Define interference .

The combining of two or more waves to produce a resultant wave with a new amplitude.

Define the principle of superposition .

When two waves meet, they combine so that their displacements add together, then pass through and emerge unchanged on the other side.

What is the difference between constructive and destructive interference?

Constructive interference produces a resultant wave with a larger amplitude than the individual waves. Destructive interference produces a resultant wave with a smaller amplitude than the individual waves.

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

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

True or False? Two waves must have equal amplitude to be coherent.

False. Coherence requires only a constant phase difference and the same frequency — the amplitudes do not have to be equal.

Define monochromatic light.

Light consisting of waves of a single frequency .

Give one coherent and one incoherent light source.

Coherent: laser light Incoherent: a filament lamp

Define path difference .

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

Define phase difference .

The angle between the wave cycles of two points, describing how far apart they are in their cycle.

What path difference gives constructive interference?

A whole number of wavelengths, nλ , where n = 0, 1, 2, 3...

What path difference gives destructive interference?

An odd number of half wavelengths, (n + ½)λ , where n = 0, 1, 2, 3...

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

Path difference is generally expressed in multiples of wavelength .

What two conditions make two waves coherent ?

The same frequency and a constant phase difference .

True or False? Phase difference and path difference measure the same quantity.

False. Phase difference compares where two points are within their wave cycles. Path difference is the extra distance one wave has travelled compared with the other.

Define a stationary wave .

A wave produced by the superposition of two waves of the same frequency and amplitude travelling in opposite directions .

A point on a stationary wave where there is no vibration (zero amplitude).

A point on a stationary wave where the vibrations are at their maximum amplitude .

A stationary wave is usually produced by a travelling wave and its ..........

A stationary wave is usually produced by a travelling wave and its reflection .

Name three ways stationary waves can be demonstrated.

Stretched strings — an oscillator vibrating a string under tension Microwaves — a source aimed at a reflecting plate with a detector between Air columns — sound from a loudspeaker at the open end of a tube

True or False? The nodes and antinodes of a stationary wave move steadily along the string.

False. Nodes and antinodes are fixed in position along the string. Antinodes only move in the vertical direction; they do not travel along the wave.

What is the phase relationship between points lying between two adjacent nodes?

They are all in phase with one another.

Define mass per unit length ( μ ).

The mass of the string divided by its length , measured in kg m -1 .

The speed of a wave on a stretched string increases when the .......... is increased.

The speed of a wave on a stretched string increases when the tension is increased.

What is the dependent variable, and what may be used as the independent variable in Core Practical 7: Investigating Stationary Waves?

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

How is the first harmonic recognised on the string?

There is a node at each end and a single antinode in the middle .

After plotting frequency f against 1/ L , how is the wave speed found from the graph?

The wave speed equals 2 × the gradient of the line of best fit, since the gradient equals v /2.

What is the main source of random error in this experiment, and how can it be reduced?

Judging exactly when the first harmonic is reached (the sharpness of resonance ). Reduce it by adjusting the frequency while watching a node closely to find the largest response, and by taking repeat readings and averaging.

State two safety precautions for this experiment.

Use a rubber string (or wear goggles if using metal wire) in case it snaps Place a crash mat under the masses and stand clear in case they fall

True or False? The wave speed equals the gradient of the frequency against 1/ L graph.

False. The gradient equals v /2, so the wave speed is twice the gradient ( v = 2 × gradient).

A LevelPhysicsEdexcelFlashcards5. Waves & Particle Nature of LightInterference & Stationary Waves

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

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FrontInterference & Superposition of Waves
Define interference.

