cannot cancel or add they just create a wave of a different plane of polarisation
