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wow woah insane its the best science flash cards in the observable universe confirmed > Waves > Flashcards

Waves Flashcards

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1
Q

Reflection

A

Wave changes direction at the boundary of a medium:

  • moves away from new medium
  • angle of incidence = angle of reflection
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2
Q

Refraction

A

Wave changes direction as it passes between mediums:

  • moves into new medium
  • wavelength and speed change
  • wave bends towards normal when slowing down
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3
Q

Find wave speed

A 
Speed = wavelength*frequency
(v = λf)
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4
Q

Polarised waves

A
  • oscillations in only one plane

- only transverse waves

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5
Q

Polarising filter

A
  • filters oscillations into one direction
  • unpolarised&raquo_space; polarised causes a brightness decrease
  • polarised&raquo_space; polarised effect depends on angle of the filters
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6
Q

Result of two parallel polarising filters

A

Same as a single filter

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7
Q

Result of two perpendicular polarising filters

A

Blocks most light

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8
Q

Intensity

A

Radiant power through a surface per unit area

P/A

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9
Q

Find intensity at distance r from a spherical wave source

A 
Intensity = power/spherical surface area
(I = P/4πr²)
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10
Q

Relationship between intensity and amplitude

A

Intensity is proportional to amplitude^2

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11
Q

Snell’s law

A

n1sin(i) = n2sin(r)

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12
Q

Find refractive index

A

Refractive index = speed in vacuum/speed in material

n = c/v

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13
Q

Where are angles measured from in reflection and refraction?

A

The normal to the boundary

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14
Q

Snell’s law for critical angle

A

n1*sin(i) = n2

because angle of refraction is 90 so sin(r) = 1

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15
Q

Total internal reflection

A

When angle of incidence is greater than the critical angle, so only reflection happens

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16
Q

Coherent waves

A

Waves with a constant phase difference at their sources

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17
Q

Wave superposition

A

Two waves overlap and resultant displacement = sum of individual displacements

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18
Q

How to form a stationary wave

A

Interference of two progressive waves with:

  • opposite directions
  • same speed
  • same frequency
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19
Q

Nodes of a stationary wave

A

Points with no amplitude (displacement always 0)

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20
Q

Antinodes of a stationary wave

A

Points with max amplitude

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21
Q

Find wavelength using a diffraction pattern

A

Wavelength = slit separation*fringe separation/distance from screen
(nλ = dsinθ
or
nλ = ax/D)

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22
Q

Find wave period

A 
Period = 1/frequency
(T = 1/f)
23
Q

Find frequency (using wavelength)

A 
Frequency = speed/wavelength
(f = v/λ)
24
Q

Find frequency (using period)

A 
Frequency = 1/period
(f = 1/T)
25
Q

Transverse wave

A

Wave where oscillations are perpendicular to wave direction

26
Q

Longitudinal wave

A

Wave where oscillations are parallel to wave direction

27
Q

When is diffraction through a gap strongest?

A

When gap width = wavelength

28
Q

Wavelength range of radio

A

> 0.1 m

29
Q

Wavelength range of microwaves

A

1 mm < λ < 0.1 m

30
Q

Wavelength range of infrared

A

700 nm < λ < 1 mm

31
Q

Wavelength range of light

A

400 nm < λ < 700 nm

32
Q

Wavelength range of ultraviolet

A

10 nm < λ < 400 nm

33
Q

Wavelength range of x-rays and gamma rays

A

< 10 nm

34
Q

Properties of EM radiation

A
  • can be reflected, refracted and diffracted
  • transverse (so can be polarised)
  • can travel through a vacuum (at 3 x10^8 m/s)
35
Q

1st order maxima

A

The set of points in an interference pattern where:

  • path difference = 1 λ
  • phase difference = 2π (same as 0)
  • there is constructive interference
  • resultant wave with max amplitude is formed
36
Q

1st order minima

A

The set of points in an interference pattern where:

  • path difference = 0.5 λ
  • phase difference = π
  • there is destructive interference
  • resultant wave with min amplitude is formed
37
Q

Phase difference

A

Difference in wave cycle progress between two points on a wave / waves (written as the diff in x value of two sin graphs)

38
Q

Path difference

A

Difference in the distances of two waves from their own sources (can be measured in regular distance or in wavelengths)

39
Q

Constructive interference

A

Superposition of two coherent waves in phase to form a resultant wave of maximum amplitude

40
Q

Destructive interference

A

Superposition of two coherent waves in antiphase to form a resultant wave of minimum (or 0) amplitude

41
Q

Amplitude

A

A wave’s maximum displacement from equilibrium

42
Q

Wave displacement

A

Distance of a point from equilibrium in a given direction

43
Q

Wavelength

A

Distance between adjacent peaks of a wave

44
Q

Wave period

A

Time taken for one wavelength to pass a point

or time taken for a full oscillation at one point

45
Q

Frequency

A

Number of wavelengths that pass a point per second

or number of full oscillations per second at one point

46
Q

Interference

A

Superposition of coherent waves

47
Q

Points in phase with each other in progressive vs standing waves

A

Progressive - points that are one wavelength apart are in phase
Standing - all points on the same side of equilibrium are in phase (same wave cycle progress)

48
Q

Energy transfer in progressive vs standing waves

A

Progressive - energy transferred in wave direction

Standing - no net energy transfer

49
Q

Amplitude in progressive vs standing waves

A

Progressive - all points have the same amplitude

Standing - amplitude changes along the wave (max at antinodes and 0 at nodes)

50
Q

Fundamental frequency of a taut string / open tube

A
  • frequency of the first standing wave that the string / tube can form (first harmonic)
  • both ends are nodes for a string
  • both ends are antinodes in a tube
  • wavelength is double the string / tube length
51
Q

Harmonics

A

Standing waves used to make sound in an instrument - frequency is a multiple of the fundamental frequency (odd multiples for closed tubes)

52
Q

Fundamental frequency of a closed tube

A
  • frequency of the first standing wave that the tube can form
  • open end must be an antinode
  • closed end must be a node
  • wavelength is 4x the tube length
53
Q

Wavelength in standing waves

A

Double the distance between two adjacent nodes

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