Definitions 3 Flashcards
Progressive waves
Waves which transfer energy not matter as a result of oscillations or vibrations
Transverse waves
Waves where the oscillations of the particles in perpendicular to the direction of energy travel, resulting in crests and troughs
Longitudinal waves
Waves where the oscillations of the particles are parallel to the direction of energy travel
Frequency
The number of oscillations per unit time
Period
The time taken for one complete oscillation
Amplitude
The maximum distance of the particles in a wave, amplitude can never be negative
Displacement
The distance of a point on a wave from its rest or equilibrium position
Phase difference
The difference in the relative positions of two points on two waves of the same frequency
Intensity
The power per unit area or the energy passing through a unit area per unit time
Doppler effect
The change in observed frequency when a source moves relative to an observer
Electromagnetic waves
Transverse waves that can travel through a vacuum at the speed of light, they are formed from electric and magnetic fields oscillating at right angles
Polarisation
The restricting of the oscillations of the particles in a transverse wave to one direction at right angles to the direction of transfer of energy
Coherence
Two or more waves that have a constant phase difference and the same frequency, they do NOT need to have the same amplitude or wavelength
Principle of superposition
When two or more transverse or longitudinal waves travelling in opposite directions overlap to produce resultant displacements equal to the sum of the displacements on the original waves
Node
A position long a stationary wave with no vibration or zero amplitude
Antinode
A position along a stationary wave with maximum amplitude
Constructive interference
When two or more waves in phase produce a resultant wave with double the amplitude since the peaks and troughs of both waves line up, it is seen as bright fringes on a diffraction grating
Destructive interference
When two or more waves in anti-phase produce a wave with zero amplitude since the peaks on one of the waves lines up with the troughs of the other, it is seen as dark fringes on a diffraction grating
Stationary waves
Stationary waves are produced by the superposition of two waves of the same frequency and amplitude travelling in opposite directions
What are the properties of standing waves?
- The waves superposing must have the same frequency and amplitude
- They have nodes and antinodes
- All points between adjacent nodes vibrate in phase
- All points in adjacent loops oscillate in anti-phase
- The peaks and troughs of a standing wave do not move
Interference
Interference occurs whenever two or more waves superpose, it is the phenomenon when two coherent waves travel in opposite directions and overlap, leading to observable patterns of constructive and destructive interference
Diffraction
The spreading out of waves when they pass through or around an obstruction, any type of waves can be diffracted
Wavelength
The distance between points on successive oscillations of a wave that are in phase
What happens when the time-base on a CRO turns off?
A straight vertical line will show on the screen
Relationship between wavelength and frequency
Wavelength is inversely proportional frequency at a constant wave speed
What is intensity proportional to?
I ∝ amplitude^2 and frequency^2
What is intensity inversely proportional to?
I ∝ 1 / radius^2
The energy of a wave decreases rapidly with increasing distance
How is frequency related to energy in the EM wavespectrum?
The higher the frequency the more energy of radiation of the EM wave
λ of radio waves
> 1x10^-1 ms
λ of microwaves
10^-1 to 10^-3
λ of infrared waves
10^-3 to 7x10^-7
λ of visible light
7x^-7 to 4x10^-7
λ of UV
4x10^-7 to 10^-8
λ of X-rays
10^-8 to 10^-10
λ of gamma rays
10^-10 to 10^-16
Why can’t longitudinal waves be polarised?
Since the particles of longitudinal waves oscillate parallel to the direction of travel
What happens when unpolarised light falls on a polariser?
The intensity of unpolarised light will always fall by a half when it moves through a polariser
What if the polariser and analyser have the same orientation?
The transmission axes of polariser and analyser are 0° to each other, meaning the intensity of the light entering the analyser from the polariser will always equal toe intensity of the transmitted light leaving the analyser
What if the polariser and analyser are at right angles to each other?
The transmission axes are 90° to each other, meaning the intensity of light transmitted through the analyser will always be zero
The equation for polarisation
I transmitted = I incident * cos^2(θ)
θ = the angle between the polarisation direction of the incoming light and the transmission axis of the polariser
How do you calculate the length of a standing wave in a string?
L = nλ/2
n = 1,2,3…
How do you calculate the length of a standing wave in a tube open at one end?
L = nλ/4
n = 1,3,5… odd only
Why do standing waves in tubes with one end open have odd harmonics?
Since there is a node always formed at one end and an antinode at the open end, causing only odd multiples of 1/4λ to form
How do you calculate the length of a standing wave open at both ends?
L = nλ/2
n = 1,2,3…
What are the conditions for two source interference?
- The sources of the waves must be coherent monochromatic
- The slits must be narrow
What happens to a wave when it is diffracted?
The amplitude is decreases, but all other properties remain the same
Path difference
The difference in distance one wave has to travel compared to another to reach the same point
How do you calculate the path difference for constructive interference?
nλ
n = the order of the maxima
How do you calculate the path difference for deconstructive interference?
(n +1/2)λ
n = the order of the minima you want
To find the path difference find the difference between the two wavelengths
Double slit interference equation
λ = ax/D
a = distance between slits
x = successive bright fringe width
D = distance between slits to screen
Diffraction grating
A diffraction grating is a plate on which there is a very large number of parallel, identical, close-spaced slits; when coherent, monochromatic light is incident on a grating, a pattern of narrow bright fringes is produced on a screen
Diffraction grating equation
dsin(θ) = nλ
d = spacing between adjacent slits
θ = angle to the central maxima
n = order of maxima
How do you calculate the spacing between adjacent slits?
d = 1/N
N = lines per m,mm,cm…
How do you calculate the highest order of maxima visible?
n = d/λ
since sin(90) = θ = 1
if n is a decimal value, round down to nearest integer
How do you calculate the angle between maxima and central maxima?
θ = tan-1(h/D)
h = n * x (distance between successive maxima)
D = distance between slits to screen
What do bright fringes look like?
They appear as bright bands of lights; they are evenly spaced and their intensity decreases from either side of the central bright fringe
How do you find amplitude from CRO?
Amplitude = number of boxes that equal the amplitude * the time voltage setting
How do you find the period from a CRO?
Period = the number of boxes from one peak to another * time base setting
Time base setting
The time base refers to how many seconds each box is worth
Compressions and rarefactions on a displacement distance graph
Compressions and rarefactions always appear at x = 0 on the graph
How do you identify a compression?
Compression = if the displacements above and below the point at x = 0 are coming towards each other
How do you identify a rarefaction?
Rarefaction = if the displacements above and below the point at x = 0 are heading away from each other
What are the conditions for superposition?
- The waves must be the same type
- The waves must be coherent
- The amplitude does not necessarily need to be the same
What is diffraction affected by?
The extend to which diffraction depends on the width of the gap compared to the wavelength of the waves
- When the gap is smaller, there is more diffraction
- When the wavelength of larger, there is more diffraction
- Diffraction is the most prominent when the width of the gap is equal to the wavelength
Monochromatic light
Monochromatic light has a single-wavelength
What happens to the bright and dark fringes when the intensity of the light is reduced?
Both the bright and dark fringes will become darker
