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Physics (AS) > Chapter 4.4 - Waves > Flashcards

Chapter 4.4 - Waves Flashcards

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1
Q

Progressive wave

A

A wave in which the peaks and troughs move through the medium as energy is transferred.
Sound Waves, P-Waves

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2
Q

Displacement

A

Distance of a point from its rest position

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3
Q

Amplitude

A

Maximum magnitude of the displacement

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4
Q

Wavelength

A

The length of one full wave cycle

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5
Q

Period

A

Time taken for a whole cycle to complete

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6
Q

Frequency

A

Number of full cycles passing a point per second

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7
Q

Phase

A

A measurement of position of a certain point along a wave cycle

180deg = 1/2wavelength
360deg = 1 wavelength

Think of a circle i.e 180 degrees = half circle = half wavelength

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8
Q

Phase difference

A

Difference in phase between two points

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9
Q

Equation for wave speed

A

v=fλ

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10
Q

How an oscilloscope works

A

y axis is voltage, x axis is time and it plots a wave

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11
Q

Transverse waves

A

A wave in which the medium is displaced perpendicular to the direction of energy transfer - the oscillations of medium particles are perpendicular to the direction of travel.

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12
Q

Longitudinal waves

A

A wave in which the medium is displaced in the same line as the direction of energy transfer - oscillations of the medium particles are parallel to the direction of wave travel.

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13
Q

Intensity in terms of waves

A

The rate of flow of energy per unit area at right angles to the direction of travel

Intensity = Power / Area

4pir^2

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14
Q

How intensity is related to amplitude

A

Intensity is proportional to amplitude squared

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15
Q

Polarisation

A

To restrict vibrations of a transverse wave to a single direction

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16
Q

How visible light can be polarised

A

Using a polarising filter

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17
Q

How microwaves can be polarised

A

Using a metal grille. When the plane of oscillation is parallel to that of the grille, all the of energy will be absorbed and no polarised light will pass through, although some will be emitted in random directions. Most of the light makes it through when the plane is perpendicular (seems counter intuitive)

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18
Q

Diffraction

A

When waves spread out when they go through a gap

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19
Q

When will maximum diffraction occur

A

When the gap width is equal to the wavelength

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20
Q

How a ripple tank works and can be used to view wave effects

A

Ripple tanks are shallow tanks of water, where an oscillating paddle generates horizontal waves. Objects can be placed in the tank to create barriers

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21
Q

How intensity of a polarised wave is related to angle

A

cos^2 of the angle

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22
Q

Main principle of reflection of waves

A

angle of incidence = angle of reflection (where they are measured from the normal)

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23
Q

What happens when light is shone through a single slit

A

You get a diffraction pattern

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24
Q

Refraction

A

The change in direction of a wave when it enters a different medium

25
Q

Does a wave entering a denser medium bend towards or away from the normal

A

Towards the normal

26
Q

Refractive index of a material

A

The ratio between c and the speed of light in that material

n = c / v

27
Q

How to work out the new angle when light is refracted

A

n1sinθ1 = n2sinθ2

1 is a material and 2 is the other material

28
Q

How to investigate refraction

A

Use a raybox to shine a beam of light through a glass block and look at the light

29
Q

When total internal reflection occurs

A

when θ2 is equal to 90

therefore sin C = n2/n1 (n2 is usually air and is therefore 1)

30
Q

Total internal reflection

A

When light would enter a less dense medium but instead refracts so much that it is instead reflected off the inner surface

31
Q

How to investigate total internal reflection

A

Use a lightbox to shine a beam at light into a semi-circular glass block (shine it so it would hit the centre of where the full circle would be). Vary the angle of incidence. (The light should not be refracted when entering or leaving the block which allows you to just observe the total internal reflection)

32
Q

Principle of superposition of waves

A

When multiple waves cross, the resultant displacement equals the vector sum of the individual displacements

33
Q

How in-phase waves interfere

A

Constructively

34
Q

How waves that are nπ out of phase interfere

A

constructive if n is even

destructive if n is odd

35
Q

Coherent

A

Same wavelength, frequency and a fixed phase difference

36
Q

Path difference

A

The distance that one wave has moved further than another one

37
Q

How to observe interference with sound waves

A

Connect two speakers to the same oscillator and place them in line. Walk across the room parallel to them and there will be spots of loud and quiet

38
Q

Monochromatic

A

Only one wavelength present

39
Q

Young’s double slit experiment

A 
A coherent, monochromatic light is shone through two small slits onto a screen.  The light then interferes and creates light and dark minima and maxima on the screen.  Wavelength is calculated by λ = ax/D where
λ is wavelength
a is slit seperation
x is the spacing between adjacent maxima
D is the distance to the screen
40
Q

How to investigate interference of microwaves

A

Two microwave transmitter cones are connected to the same signal generator. A microwave receiver probe can then be moved along perpendicular to the direction of the waves and it should see alternating patterns of strong and weak signals

41
Q

Requirement of sizes for youngs double slit experiment

A

a &laquo_space;D

42
Q

What is a diffraction grating

A

Basically loads of slits

43
Q

Advantage of a diffraction grating over using two slits

A

The maxima are brighter and narrower and therefore easier to measure

44
Q

How to calculate wavelength of light from a diffraction grating

A 
nλ = dsinθ
where
λ is wavelength
n is the order
d is the slit seperation
θ is the angle of incidence
45
Q

What pattern is produced when white light is shone through a diffraction grating

A

The central maxima is white, but all they other maxima are spectra of visible light

46
Q

Stationary wave

A

The superposition of two progressive waves with the same wavelength, moving in opposite directions

47
Q

How to create a standing wave in a string

A

Fix one end and attach the other to an oscillator

48
Q

Node

A

Point on a standing wave where there is no movement

49
Q

Antinode

A

Point on a standing wave with maximum amplitude

50
Q

The main distinction between progressive and stationary waves

A

Progressive waves transfer energy whereas standing waves store energy

51
Q

How stationary waves work in air columns

A

Nodes at closed ends and antinodes at open ends

52
Q

How to produce stationary waves with microwaves

A

Set up a microwave transmitter and place a metal plate in front of it to reflect the microwaves. Between these you can place a microwave receiver to observe the stationary wave

53
Q

Distance between adjacent nodes

A

λ/2

54
Q

Distance between adjacent node and antinode

A

λ/4

55
Q

Resonant frequency

A

A frequency of wave that for a given system will produce an exact number of half wavelengths along the system

56
Q

Length of the system when vibrating at the third harmonic with nodes at both ends

A

3λ/2

57
Q

Fundamental mode of vibration

A

The 1st harmonic - the lowest possible resonant frequency

58
Q

Experiment to determine speed of sound using stationary waves

A

Set up a measuring cylinder with some water inside of it. Place a hollow plastic tube inside the measuring cylinder and get a tuning fork and record its frequency (it will be labelled on it). Sound the tuning fork above the cylinder and move the plastic tube up and down. At certain heights, a loud sound should be emitted, which means that you have found a harmonic. To find the 1st harmonic, find the smallest distance between the top of the water and the top of the plastic tube that creates this sound. This distance will then be λ/4 and the speed of sounds can then be calculated

Physics (AS) (14 decks)

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