Chapter 6 Flashcards
What does the principle of superposition state?
That when 2 or more waves overlap (superpose), the resultant displacement at a given instant and position is equal to the sum of the individual displacements at that instant and position.
A wave transfers energy away from [ ]
It’s source
A progressive (moving) wave carries [ ] and usually information from one place to another without transferring any [ ]
Energy
Material
How can you tell that EM waves carry energy?
They heat things
How can you tell that X-rays and Gamma rays carry energy?
They knock electrons out of their orbits, causing ionisation
How can you tell that sound waves carry energy?
They cause things to vibrate
How can you tell that water waves carry energy?
Wave power can be used to generate electricity
Since waves carry energy, the source of the wave [ ]
Loses energy
Define Displacement (X, m)
How far a point on the wave has moved from its undisturbed position
Define Amplitude (a, m)
Maximum displacement
Define Wavelength (λ, m)
The length of one whole wave
Define Period (T, s)
The time taken for a whole vibration
Define Frequency (f, Hz)
The number of vibrations per second passing a given point
Define phase difference
The amount by which one wave lags behind another wave (degrees or radians)
What is intensity?
The rate of flow of energy per unit area perpendicular to the direction of travel of the wave
Equation for intensity
Intensity (I, Wm⁻²) = Power (P, W) / Area (A, M²)
When does superposition happen?
When 2 or more waves pass through each other
Superposition: What happens at the instant the waves cross?
The displacements from each wave combine
The principle of superposition:
When 2 or more waves cross, the resultant displacement = the vector sum of the individual displacements
Interference can be [ ] or [ ]
Constructive or Destructive
What is total destructive interference?
When a peak and a trough are of equal size and they completely cancel each other out
When is destructive interference not total?
When the waves are not the same size
What are the arrows called, that represent wave superposition?
Phasors
In [ ] means in step
Phase
2 points on a wave are in phase if they are both at the [ ] in the [ ].
same point
wave cycle
360° = ? Radians
2π Radians
Describe the waves that are in phase
Points that have a phase difference of 0 or a multiple of 360° are in phase. Their phasors point in the same direction.
Describe the waves that are in anti-phase
Points with a phase difference of odd-number multiples of 180°. Their phasors point in opposite directions.
To get interference patterns the 2 sources must be [
Coherent.
Define coherent
2 waves are coherent if they have the same wavelength and frequency and a fixed phase difference between them.
Define path difference:
The amount by which the path travelled by one wave is linger than the path travelled by the other wave
Describe the situation where you will get constructive interference from 2 waves
At any point an equal distance from both sources (coherant and in phas) or where the path difference os a whole number of wavelengths
Path difference = nλ
Describe the situation where you will get total destructive interference from 2 waves
At any point where the path difference is an odd number of half wavelengths
Path difference = (2n+1)λ / 2 = (n + 1/2) λ
What happens when a wave passes through a gap roughly the same width as its wavelength?
The waves spread out.
What does diffraction alter?
ONLY how far the wave spreads out.
What does the zeroth, first and second order represent?
The maximums produced at a path difference of zero, one and two wavelengths.
What equation can we use to determine the wavelength of light passing through two slits? What can we also use this for?
dsin θ = n λ. Diffraction gratings.
What difference does having a diffraction grating vs two slits make?
Brighter image, sharper fringe pattern and can also spread white light out into its component colours because each wavelength of light will produce a maximum at a different angle.
Line separation=
1/number of lines per metre
Snells Law-
n=sini/sinr=C1stmedium/C2ndMedium
