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Physics 11 > Waves (Unit 1) > Flashcards

Waves (Unit 1) Flashcards

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1
Q

Equilibrium/Rest Position

A

a natural rest position of medium, such as slinky

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2
Q

Pulse

A

Disturbance that moves down a medium to create a wave

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3
Q

Wave

A

a disturbance that transfers energy over a distance

a wave is the motion of a disturbance

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4
Q

Periodic Motion

A

The vibration of the object is repeated over and over with the same interval each time - an object repeats a pattern of motion - it has wavelengths

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5
Q

Longitudinal Wave

A

Occurs when an object vibrates parallel to its axis

ex. sound waves

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6
Q

Transverse Wave

A

Occurs when an object vibrates perpendicular to its axis at the rest position
ex. a child swinging on a swing

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7
Q

Torsional Wave

A

Occurs when an object twists around its axis at rest position

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8
Q

Anatomy of a Wave

A

Staight Dashed Line - equilibrium position
Crest - maximum positive/upward displacement
Trough - maximum negative/downward displacement
Amplitude - distance from equilibrium to the maximum displacement

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9
Q

Wavelength (λ)

A

Distance between two consecutive similar points (ex. 2 crests or 2 troughs)
1 wavelength is made up of 1 crest and 1 trough

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10
Q

1 Cycle

A

One complete vibration/oscillation

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11
Q

Frequency (f)

A

Number of cycles per second; how many times a pulse passes a fixed point over time
Measure frequency in Hertz - cycles/second
f = # of cycles/time

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12
Q

Wave Period (T)

A

The time is takes for one cycle to complete

T = time/# of cycles

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13
Q

Relationship of Frequency and Wave Periods

A

They are reciprocals of each other
f = 1/T
T = 1/f

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14
Q

In phase

A

If objects have the same period and are passing through the rest position at the same time

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15
Q

Out phase

A

Objects don’t have the same period or they do but pass through the rest position at different times

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16
Q

Wave Equation

A 
Velocity = frequency * wavelength 
v = fλ
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17
Q

What determines frequency?

A

Source of disturbance is the ONLY thing that determines frequency

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18
Q

What determines speed?

A

Medium determines the speed of the wave

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19
Q

Boundary Behaviour

A

Behaviour of a wave as it reaches the end of its medium

A change in medium results in changes of wavelength and wave’s speed

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20
Q

Fixed End Reflection

A

Reflection from a rigid obstacle when a pulse is inverted

The reflected pulse has the same wavelength and speed as the incident pulse and amplitude is almost the same

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21
Q

Free End Reflection

A

Reflection where the new medium is free to move and there is no inversion
Reflected pulse is not inverted, is identical to incident pulse but travels in the opposite direction

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22
Q

Partial Reflection

A

Some of the energy is transmitted into the new medium and some is reflected back into the original medium

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23
Q

Less Dense -> Denser Medium

A

Part of the wave and its energy is reflected and part of it is transmitted
Transmitted pulse is upright, reflected pulse is inverted
The speed and wavelength of reflected wave remain the same, amplitude decreases.
The speed and wavelength of the transmitted pulse are both smaller than in the incident pulse.
Going from less dense → denser is like fixed end for reflected pulse
see pic on doc pg 4

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24
Q

More Dense -> Less Dense Medium

A

Going from more dense → less dense is like free end for reflected pulse
Reflected pulse is still upright and just has less amplitude
Transmitted pulse increases in wavelength and speed.

