Chapter 12: Waves 2 Flashcards
what is superposition?
when two waves overlap at a point in space
Principle of Superposition
“when two or more waves cross, the resultant displacement equals to the vector sum of the individual displacements”
Constructive Interference
if both waves are travelling in the same direction, the displacement combines into one big wave
Destructive Interference
when the waves are travelling in opposite directions and their displacements cancel out, waves are in antiphase
What does an increase in amplitude in constructive interference lead to?
increase in intensity
intensity is directly proportional to (amplitude)2
What is Interference
when two or more waves propagating in the same medium meet at a point
What do interference patterns consists of?
maxima and minima
How do you create a stable interference pattern?
use coherent waves
Coherence
waves emitted from two sources having a constant phase difference, must have the same frequency
What are maxima and minima both the results of?
result of two waves having travelled different distances from their source
path difference
difference in distance travelled by two waves from their sources to the point where they meet
What happens when the path difference is a whole number of wavelengths?
constructive interference
What happens when the path difference is a whole number AND A HALF of wavelengths?
destructive interference
(n + ½)λ
what is the central maxima?
a point where the path difference AND phase difference are both 0º
what is first order maxima?
path difference is one whole wavelength, phase difference is 360º, constructive interference occurs
what is first order minima?
path difference is half a wavelength. Phase difference of 180º, destructive interference occurs
phase difference
the difference in phase between two waves that arrive at the same point
measured in radians or degrees
what is needed to form an interference pattern?
two coherent waves
monochromatic light
single wavelength, single colour
what equipment is involved in Young’s double slit experiment
monochromatic light
narrow slit
What varies with the frequency of light used in Young’s Experiment
the distance between the maxima and the minima
what is the double slit equation
wavelength = distance between slits x width between maxima / distance from slit to the screen
when can you use the double slit equation?
when a < D
How are stationary waves produced?
superposition of two waves of the same frequency and amplitude travelling in opposite directions
what does a stationary wave look like?
peaks and troughs do not seem to move
how are stationary waves different to regular waves?
it stores energy instead of transferring it
Fundamental frequency
frequency of the fundamental mode of vibration
node
a region where there is no vibration
antinode
vibrations are at maximum amplitude
can nodes and antinodes move?
no
How do you calculate wavelength from nodes and atinodes?
The separation between adjacent nodes or antinodes = λ/2
How do you determine if two points are in or out of phase from their nodes/antinodes?
Points between nodes are in phase with each other
Points that have an odd number of nodes between them are out of phase
Points that have an even number of nodes between them are in phase
Experiment to investigate the superposition of sound
1) Use two speakers, a moderate distance apart, connected to the same signal generator to transmit sound waves
2) Walk along a line perpendicular to the speakers - you should hear alternating loud and quiet sounds
3) This is because in some places the wave from each speaker interfere constructively or destructively
What is Young’s double slit experiment
A single source of light directed towards a double slit, which creates two coherent beams of light, creates an interference pattern
True or False
Increasing the slit width increases the distance between two maxima
True
Harmonics
Points where the stationary wave form doesn’t change because the waves in each direction are reinforcing each other
