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BMAT Physics > waves > Flashcards

waves Flashcards

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1
Q

transfer of energy through waves

A
  • waves consist of a pattern of vibrations (oscillations).

- when the wave is absorbed it transfers energy to the object that absorbs it, but there is no transfer of matter

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2
Q

types of waves

A
  • transverse waves: vibration direction is perpendicular to wave direction
  • e.g. all EM spectrum waves
  • longitudinal waves: vibration direction is parallel to wave direction
  • e.g. sound waves, ultrasound waves
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3
Q

crest

A

top of the wave

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4
Q

trough

A

bottom of the wave

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5
Q

amplitude

A
  • half the height of the wave
  • a measure of how much energy the wave has
  • symbol: A
  • units: metres
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6
Q

wavelength

A
  • distance of one wave (from one crest to the next crest in transverse waves, distance between adjacent compressions/rarefactions in longitudinal waves)
  • symbol: upside down Y (lamda)
  • units: metres
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7
Q

frequency

A
  • number of waves produced in one second
  • symbol: f
    units: Hz
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8
Q

period

A
  • time taken to produce one wave
  • symbol: T
  • units: seconds
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9
Q

speed

A
  • distance travelled by wave in one second
  • symbol: v
  • units: ms-1
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10
Q

formulae (3)

A 
v = f x lamda
f = N/t 
T = 1/f
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11
Q

compressions and rarefactions

A
  • the pattern of vibration for longitudinal waves
  • compression: particles in the medium are pushed closer together as the wave passes (lines close together)
  • rarefaction: particles in the medium are pulled further apart as the wave passes (lines further apart)
  • distance between 2 adjacent compressions or 2 adjacent rarefactions = 1 wavelength
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12
Q

mechanical waves

A

-consist of vibrating particles, so can only move through a material medium (can’t travel through a vacuum)

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13
Q

electromagnetic waves properties

A
  • don’t need a material medium, so they travel through a vacuum
  • they always travel at the speed of light (3x10^8 ms-1) in a vacuum and air
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14
Q

EM waves types

A
  • Radio: ROGER (longest wavelength, lowest frequency)
  • Microwave: MOORE
  • Infra-red: INVENTS
  • Visible light: VERY
  • Ultra-violet: USEFUL
  • X-ray: XBOX
  • Gamma-ray: GAMES (shortest wavelength, highest f)
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15
Q

mechanical waves types

A
  • Sound
  • Ultrasound
  • Seismic waves: longitudinal and transverse vibrations of matter inside the Earth travelling outwards from earthquakes
  • Water waves: partly traverse, partly longitudinal
  • Waves on a string
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16
Q

prefixes

A

milli: 10^−3
micro: 10^−6
nano: 10^−9
kilo: 10^3
mega: 10^6
giga: 10^9

17
Q

refraction

A
  • the change of speed of light waves when light enters a new medium
  • incidence angle (i) angle between the normal and the incident ray
  • reflected angle (r) angle between the normal and the reflected ray
  • incidence ray=reflected ray
  • normal=line drawn perpendicular to the surface at a point where the ray hits the surface
18
Q

reflection from smooth and rough surfaces

A
  • if the surface is smooth all the normals are parallel to one another so all the waves are reflected in an orderly way
  • if the surface is rough the normals at each point are in different directions so each ray is reflected in a random direction
19
Q

refraction in different media

A
  • when waves enter a more dense medium, it slows down and refracts toward the normal (e.g. air to glass).
  • when waves enter a less dense medium, it speeds up it and refracts away from the normal (e.g. glass to air)
  • when leaving the object, the ray is parallel to the ray entering the object
20
Q

reflection affect on frequency, wavelength, speed and direction

A
  • reflection changes the direction of a wave

- reflection doesn’t change its speed, frequency and wavelength because the reflected wave remains in the same medium

21
Q

refraction affect on frequency, wavelength, speed and direction

A
  • refraction involves a change of wave speed
  • increasing wave speed (entering a less dense medium) increases wavelength
  • decreasing wave speed (entering a denser medium) decreases wavelength
  • frequency is unchanged
  • the direction of the wave changes unless the incident wave is travelling along the normal to the boundary
  • the greater the change in speed, the larger the refraction
22
Q

Doppler effect

A
  • source and observer at rest relative to one another: no change on wavelength or frequency
  • source and observer approaching one another: shorter wavelength, higher frequency
  • source and observer moving away from one another: longer wavelength, lower frequency
23
Q

Relationship between vibrations of source and sound produced

A
  • the sound waves have the same frequency as the vibrations of the source
  • the amplitude of the sound waves depends on the amplitude of the vibrations of the source
  • the speed of the sound waves is determined by the medium through which they travel (not by the source)
24
Q

ultrasound vs sound

A
  • sound has frequencies within the limit of human hearing ( < 20kHz)
  • ultrasound has frequencies above the limit of human hearing ( > 20kHz)
25
Q

loudness of a sound

A
  • depends on the amplitude of the sound waves

- the greater the amplitude, the louder the sound

26
Q

pitch of a sound

A
  • depends on the frequency of the sound waves

- the higher the frequency, the higher the pitch

27
Q

using sound reflection (echoes) to measure distance

A

𝑑=𝑣𝑡/2

28
Q

range of human hearing

A

-the human ear cannot detect sounds with frequencies <20 Hz or >20 kHz

29
Q

visible light

A

Visible light is subdivided into 7 regions:

  • red: RICHARD (longest wavelength, lowest frequency)
  • orange: OF
  • yellow: YORK
  • green: GAVE
  • blue: BATTLE
  • indigo: IN
  • violet: VAIN (shortest wavelength, highest frequency)
30
Q

X rays and gamma rays

A
  • X-rays are usually produced when fast moving electrons crash into a metal target and stop
  • Gamma-rays are usually produced by radioactive decay
  • X-rays and gamma-rays with the same wavelength are identical
31
Q

use of ultrasound

A

prenatal scanning

32
Q

use of infrared light

A

thermal imaging

33
Q

polarisation

A
  • when the vibrations of a transverse wave are restricted to one direction
  • all EM waves can be polarised
34
Q

sound waves entering a denser medium

A
  • speed increases

- wave refracts away from the normal

BMAT Physics (7 decks)

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