Combining Waves Flashcards

1
Q

What is a Stationary Wave

A

A wave which transfers no energy and whose positions of maximum and minimum amplitude are constant

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2
Q

How are stationary waves produced

A

A stationary wave is produced from the superposition fo 2 progressive waves travelling in opposite directions

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3
Q

What is Interference

A

The superposition of waves from two coherent sources of waves

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4
Q

What are the conditions for a stationary wave to be produced

A
  • The waves must be of the same frequency, wavelength and amplitude (cohernet)
  • They must be travelling in opposite directions
  • This normally happens when a wave is reflected back onto itself
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5
Q

What does Coherent mean

A

When two waves have a fixed phase difference and same frequency

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6
Q

What are the Different Types of Interference

A
  • Constructive interference - when 2 waves have displacement in the same direction
  • Destructive interference - when one wave has positive displacement and the other has negative displacement
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7
Q

Describe Destructive and Constructive Interference Diagram

A
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8
Q

What is Total Destructive Interference

A

If the waves have equal but opposite displacements so they cancel each other out

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9
Q

Describe Young’s Double Slit Experiment

A
  • Shine a coherent light source through 2 slits about the same size as the wavelength of the laser light so the light diffracts
  • Each slit acts as a coherent point source making a pattern of light and dark fringes
  • Light fringes are formed where the lights interfere constructively, this occurs where the path difference between waves is a whole number of wavelengths (nλ, where n is an integer)
  • Dark fringes are formed where the light interferes destructively, this occurs where the path difference is a whole number and a half wavelengths ((n+½)λ)
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10
Q

Describe Young’s Double Slit Experiment Diagram

A
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11
Q

Describe what happens using White Light rather than Monochromatic in Young’s Double Slit

A

Gives wider maxima with a central white fringe with alternating bright fringes (violet is closest to the central maximum and red furthest)

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12
Q

Explain what happens to the amplitude of two wave superposing when the frequency of them decreases

A
  • If the frequency decreases then their wavelengths will decrease
  • So the path difference will get closer and closer to one wavelength
  • Therefore the ampltiude will get bigger as the waves become more in phase
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13
Q

How would you increase the accurancy of finding the wavelength of Young’s Double Slit Experiment

A
  • Increase the distance from the screen to the slits - when the distance is greater the fringe spacing is greater so the maximas are easier to read off
  • Measure across 2 maximas and taking the mean - reduces percentage error
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14
Q

What is the FringeSpacing Equation

A

w = λD/s

Fringe Space (m) = Wavelength(m) x Distance from slits to screen(m) / Slit Spacing (m)

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15
Q

Describe the Safety Procuations of Using Lasers

A
  • Wear ​laser safety goggles
  • Don’t ​shine the laser at​ reflective surfaces
  • Never shine the laser at a person
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16
Q

Why do we use a lazer to show iterference and diffraction

A

Lazers produce monochromatic light so diffraction and interference patterns are more defined

17
Q

How was the knowledge and understanding of the nature of electromagnetic radiation changed over time

A
  • Young’s double slit experiment showed that light can diffract and have interference
  • These are wave properties so proved that​ electromagnetic radiation must act as a wave​ (at least some of the time).
  • At the time some theories suggested light was formed of tiny particles, however this experiment disproved that theory
18
Q

Describe the Different Orders Diagram

19
Q

What is a Node and an Antinode

A
  • Node - a point on a stationary wave where the displacement is 0
  • Antinode - a point on a stationary wave with maximum displacement
20
Q

What is a Harmonic

A

A mode of vibration that is the multiple of the first harmonic

21
Q

Describe Three Lowest Harmonics in a Diagram

22
Q

Describe the Three Lowest Harmonics of a Stationary Wave

A
  • First Harmonic- two nodes at either end and an antinode in the middle, wavelength is 2L
  • Second Harmonic - three nodes and two antinodes, wavelength is L
  • Third Harmonic - four nodes and three antinodes, wavelength is 2L/ 3
23
Q

What is the Fundamental Mode of a Stationary Wave

A

The Lowest Harmonic

24
Q

What is First Harmonic Equation

A

f = 1/2 x L x square root T/u

Frequency (Hz) = 1/ 2 x Length (m) x Tension (N) / Mass per unit length (kg m-1)

25
What is Path difference
The difference in the distance travelled by two waves
26
What is Diffraction
When waves spread around an obstacle or through a gap
27
When is there Maximum Diffraction
When the gap is the same as the wavelength
28
Describe the Single Slit Diffraction Graph
A ​bright central fringe​, which is double the width of all other fringes, with alternating dark and bright fringes on either side
29
Describe how can you vary the width of the central maximum
* Increasing​ the ​slit width​ - ​decreases the amount of diffraction ​so the central maximum becomes ​narrower ​and its intensity ​increases​ * Increasing​ the light ​wavelength​ - ​increases the amount diffraction​ as the slit is closer in size to the light’s wavelength, so the central maximum becomes ​wider​ and its intensity ​decreases
30
What is a Diffraction Grating
A slide containing many ​equally spaced slits
31
Why would you use a diffraction grating
The interference pattern is much sharper and brighter ​than it would be in Young's Double Slit Experiment this is because there are many more rays of light reinforcing the pattern
32
Describe the Single Slit Diffraction Graph with 50 slits compared to 20 slits
33
What is the Diffraction Grating Equation
d sin(𝛳) = n λ Distance between Slits(m) x Sin (angle between 0th and n order maxima) = Order of the Maxima x Wavelength (m)
34
Explain where the formual dsinθ = nλ is derived from
* For the first order maximum, the path difference between two adjacent rays of light is 1λ and the angle between the normal to the grating and the right ray is θ * A right angled triangle is formed, with side lengths d and λ, the upper angle is θ * For the first maxima sinθ = λ/d this rearranges to dsin = λ * For other maxima the path difference between the two rays of light is nλ, where n is the order of maxima
35
How would you calculate the distance between the slits using the number of lines per metre
You divide the number of lines per metre by 1 (for example if you know there are 300 lines per metre the distance between the slits would be 1/300 m)
36
What are the Applications of Diffraction Grating
* Line Absorption Spectra - splits up light from stars and is used to identify elements present in stars * X-ray Crystallography - crystal sheet acts as diffraction grating the X-ray passes through, used to find the spacing between atoms