4.4 - Waves Flashcards
What is a progressive wave
A wave which transfers energy from one point to another with a wave front that travels through the material
What is a longitudinal wave
A wave which oscillates in the same direction as the energy (rarefactions and compressions)
What is a transverse wave
A wave where the particles oscillate perpendicular to the energy (like EMF waves)
What is frequency measured in
Hertz (Hz)
What is wavelength
The distance between 2 adjacent points (e.g. peaks)
How to find time period of a wave using frequency
T = 1 / f
What is phase difference
The amount one wave lags behind another as proportion of the wavelength (measured in radians or degrees)
What do the axis on an oscilloscope measure
Vertical = Voltage / Amplitude
Horizontal = Time
What is refraction
It is when a wave bends at a boundary between 2 materials due to the change in density causing it to speed up or slow down
What is the difference between a polarised and unpolarised wave
Polarised waves contains waves oscillating along one axis. Unpolarised waves can be oscillating in any direction perpendicular to the axis of propagation
How is intensity defined in terms of power
Intensity is power / area
How fast do Electromagnetic waves travel in a vacuum
3x10^8 ms^-1 (speed of light)
What is refractive index
The refractive index is a measure of how fast light travels in a material compared to its speed in a vacuum
How to find refractive index of a material
n = c / v
n = refractive index
c = speed of light
v = velocity when in the material
What is the name of the angle of incidence at which the light will reflect off a boundary rather than refracting in the medium
The critical angle
How do you find the critical angle
SinC = 1 / n
C = critical angle
n = refractive index of material being passed into
What is total internal reflection
What happens to light at angles greater than the critical angle
What does it mean what a wave superposes
2 waves in the same place will combine to make a larger wave
What is constructive interference
The waves superpose and produce a singular wave and the displacement of the wave is equal to the sum of the displacements (troughs and peaks go further in their respective directions)
What is destructive interference
2 waves meet but the individual displacements are in opposite directions and counteract each other (Which could cause the wave to become a line)
What experiment is used to investigate the principle of superposition using sound
2 speakers that emit the same signal are a moderate distance away from each other. Then walk along a line perpendicular to the speakers (along the wall opposite the speakers and should hear difference between loud and quiet points). This is because some points the waves interfere constructively and other points destructively.
Will 2 waves in phase interfere constructively or destructively
Constructively
What is path difference
It is the difference in distance that 2 waves have travelled in terms of wavelength (units of length)
What is phase difference
The difference in the point in the cycle of 2 waves as a proportion of a full wave cycle (units of degrees/radians)
Why is a laser used in showing intereference and diffraction
It produced monochromatic light (same wavelength/colour)
What is Young’s double-split experiment
A single source of light directed towards a double slit which creates 2 beams of light this interferes as it hits the screen and creates an interference pattern (dots being brighter and dimmer)
What happens when you increase the slit width
It also increases the width of the central diffraction maximum
What is the equation that relates the wavelength of light to the slit spacing and distance to the screen
λ = a x / D
λ = wavelength
a = slit spacing
x = fringe spacing (on screen)
D = distance to screen
What are the 2 properties of light as a wave
Diffraction and Interference
How to find number of fringes which would be produced by a diffraction grating
n λ = D sinθ
What is the formula for total internal reflection
SinC = 1 / n
What formula is used to determine the angle of refraction in to a new medium
n1sinθ1 = n2sinθ2
n1 = refractive index of previous material
θ1 = angle it enters the material from
n2 = new mediums refractive index
θ2 = angle of refraction in the new material
What is a stationary wave
They are waves that consist of alternating fixed pattern of nodes and antinodes. No energy is transferred across the wave just up and down
What is a node
A point with no vibrations (amplitude is 0)
What is an antinode
A point with maximum vibration in which the resultant amplitude is at maximum
What are the conditions for a stationary wave to be produced
The waves must be coherent
The waves must be travelling in opposite direction. These conditions are met when a wave has reflected back onto itself
Give an example of an experiment you could do to show a stationary wave
An oscillator is used to pass a wave along a sting which is fixed at one end and the wave will form when the progressive wave is reflected off the fixed end (Diff frequencies create different harmonics)
What is a difference between a stationary and progressive wave
Stationary waves don’t transmit energy from one place to another
How to find speed of sound using resonance tube
Create a closed end pipe, using tuning fork hold above tube, move tube up until you find position which causes resonance, length will be a quarter of the wavelength, use speed = frequency x wavelength
What is a harmonic
A harmonic is a point where the stationary wave form doesn’t change because the waves in each direction are reinforcing each other
A string is oscillating at its fundamental frequency (1st harmonic) how many nods and antinodes are visible
Nodes - 2 (one at either end)
Antinode - 1 (in the middle)
() this shape but sideways
