Chapter 12 Waves 2 Flashcards by Henry Triff

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.

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What is constructive interference?

This is when the displacement of the two meeting waves produces a higher displacement and so increases the amplitude

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What is destructive interference?

This is when the displacement of the two meeting waves produces a lower displacement so decrease the amplitude

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If the two waves have the same amplitude but the oposite displacements, what will happen?

The overall amplitude will be 0

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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.

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What is coherence?

This is when two waves from two sources have a constant phase difference

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What can be deduced from coherant waves?

The two waves have the same frequency

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What is a maxima?

This is the point of maximum constructive interference

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What is a minima?

This is the point of minimum constructive interferance

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What is a path difference?

This is the difference in the distances each wave from two different sources has travelled

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What is known about the path difference of a maxima?

The path difference is a whole number of wavelengths

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What is know about the path difference of a minima?

The path difference is half a wavelength. e.g. 1.5λ or 5.5λ

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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

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What are the units / measurements of phase difference?

Either wavelength or degrees or radians

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What is monochromatic light?

This is light that is all one frequency

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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