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Physics > Waves: Sound/Light > Flashcards

Waves: Sound/Light Flashcards

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1
Q

Mechanical wave

A

wave that needs a medium to travel through e.g. sound waves, water waves

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2
Q

electromagnetic wave

A

does not need a medium to travel through e.g. visable light, x-rays

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3
Q

periodic travelling wave

A

periodic disturbance that travels outward from a source, transferring energy from the source to other places

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4
Q

transverse wave

A

wave where the direction of vibration is perpendicular to the direction in which the wave is travelling

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5
Q

longitudinal wave

A

wave where the direction of vibration is parallel to the direction in which the wave is travelling e.g. sound waves

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6
Q

amplitude of wave

A

height of wave from undisturbed point to crest

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7
Q

oscillation/cycle

A

period
1 crest and 1 trough

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8
Q

wavelength

A

distance from trough to trough/crest to crest

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9
Q

frequency

A

number of cycles passing any point per second

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10
Q

unit of frequency

A

Hertz (H) - 1Hz=1 cycle per sec

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11
Q

wave phenomena

A
  1. reflection
  2. refraction
  3. diffraction
  4. interference
  5. polarisation
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12
Q

c=fλ

A

c=speed
f=frequency
λ=wavelength

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13
Q

reflection

A

bouncing of waves off an obstacle in their path

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14
Q

refraction

A

changing of direction of a wave when it enters a region where its speed changes e.g. hear better on cold night

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15
Q

diffraction

A

sideways spreading of waves into the region beyond a gap or around an obstacle

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16
Q

constructive interference

A

2 waves meet and resulting amplitude is greater than the amplitude of each individual wave

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17
Q

destructive interference

A

where 2 waves meet and resulting amplitude is less than the amplitude of each individual wave
note: when trough meets crest the waves completely cancel each other out - completely out of phase

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18
Q

coherent sources

A

constant phase difference or in phase
they will have same frequency

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19
Q

nodal lines

A

lines in interference pattern where there is total destructive interference

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20
Q

antinodal lines

A

where constructive interference occurs

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21
Q

polarisation

A

restriction of waves to vibrating in a certain plane

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22
Q

stationary waves

A

amplitude of wave at every point is constant: no net transfer of energy.
occurs when 2 periodic travelling waves of same amp/frequency moving in opposite directions meet

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23
Q

node to node

A

λ/2

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24
Q

antinode to node

A

λ/4

25
Q

doppler effect

A

apparent change in frequency of waves due to the motion of the source/observer

26
Q

doppler effect uses

A

red/blue shift
gardaí speed traps

27
Q

source moving towards observer

A

f’=fc/c-u

28
Q

source moving away from observer

A

f’=fc/c+u

29
Q

red shift

A

tells us if a star is moving away from us (red has longest λ)
blue shift moving towards us

30
Q

overtones

A

multiples of a certain frequency
2f=1st overtone
3f=2nd

31
Q

harmonics

A

multiples of a certain frequency
f=fundamental frequency/1st harmonic
2f=2nd harmonic

32
Q

loudness

A

depends on the amplitude of the sound wave (higer amp. = louder)

33
Q

pitch

A

depends on the frequency of the sound wave. as frequency increases so does pitch

34
Q

quality

A

depends on the number of overtones present and the relative strengths of the overtones present

35
Q

frequency limits of audibility

A

highest and lowest frequencies that can be heard by a normal human ear
20Hz-20kHz

36
Q

natural frequency

A

the main frequency that an object will vibrate at if free to do so

37
Q

resonance

A

this is when a periodic force is applied to an object and has a frequency the same as or very near to the object’s fundamental frequency. this causes the body to vibrate with a very large amplitude

38
Q

sound intensity at a point

A

the rate at which sound energy is passing through unit area at right angles to the direction in which the wave is travelling at that point
I=P/A
unit: Wm^-2

39
Q

threshold of hearing

A

smallest sound intensity detectable by the average human ear at a frequency of 1kHz
it is 1×10^-12 Wm^-2

40
Q

frequency response of the ear

A

the average human ear is most sensitive between 2kHz and 4kHz

41
Q

Sound intensity level

A

scale that measures the amount of energy carried per sec into your ear
unit: decibels (dB)

42
Q

sound intensity to decibels

A

when sound intensity doubles sound intensity level (dB) increases by 3dB

43
Q

fundamental frequency of a string

A

when a string vibrates with an antinode at its centre and a node at each end
f= 1/2l(√T/µ)

44
Q

open pipe and harmonics

A

all harmonics present

45
Q

closed pipe harmonics

A

only odd harmonics possible

46
Q

grating constant

A

d=1/x where x=lines per mm
distance between 2 adjacent skits on grating

47
Q

zero order diffracted image

A

if light is passed through the diffraction grating and then passed through a convex lens all the light is brought together to form a very bright line

48
Q

first order diffracted image

A

first bright line to left/right of zero order

49
Q

monochromatic light

A

light that only has one frequency e.g. sodium only made up of orange light

50
Q

dispersion

A

the breaking up of white light into different wavelengths/colours

51
Q

recombination

A

bringing together the different wavelengths of light to make white light

52
Q

primary colours

A

red, green, blue

53
Q

secondary colours

A

yellow, cyan, magenta

54
Q

complementary colours

A

red + cyan
green + magenta
blue + yellow
(mix to give white)

55
Q

electromagnetic spectrum

A

from longest to shortest wavelength:
radio waves, infra-red, visable light, ultraviolet, x-rays, gamma rays

56
Q

UV light properties

A
  1. wavelength between 0.4µm and 5nm
  2. causes fluorescence in certain substances (substance absorbs UV and emits visable light)
  3. causes sunburn, cancer, harms eyes
  4. causes photo-emission
57
Q

infrared light properties

A
  1. wavelength between 0.7×10⁶m and 1mm - emitted by all hot bodies
  2. affects photographic plates: can take photos in dark, fog/mist, used by military rescue and doctors to diagnose abnormalities in body
  3. causes substances to heat up if it falls on them
58
Q

diffraction grating formula

A

nλ=dSinQ

n=order
d=grating constant

59
Q

stress polarisation uses

A

used by engineers to find stress in components

Physics (12 decks)

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