Waves Flashcards
What is a transverse wave
The oscillations are perpendicular to the direction of energy transfer. Particles vibrate. Have peaks and troughs. Example - Em waves
What is a longitudinal wave
Oscillations that are parallel to the direction of energy transfer. Particles vibrate.
What is a progressive wave
An oscillation that travels through a medium, transferring energy from one place to another but not matter.
What is phase difference
The difference in displacement between 2 waves given in degrees or radians, found by displacement/wavelength * 360 or 2pi
Using an oscilloscope to find wave frequency
The time base is the time period given by one square on the screen. f = 1/T
What is reflection and law of reflection
Reflection occurs when a wave changes direction at a boundary between 2 mediums, remaining in the same medium. Angle of incidence to normal is equal to angle of reflection to normal.
What is refraction
When a wave passes into another medium, the speed and direction at which it was previously traveling is altered. If the wave slows down, it refracts towards the normal. If it speeds up, it refracts away from the normal. Always partial reflection when wave is refracted.
What is diffraction
When a wave passes through a gap, it spreads out. If the gap is similar in size to the wavelength, there is a greater degree of defraction.
What is polarisation
When the particles are confined to vibrate in a single plane. Longitudinal waves cannot be polarised as they are already confined to a single plane. A polariser is used to polarise em waves.
What is intensity
The radiant power of a progressive wave passing through a surface per unit area. Intensity is directly proportional to amplitude^2
Wave length of radio waves
10^6 - 10^-1
Wavelenght of microwaves
10^-1 - 10^-3
Wavelength of infrared
10^-3 - 7*10^-7
Wavelength of visible light
700-400 nanometres, 10^-7
Wavelength of ultraviolet
4*10^-7 - 10^-8
Wavelength of xrays
10^-8 - 10^-13
Wavelength of gamma rays
10^-10 - 10^-16. Wavelengths of x rays and gamma rays may overlap.
What is a a refractive index
It is the factor to which the speed of a wave entering that medium will be altered by.
nsin§ = k
refraction index multiplied by sin(angle of INCIDENT wave to the normal) = a constant. Used to describe what happens when light changes medium.
Total internal relection
When light strikes the boundary to a medium with a lower refractive index than its current medium at an angle greater than the critical angle, all the light is reflected back into the original medium. The critical angle is found using the equation sinc = 1/n, where n is the refractive index of the medium being attempted to enter.
What is superposition
When 2 waves meet at a point, the displacement of both combine. If the waves are in phase, constructive interference occurs and the amplitude of the resultant wave is greater than both of the previous waves. If the waves are in anti phase, destructive interference occurs and the resultant displacement is smaller than both previous waves.
What is coherence
When 2 waves of the same frequency are emitted from 2 sources and have a constant phase difference. Minimas and maximas go up in half wavelengths, or pi.
What is the double slit experiment
A monochromatic source of light is emitted through 2 slits. The light diffracts as it passes through the slits and forms an interference pattern on an adjacent wall. Bright fringes indicate constructive interference, dark spots indicate destructive interference. The wavelength of the light can be found by multiplying the distance between the slits (a) by the distance between 2 adjacent spots, (x) and then dividing by the distance from the wall to the slits (d).
What is a stationary wave
When 2 progressive waves of same frequency travel in opposite direction and are superposed. Forms nodes where the waves are in antiphase and destructive interference occurs, and anti nodes where amplitude is max - constructive interference and the waves are in phase.
Harmonics
The first harmonic where the ends are fixed is half a wavelength. The first harmonic of an open tube is a half of a wavelength. The first harmonic of a tube open on one side is a quarter of a wavelength. All increase in increments of half wavelength per harmonic. Open tube, antinodes at each end. Fixed, nodes at each end. One side open, antinode at that end, node at the other.
