Chapter 12 Waves 2 Flashcards
What is the principle of superposition?
This is when two waves overlap, they superpose. When two waves meet at a point the resultant displacement at that point is equal to the sum of the displacements of the individual waves.
What is constructive interference?
This is when the displacement of the two meeting waves produces a higher displacement and so increases the amplitude
What is destructive interference?
This is when the displacement of the two meeting waves produces a lower displacement so decrease the amplitude
If the two waves have the same amplitude but the oposite displacements, what will happen?
The overall amplitude will be 0
What can be seen with ripples in a pond from two sources?
An interference pattern can be seen. Where the waves are in phase there is constructive interference and where waves are out of phase there is destructive interference.
What is coherence?
This is when two waves from two sources have a constant phase difference
What can be deduced from coherant waves?
The two waves have the same frequency
What is a maxima?
This is the point of maximum constructive interference
What is a minima?
This is the point of minimum constructive interferance
What is a path difference?
This is the difference in the distances each wave from two different sources has travelled
What is known about the path difference of a maxima?
The path difference is a whole number of wavelengths
What is know about the path difference of a minima?
The path difference is half a wavelength. e.g. 1.5λ or 5.5λ
What is the central maxima and what is known about it?
It is the middle maxima where the path difference between the waves is 0λ and is equidistance between the two sources
What are the units / measurements of phase difference?
Either wavelength or degrees or radians
What is monochromatic light?
This is light that is all one frequency
What is youngs two slit experiment?
This is when a single source of monochromatic light is shone diffracts through two slits that then cause an interference pattern on a screen
What did Youngs two slit experiment show?
It showed that light was a wave
What is the equation for youngs two slit experiment?
λ = ax / D λ = wavelength a = the slit separation x = the difference between maxima on the screen D = distance between the screen and the two slits
What is a stationary wave?
This is the product of two progressive waves that constructively interfere and appears to be stationary
What is a node and antinode?
A node is the point on a stationary wave where there is no displacement. An antinode is the point of maximum dispalcement
The separation between two nodes is…
equal to the wavelength
What is special about a stationary wave verses a progressive wave?
Stationary waves do not transfer energy
What can be said about the phase of particles along a stationary wave?
Between two nodes all the particles are in phase, they all reach there maxima at the same time but their amplitudes are different.
On different sides of a node, the particles are in antiphase
What is the fundamental frequency?
This is the minimum frequency for a stationary wave on a string
What is a harmonic?
This is the different frequencies that form a stationary wave on a string. They are related to the fundamental frequency
What is the wavelength, frequency and frequency as a multiple of f0 for the first 5 harmonics of a string with a fundamental frequency of 20Hz
1: 20Hz 2Lλ f0
2: 40Hz Lλ 2f0
3: 60Hz 1.5Lλ 3f0
4: 80Hz 0.5Lλ 4f0
5: 100Hz 2/5Lλ 5f0
Why do harmonics occur?
Because there has to be a node at either end and then the length of the string does not change so the amount that the string can be divided into is limited
How is a stationary wave formed with sound?
A speaker is faced against a solid surface. This causes a node to be formed where the solidsurface is
Why is there a node formed at the end of a tube that is closed at one end?
Because the air at the end cannot move because it is against a wall. So therefore it forms a node
What do we know about a stationary wave in a tube with a closed end?
There is a node at the closed and an antinode at the open end
What is the wavelength of the first harmonic of a stationary wave formed in a tube with a closed end
4x the length of the tube
What are the harmonics of a tube with a closed end?
They are all odd multiples of the fundamental frequency because that would require a antinode to form at the closed end which isn’t possible
What happens with stationary waves in an open tube?
An antinode forms at each end
All integer multiples of f0 can be made
