Define interference .

Interference occurs when waves overlap and the resultant displacement is the sum of the displacements of each wave (based on the principle of superposition).

Define coherent waves.

Waves that have the same frequency and a constant phase difference .

What happens to the resultant wave when two coherent waves interfere constructively (in phase)?

The peaks and troughs of both waves line up, and the resultant wave has double the amplitude .

What happens to the resultant wave when two coherent waves interfere destructively (in antiphase)?

The peaks of one wave line up with the troughs of the other, and the resultant wave has no amplitude .

True or False? A filament lamp is a coherent light source.

False. A filament lamp produces non-coherent white light; a laser is an example of a coherent light source.

List four ways two-source interference can be demonstrated experimentally.

Water waves (ripple tank) Sound waves Light waves Microwaves

Define monochromatic light.

Light consisting of a single wavelength .

What two conditions must two light sources satisfy to produce an observable two-source interference pattern?

Coherent (constant phase difference) Monochromatic (single wavelength)

In a ripple tank, where do lines of maximum displacement occur?

Where the peaks and troughs of the two waves line up (peak meets peak or trough meets trough), corresponding to a path difference of a whole number of wavelengths.

Give a real-world application that relies on destructive interference of sound waves.

Noise-cancelling headphones — a compression from one wave lines up with a rarefaction from the other, so the waves cancel and no sound is heard.

True or False? A filament bulb can produce a two-source interference pattern in the same way as a laser.

False. A filament bulb is a non-coherent source of white light, so it cannot produce an observable interference pattern; only coherent, monochromatic sources (such as a laser) can.

A wave from source S 1 travels a distance of 4λ and a wave from source S 2 travels a distance of 6λ to reach point P. What type of interference occurs at P, and why?

Constructive interference occurs at P. The path difference is 6λ − 4λ = 2λ , which is a whole number of wavelengths.

Define fringe width , x , in Young's double-slit experiment.

The distance between successive bright fringes on the screen.

In a typical Young's double-slit set-up, the laser is placed behind a single slit before reaching the double slit. What is the effect of this single slit?

It diffracts the laser light, producing two light sources at slits A and B, which then diffract further to produce the interference pattern on the screen.

State three changes that each increase the fringe separation x in Young's double-slit experiment.

Increasing the wavelength λ of the light Increasing the distance D between the slits and the screen Decreasing the separation a between the slits

True or False? Increasing the distance between the screen and the double slits decreases the fringe separation.

False. Increasing the distance D between the slits and the screen increases the fringe separation x .

What two patterns are produced together in Young's double-slit experiment?

A diffraction pattern and an interference pattern made up of bright and dark fringes.

A LevelPhysicsCambridge (CIE)Flashcards8. SuperpositionInterference

Interference (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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Cards in this collection (23)

Define interference.
Interference occurs when waves overlap and the resultant displacement is the sum of the displacements of each wave (based on the principle of superposition).
Define coherent waves.
Waves that have the same frequency and a constant phase difference.
What is the condition for constructive interference between two coherent waves, in terms of path difference?
$path difference = n λ$
where n = 0, 1, 2, 3...
What is the condition for destructive interference between two coherent waves, in terms of path difference?
$path difference = (n + \frac{1}{2}) λ$
What happens to the resultant wave when two coherent waves interfere constructively (in phase)?
The peaks and troughs of both waves line up, and the resultant wave has double the amplitude.
What happens to the resultant wave when two coherent waves interfere destructively (in antiphase)?
The peaks of one wave line up with the troughs of the other, and the resultant wave has no amplitude.
True or False?
A filament lamp is a coherent light source.
False.
A filament lamp produces non-coherent white light; a laser is an example of a coherent light source.
Waves are coherent if they have the same frequency and a constant ...........
phase difference
List four ways two-source interference can be demonstrated experimentally.
- Water waves (ripple tank)
- Sound waves
- Light waves
- Microwaves
Define monochromatic light.
Light consisting of a single wavelength.
What two conditions must two light sources satisfy to produce an observable two-source interference pattern?
- Coherent (constant phase difference)
- Monochromatic (single wavelength)
In a ripple tank, where do lines of maximum displacement occur?
Where the peaks and troughs of the two waves line up (peak meets peak or trough meets trough), corresponding to a path difference of a whole number of wavelengths.
Give a real-world application that relies on destructive interference of sound waves.
Noise-cancelling headphones — a compression from one wave lines up with a rarefaction from the other, so the waves cancel and no sound is heard.
True or False?
A filament bulb can produce a two-source interference pattern in the same way as a laser.
False.
A filament bulb is a non-coherent source of white light, so it cannot produce an observable interference pattern; only coherent, monochromatic sources (such as a laser) can.
For destructive interference, the path difference must be a whole number of wavelengths plus a ...........
half wavelength
A wave from source S₁ travels a distance of 4λ and a wave from source S₂ travels a distance of 6λ to reach point P. What type of interference occurs at P, and why?
Constructive interference occurs at P.
The path difference is 6λ − 4λ = 2λ, which is a whole number of wavelengths.
Define fringe width, x, in Young's double-slit experiment.
The distance between successive bright fringes on the screen.
State the double-slit interference equation, defining each symbol.
$λ = \frac{a x}{D}$
- λ = wavelength of source (m)
- a = distance between the centres of the slits (m)
- x = fringe width (m)
- D = distance between the slits and the screen (m)
In a typical Young's double-slit set-up, the laser is placed behind a single slit before reaching the double slit. What is the effect of this single slit?
It diffracts the laser light, producing two light sources at slits A and B, which then diffract further to produce the interference pattern on the screen.
State three changes that each increase the fringe separation x in Young's double-slit experiment.
- Increasing the wavelength λ of the light
- Increasing the distance D between the slits and the screen
- Decreasing the separation a between the slits
In the double-slit equation, a represents the distance between the .......... of the two slits.
centres
True or False?
Increasing the distance between the screen and the double slits decreases the fringe separation.
False.
Increasing the distance D between the slits and the screen increases the fringe separation x.
What two patterns are produced together in Young's double-slit experiment?
A diffraction pattern and an interference pattern made up of bright and dark fringes.

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