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Cards in this collection (34)

Define interference.
The combining of two or more waves to produce a resultant wave with a new amplitude.
Define the principle of superposition.
When two waves meet, they combine so that their displacements add together, then pass through and emerge unchanged on the other side.
What is the difference between constructive and destructive interference?
Constructive interference produces a resultant wave with a larger amplitude than the individual waves.
Destructive interference produces a resultant wave with a smaller amplitude than the individual waves.
Waves are coherent if they have a constant .......... and the same ..........
Waves are coherent if they have a constant phase difference and the same frequency.
True or False?
Two waves must have equal amplitude to be coherent.
False.
Coherence requires only a constant phase difference and the same frequency — the amplitudes do not have to be equal.
Define monochromatic light.
Light consisting of waves of a single frequency.
Give one coherent and one incoherent light source.
Coherent: laser light
Incoherent: a filament lamp
Define path difference.
The difference in distance travelled by two waves from their sources to the point where they meet.
Define phase difference.
The angle between the wave cycles of two points, describing how far apart they are in their cycle.
What path difference gives constructive interference?
A whole number of wavelengths, nλ, where n = 0, 1, 2, 3...
What path difference gives destructive interference?
An odd number of half wavelengths, (n + ½)λ, where n = 0, 1, 2, 3...
Path difference is generally expressed in multiples of ..........
Path difference is generally expressed in multiples of wavelength.
What two conditions make two waves coherent?
The same frequency and a constant phase difference.
True or False?
Phase difference and path difference measure the same quantity.
False.
Phase difference compares where two points are within their wave cycles. Path difference is the extra distance one wave has travelled compared with the other.
Define a stationary wave.
A wave produced by the superposition of two waves of the same frequency and amplitude travelling in opposite directions.
Define a node.
A point on a stationary wave where there is no vibration (zero amplitude).
Define an antinode.
A point on a stationary wave where the vibrations are at their maximum amplitude.
A stationary wave is usually produced by a travelling wave and its ..........
A stationary wave is usually produced by a travelling wave and its reflection.
Name three ways stationary waves can be demonstrated.
- Stretched strings — an oscillator vibrating a string under tension
- Microwaves — a source aimed at a reflecting plate with a detector between
- Air columns — sound from a loudspeaker at the open end of a tube
True or False?
The nodes and antinodes of a stationary wave move steadily along the string.
False.
Nodes and antinodes are fixed in position along the string. Antinodes only move in the vertical direction; they do not travel along the wave.
What is the phase relationship between points lying between two adjacent nodes?
They are all in phase with one another.
Give the equation for the speed of a wave on a stretched string.
$v = \sqrt{\frac{T}{μ}}$
where T = tension (N) and μ = mass per unit length (kg m^-1).
Define mass per unit length (μ).
The mass of the string divided by its length, measured in kg m^-1.
At the fundamental frequency, what is the wavelength on a string of length L?
$λ = 2 L$
Give the equation for the fundamental frequency of a stretched string.
$f_{0} = \frac{1}{2 L} \sqrt{\frac{T}{μ}}$
where L = length (m), T = tension (N) and μ = mass per unit length (kg m^-1).
The speed of a wave on a stretched string increases when the .......... is increased.
The speed of a wave on a stretched string increases when the tension is increased.
True or False?
Increasing the mass per unit length of a string increases the wave speed on it.
False.
Because $v = \sqrt{\frac{T}{μ}}$ , a larger mass per unit length μ gives a smaller wave speed.
What is the dependent variable, and what may be used as the independent variable in Core Practical 7: Investigating Stationary Waves?
Dependent variable: the frequency of the first harmonic
Independent variable: the length, the tension, or the mass per unit length of the string
How is the first harmonic recognised on the string?
There is a node at each end and a single antinode in the middle.
The tension in the string is calculated using the equation .........., where m is the added mass.
The tension in the string is calculated using the equation $T = m g$ , where m is the added mass.
After plotting frequency f against 1/L, how is the wave speed found from the graph?
The wave speed equals 2 × the gradient of the line of best fit, since the gradient equals v/2.
What is the main source of random error in this experiment, and how can it be reduced?
Judging exactly when the first harmonic is reached (the sharpness of resonance).
Reduce it by adjusting the frequency while watching a node closely to find the largest response, and by taking repeat readings and averaging.
State two safety precautions for this experiment.
- Use a rubber string (or wear goggles if using metal wire) in case it snaps
- Place a crash mat under the masses and stand clear in case they fall
True or False?
The wave speed equals the gradient of the frequency against 1/L graph.
False.
The gradient equals v/2, so the wave speed is twice the gradient (v = 2 × gradient).

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