Define interference .

Interference occurs whenever two or more waves combine (by superposition) to produce a resultant wave with a new amplitude.

Define path difference .

Path difference is the difference in distance travelled by two waves from their sources to the point where they meet.

Define stationary wave .

A stationary wave (standing wave) is produced by the superposition of two waves of the same frequency and amplitude travelling in opposite directions , producing a wave pattern where the peaks and troughs do not move.

Define coherent (waves).

Waves are coherent if they have the same frequency and a constant phase difference .

Define phase difference .

Phase difference is the angle between the wave cycles of two points on a wave, or on different waves, that measures how far apart they are in their cycle.

What is the difference between a node and an antinode ?

Node : a point of no vibration Antinode : a point where the vibrations are at their maximum amplitude

What is the difference between constructive and destructive interference?

Constructive interference : the resultant wave has a larger amplitude than any of the individual waves Destructive interference : the resultant wave has a smaller amplitude than the individual waves

What path difference gives constructive interference, and what path difference gives destructive interference?

Constructive interference : path difference = n*λ * Destructive interference : path difference = (n + ½)*λ * where n is an integer (0, 1, 2, 3...)

How is a stationary wave usually produced in practice?

By a travelling wave and its reflection (e.g. off a fixed end, a reflecting plate, or the closed end of a tube) superposing.

What happens when two wavefronts travelling towards each other meet?

They combine by superposition , then pass through each other and emerge unchanged on the other side.

Two waves travel 6λ and 6.5λ respectively to reach point P. What type of interference occurs at P, and why?

Destructive interference. The path difference is 6.5λ – 6λ = λ/2, which is an odd number of half wavelengths, i.e. (n + ½)λ.

What is the phase relationship between points along a stationary wave that lie between two adjacent nodes?

All points between two adjacent nodes are in phase with each other.

What is meant by monochromatic light, and why does this matter for coherence?

Monochromatic light consists of light waves of a single frequency . Since coherent waves must have the same frequency, a coherent light source (e.g. a laser) must be monochromatic.

Path difference is generally expressed in multiples of .......... .

Path difference is generally expressed in multiples of wavelength .

In a stationary wave, nodes are .......... , while antinodes only move in the vertical direction.

In a stationary wave, nodes are fixed , while antinodes only move in the vertical direction.

A .......... lamp produces incoherent light waves, whereas a laser produces coherent light.

A filament lamp produces incoherent light waves, whereas a laser produces coherent light.

True or False? Phase difference and path difference mean the same thing.

False. Phase difference compares how far apart two waves are in their cycle (peaks and troughs). Path difference compares how much further one wave has travelled along its path than the other. They are related but distinct concepts.

True or False? The nodes of a stationary wave move back and forth along the string as the wave oscillates.

False. Nodes are fixed points of no disturbance and do not move. Only the antinodes move, and only vertically (in amplitude), not along the string.

True or False? Two waves are coherent as long as they have a constant phase difference, regardless of their frequencies.

False. Coherent waves must have both the same frequency and a constant phase difference — matching phase difference alone is not enough.

Define mass per unit length , μ .

Mass per unit length is the mass of the string divided by the length of the string: μ = mass ÷ length, in kg m -1 .

At the fundamental frequency of a stretched string of length L , what is the wavelength of the stationary wave, and why?

λ = 2 L , because at the fundamental (first harmonic) there is exactly half a wavelength between the two fixed ends of the string.

Increasing the .......... in a stretched string increases the speed of the wave travelling along it, since v = √( T / μ ).

Increasing the tension in a stretched string increases the speed of the wave travelling along it, since v = √( T / μ ).

True or False? A thicker, heavier string (larger mass per unit length) under the same tension will vibrate at a higher fundamental frequency than a thinner string.

False. Since f 0 = (1/2 L )√( T / μ ), a larger μ gives a lower fundamental frequency, not a higher one — this is why bass strings on a guitar are thicker.

In Core Practical 5, what is the independent variable and what is the dependent variable ?

Independent variable : either the length of the string, the tension in the string, or the mass per unit length Dependent variable : frequency of the first harmonic

How is the first harmonic identified when carrying out this experiment?

Increase the frequency of the vibration generator until nodes are seen at both ends of the string and a single antinode is observed in the middle.

How can the sharpness-of-resonance problem in judging the first harmonic be resolved?

Adjust the frequency while looking closely at a node , rather than the amplitude, since looking at amplitude is unreliable as the wave moves very fast.

If frequency, f , is plotted against 1/ L , what quantity can be found from the graph and how?

The wave speed , v . The gradient of the graph is v /2, so v is found by doubling the gradient.

Name two safety precautions to take when carrying out Core Practical 5.

Any two from: Use a rubber string instead of a metal wire, in case it snaps under tension If using a metal wire, wear goggles Stand well away from the hanging masses in case they fall Place a crash mat or soft surface under the masses to break their fall

The tension in the string is calculated using T = .......... , where m is the mass attached and g is the gravitational field strength.

The tension in the string is calculated using T = mg , where m is the mass attached and g is the gravitational field strength.

True or False? To improve the resolution of results in this experiment, measurements should be taken over as small a range of lengths as possible.

False. Measurements should span a suitable, large range (e.g. 20 cm intervals over at least 1.0 m) to give greater resolution, not a small range.

International A Level (IAL)PhysicsEdexcelFlashcards2. Waves & ElectricityInterference & Stationary Waves

Interference & Stationary Waves (Edexcel International A Level (IAL) Physics): Flashcards

Exam code: YPH11

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FrontInterference & Superposition of Waves
Define interference.

