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Module 4 Interference Flashcards

(23 cards)

1
Q

Principal of superposition

A

when two waves of similar type meet at a point, the sum of their displacements is equal to the displacement of the resultant wave

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2
Q

What is a pulse?

A

A fragment of a wave

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3
Q

Define path difference

A

difference in the distance from one source to the detector compared to another source to the detector

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4
Q

Formula for path difference

A

S1P – S2P in meters (SP being length)

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5
Q

What is phase difference?

A

the angle by which a wave lags or leads another

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6
Q

What is the phase difference of waves in phase?

A

0 or 2π radians
(0 or 360 degrees)

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7
Q

What is the phase difference of two waves in anti-phase

A

π or 3π radians
(180 or 540 degrees)

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8
Q

Definition of coherent waves

A

when two waves of the same type are emitted with a constant phase difference, same frequency, wavelength, plane polarised in the same plane and similar amplitude (same magnitude)

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9
Q

Definition of interference

A

Superposition of two progressive waves from coherent sources to produce a resultant wave with displacement equal to the vector sum of individual displacement of the two waves

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10
Q

How is intensity increased if amplitude is doubled

A

intensity is increased by multiple of 4

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11
Q

What is constructive interference?

A

when two waves meet in phase their amplitude/displacement adds up

Path difference is a whole number of wavelengths

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12
Q

What is destructive interference?

A

When two waves meet exactly out of phase (in antiphase) the displacements cancel out and produce a wave of zero displacement and amplitude

Path difference is a whole number of wavelengths plus half wavelength

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13
Q

Explain how you would measure the wavelength of a monochromatic laser using two source interference?

A
  1. place the laser in front of a double slit board facing a screen
  2. measure the distance between the centre of the slits using a traveling microscope by using a vernier scale - this is a
  3. measure the distance between multiple fringes on the screen (say 8) then divide by the number of gaps (7) - this is x
  4. measure the distance between the double slit and screen - this is D
    use the formula λ = ax/D
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14
Q

How to observe the interference of sound waves?

A
  • Attach a speaker to a signal generator
  • place speaker behind a double slit board with slits approx 10cm wide
  • Measure distance between centre of slits on the board - this is a
  • Move a microphone parallel to the slit board at a given distance and measure where the maxima and minima are (loud and quiet) - this is x/2
    This is interference
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15
Q

YOUNGS DOUBLE SLIT EXPERIMENT WITH WHITE LIGHT

A

Central fringe is white (path difference is the zero for all wavelengths in white light)
Each constructive interference position is a spectrum from blue to red (blue is closest to the straight through position so at a smaller angle than red)

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16
Q

When investigating the interference of visible light, what is a suitable value for a (slit separation)?

17
Q

Why when carrying out Young’s double slit experiment, does the value for a (the slit) need to be approx = to the wavelength. of light being used?

A

so light diffracts so that interference can be observed

18
Q

When carrying out Young’s double slit experiment, why must multiple fringes be measured to find the value of x?

A

to reduce percentage error due to random error (unc on x)

you are measuring a larger distance for several fringes so error/measurement x 100 is lower ie percentage uncertainty lower

19
Q

Describe how you would observe two source interference using a microwave generator

A
  • Attach two transmitter cones to a microwave generator
  • Move a receiver probe parallel to the transmitter cones at a set distance
  • Receiver will measure alternating patterns of strong and weak signals
20
Q

How are fringes labelled?

A

as orders - zero order, first order, second order, etc. labelled from the straight through position
(order number is n in diffraction formula)

21
Q

What is a word to describe when waves are at 0º to each other?

22
Q

What do you use to measure the distance a in an the young’s double slit experiment?

A

a travelling microscope with a vernier scale

23
Q

What can be said about the relationship between wavelength and distance between maxima and minima?

A

shorter wavelength the shorter the path difference between maxima and minima

for maxima, path difference = whole wavelengths

for minima, path difference=half wavelength + whole wavelength