Waves (M4) Flashcards
Fundamental frequency
The lowest frequency an object (eg a string) can vibrate at.
Harmonic
An integer multiple of the fundamental frequency
Stationary wave
Two progressive waves with the same frequency (and ideally the same amplitude) travelling in opposite directions are superposed. It remains in a constant position with no net energy transfer.
Characterised by nodes and antinodes.
Node
A point on a stationary wave where displacement is always zero, therefore amplitude and intensity are zero.
Antinode
A point on a stationary wave of greatest amplitude and therefore intensity.
Interference
Superposition of two progressive waves from coherent sources to produce a resultant wave with a displacement equal to the sum of the individual displacements from the two waves.
Constructive interference
Superposition of two waves in phase so that the resultant wave has greater amplitude than the original waves.
Destructive interference
Superposition of two waves in antiphase so that the waves cancel each other out and the resultant wave has a smaller amplitude than the original waves.
Phase difference
The difference between the displacements of particles along a wave, or two different waves.
Measured in degrees or radians, with each complete cycle, or a difference of one wavelength representing 360° or 2pi radians.
Path difference
The difference in the distance travelled by two waves from their source to a specific point.
Young’s double slit equation
L = ax/D
L = wavelength
a = separation between slits
x = separation between fringes
D = distance between the screen and the slits
a«D
Principle of superposition of waves
When two waves of similar types meet at a point, the resultant displacement at that point is equal to the sum of the displacements of the individual waves.
Coherent
Two wave sources, or waves, that have a constant phase difference and the same frequency.
Monochromatic
Light of a single frequency
Plane polarised
Description of a transverse wave in which the oscillations are limited to only one plane.
Partially polarised
Description of a transverse wave in which there are more oscillations in one particular plane, but the wave is not completely plane polarised.
Occurs when transverse waves reflect off a surface.
Unpolarised
Description of a transverse wave in which the oscillations occur in many planes.
Electromagnetic waves
Transverse waves with oscillating electric and magnetic components that do not need a medium to travel through.
They all travel at the speed of light through a vacuum.
EM wavelengths
Radio: >10^6 - 10^-1
Microwaves: 10^-1 - 10^-3
Infra red: 10^-3 - 7x10^-7
Visible light: 7x10^-7 - 4x10^-7
UV: 4x10^-7 - 10^-8
X-ray: 10^-8 - 10^-13
Gamma: 10^-10 - <10^-16
Refractive index
A measure of the bending of a light ray when passing through one medium into another.
Total internal reflection
When all the light is reflected back into the original medium. There is no light energy refracted out of the original medium.
Amplitude
Maximum displacement from the equilibrium position.
Symbol: A
Unit: m
Wavelength
Maximum distance between two points in phase on adjacent waves, for example one peak to the next or one compression to the next.
Symbol: lambda
Unit: m
Frequency
The number of wavelengths passing a given point per unit time.
Symbol: f
Unit: Hz
Period
The time taken for a wave to move one whole wavelength past a given point.
Symbol: T
Unit: s
Progressive wave
An oscillation that travels through matter (and in some cases through a vacuum). All progressive waves transfer energy but not matter.
Longitudinal wave
A wave where oscillations are parallel to the direction of energy transfer.
Transverse wave
A wave where the oscillations are perpendicular to the direction of energy transfer.