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Cards in this collection (32)

Define interference.
Interference occurs whenever two or more waves combine (by superposition) to produce a resultant wave with a new amplitude.
Define path difference.
Path difference is the difference in distance travelled by two waves from their sources to the point where they meet.
Define stationary wave.
A stationary wave (standing wave) is produced by the superposition of two waves of the same frequency and amplitude travelling in opposite directions, producing a wave pattern where the peaks and troughs do not move.
Define coherent (waves).
Waves are coherent if they have the same frequency and a constant phase difference.
Define phase difference.
Phase difference is the angle between the wave cycles of two points on a wave, or on different waves, that measures how far apart they are in their cycle.
What is the difference between a node and an antinode?
- Node: a point of no vibration
- Antinode: a point where the vibrations are at their maximum amplitude
What is the difference between constructive and destructive interference?
- Constructive interference: the resultant wave has a larger amplitude than any of the individual waves
- Destructive interference: the resultant wave has a smaller amplitude than the individual waves
What path difference gives constructive interference, and what path difference gives destructive interference?
- Constructive interference: path difference = n*λ*
- Destructive interference: path difference = (n + ½)*λ*
where n is an integer (0, 1, 2, 3...)
How is a stationary wave usually produced in practice?
By a travelling wave and its reflection (e.g. off a fixed end, a reflecting plate, or the closed end of a tube) superposing.
What happens when two wavefronts travelling towards each other meet?
They combine by superposition, then pass through each other and emerge unchanged on the other side.
Two waves travel 6λ and 6.5λ respectively to reach point P. What type of interference occurs at P, and why?
Destructive interference. The path difference is 6.5λ – 6λ = λ/2, which is an odd number of half wavelengths, i.e. (n + ½)λ.
What is the phase relationship between points along a stationary wave that lie between two adjacent nodes?
All points between two adjacent nodes are in phase with each other.
What is meant by monochromatic light, and why does this matter for coherence?
Monochromatic light consists of light waves of a single frequency. Since coherent waves must have the same frequency, a coherent light source (e.g. a laser) must be monochromatic.
Path difference is generally expressed in multiples of ...........
Path difference is generally expressed in multiples of wavelength.
In a stationary wave, nodes are .........., while antinodes only move in the vertical direction.
In a stationary wave, nodes are fixed, while antinodes only move in the vertical direction.
A .......... lamp produces incoherent light waves, whereas a laser produces coherent light.
A filament lamp produces incoherent light waves, whereas a laser produces coherent light.
True or False?
Phase difference and path difference mean the same thing.
False.
Phase difference compares how far apart two waves are in their cycle (peaks and troughs). Path difference compares how much further one wave has travelled along its path than the other. They are related but distinct concepts.
True or False?
The nodes of a stationary wave move back and forth along the string as the wave oscillates.
False.
Nodes are fixed points of no disturbance and do not move. Only the antinodes move, and only vertically (in amplitude), not along the string.
True or False?
Two waves are coherent as long as they have a constant phase difference, regardless of their frequencies.
False.
Coherent waves must have both the same frequency and a constant phase difference — matching phase difference alone is not enough.
State the equation for the speed of a wave travelling along a string with two fixed ends.
$v = \sqrt{\frac{T}{μ}}$
where T = tension in the string (N) and μ = mass per unit length of the string (kg m^-1)
Define mass per unit length, μ.
Mass per unit length is the mass of the string divided by the length of the string: μ = mass ÷ length, in kg m^-1.
State the equation for the fundamental frequency (first harmonic), f₀, of a stretched string of length L.
$f_{0} = \frac{1}{2 L} \sqrt{\frac{T}{μ}}$
where L = length of the string (m), T = tension (N), μ = mass per unit length (kg m^-1)
At the fundamental frequency of a stretched string of length L, what is the wavelength of the stationary wave, and why?
λ = 2L, because at the fundamental (first harmonic) there is exactly half a wavelength between the two fixed ends of the string.
Increasing the .......... in a stretched string increases the speed of the wave travelling along it, since v = √(T/μ).
Increasing the tension in a stretched string increases the speed of the wave travelling along it, since v = √(T/μ).
True or False?
A thicker, heavier string (larger mass per unit length) under the same tension will vibrate at a higher fundamental frequency than a thinner string.
False.
Since f₀ = (1/2L)√(T/μ), a larger μ gives a lower fundamental frequency, not a higher one — this is why bass strings on a guitar are thicker.
In Core Practical 5, what is the independent variable and what is the dependent variable?
- Independent variable: either the length of the string, the tension in the string, or the mass per unit length
- Dependent variable: frequency of the first harmonic
How is the first harmonic identified when carrying out this experiment?
Increase the frequency of the vibration generator until nodes are seen at both ends of the string and a single antinode is observed in the middle.
How can the sharpness-of-resonance problem in judging the first harmonic be resolved?
Adjust the frequency while looking closely at a node, rather than the amplitude, since looking at amplitude is unreliable as the wave moves very fast.
If frequency, f, is plotted against 1/L, what quantity can be found from the graph and how?
The wave speed, v. The gradient of the graph is v/2, so v is found by doubling the gradient.
Name two safety precautions to take when carrying out Core Practical 5.
Any two from:
- Use a rubber string instead of a metal wire, in case it snaps under tension
- If using a metal wire, wear goggles
- Stand well away from the hanging masses in case they fall
- Place a crash mat or soft surface under the masses to break their fall
The tension in the string is calculated using T = .........., where m is the mass attached and g is the gravitational field strength.
The tension in the string is calculated using T = mg, where m is the mass attached and g is the gravitational field strength.
True or False?
To improve the resolution of results in this experiment, measurements should be taken over as small a range of lengths as possible.
False.
Measurements should span a suitable, large range (e.g. 20 cm intervals over at least 1.0 m) to give greater resolution, not a small range.

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