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Physics Paper 1 > Combining Waves > Flashcards

Combining Waves Flashcards

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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

A
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

A
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
Q

What is Path difference

A

The difference in the distance travelled by two waves

26
Q

What is Diffraction

A

When waves spread around an obstacle or through a gap

27
Q

When is there Maximum Diffraction

A

When the gap is the same as the wavelength

28
Q

Describe the Single Slit Diffraction Graph

A

A ​bright central fringe​, which is double the width of all other fringes, with alternating dark and bright fringes on either side

29
Q

Describe how can you vary the width of the central maximum

A
  • 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
Q

What is a Diffraction Grating

A

A slide containing many ​equally spaced slits

31
Q

Why would you use a diffraction grating

A

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
Q

Describe the Single Slit Diffraction Graph with 50 slits compared to 20 slits

A
33
Q

What is the Diffraction Grating Equation

A

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
Q

Explain where the formual dsinθ = nλ is derived from

A
  • 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
Q

How would you calculate the distance between the slits using the number of lines per metre

A

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
Q

What are the Applications of Diffraction Grating

A
  • 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

Physics Paper 1 (15 decks)

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