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25
Interference
When waves meet while traveling along the same medium
26
Constructive Interference
Both waves have positive amplitude or negative amplitude AT THE SAME TIME The waves will be added together and build each other up to make a greater amplitude in the medium, causing supercrest or spertrough
27
Destructive Interference
One wave has a positive amplitude, the other has a negative amplitude When the waves diminish each other and the amplitude of the medium is than in would have been for either of the interfering waves acting alone The two add together to decrease the amplitude, sometimes even make it 0 if positive and negative amplitudes are equal
28
Principle of Superposition
You can find the resulting amplitude of two interfering waves by adding the two amplitudes at any given point.
29
Reflection
When an incident ray encounters a barrier, it is reflected in the same angle Wavefronts - leading edge/front of a wave Wave rays - reflection waves Normal - straight line perpendicular to the barrier the wave hits; constructed at the point the incident wave ray hits the barrier Focal point - specific point where straight waves are reflected to in a parabolic reflector
30
Refraction
When a wave enters a new medium, it has a bending effect on the wave, so it’s angled
31
Diffraction
When waves pass through a small opening, it has a bending effect on the wave to make it fit
32
Interference of Waves in 2D
When two waves in 2D meet, their interference pattern includes areas of constructive and areas of destructive interference
33
Resonance or Mechanical Resonance
Resonance occurs when vibrations travelling through an object match the object’s natural frequency; The transfer of energy from one object to another having the same natural frequency Examples: music, swings, singing rods
34
Sympathetic Vibration
The response to a vibration with the same natural frequency When an object vibrates in resonance with another Ex. If an opera singer sings a note with the same natural frequency as that of a wineglass, the wineglass will start to vibrate
35
Standing Wave
Standing Waves are created when waves travelling in opposite directions have the same amplitude and wavelength It appears to be standing in one place because of the supercrests and supertroughs, even though it is two waves interfering as they pass through each other. It can be a wave interfering with its reflection
36
How can a wave interfering with itself can set up standing waves?
A reflected wave interferes with its incident wave. They both have the same source and cross the same medium with little loss of energy So, they have the same frequency, wavelength and amplitude
37
Node or Nodal Point (N)
Point that remains at rest | The nodes are equidistant and their spacing is equal to one-half of the wave-length of the interfering waves
38
Antinodes
Point midway between the nodes where maximum constructive interference occurs
39
Incident Pulse
The wave that goes towards the obstacle or new medium
40
Reflected Pulse
The incident pulse but it’s reflected back from the obstacle or medium
41
Transmitted Pulse
The pulse that goes through the new medium, only during change in medium
42
Sounds
A form of energy produced by rapidly vibrating objects and the energy stimulates the auditory nerve in the human ear, allowing us to hear sounds All sounds originate from vibrating objects Infrasonic: sounds less than 20Hz Ultrasonic: sounds higher than 20 000Hz Most young people can hear from about 20-20 000Hz
43
What type of waves are sound waves and its properties?
Longitudinal Waves Sounds require a medium to propagate; sound needs a material medium for its transmission In sound waves, a compression is an area of higher than normal air pressure and rarefaction is lower than normal air pressure If the amplitude of a sound wave is large, the sound seems loud—if small, the sound seems soft
44
Pitch
Related to the frequency of sound waves. As frequency increases, the pitch of a sound increases
45
Speed of Sound
Is slower than light; ~1/100000 the speed of light Speed depends on the medium, the pressure and the temperature Speed of sound in air at normal atmospheric pressure and 0C: 332m/s At constant pressure, if temperature increases, speed of sound increases. Every +1C, speed is +0.59m/s General Speed Equation: vs = 332 + 0.59t t = temperature in celsius
46
Speed of Sound in Different Mediums
Sound can be transmitted through solid, liquid or gas Speed of sound changes if medium or material changes The denser the material (air vs water), the faster sound travels In the same material (air), air will travel faster in the hotter medium (hot air) than the cold medium (cold air) because it has the same density but the hotter medium has more energy. Speed of sound in solid > liquid > gas
47
Intensity of Sound
Sound Intensity: power of a sound per unit area2/m2 Describes the conditions for the threshold of hearing, both lower and upper limits Unit to measure sound: bel (B). decibel (dB) is more common that bel (1dB = 10-1 B) 10-12 W/m2 (Watt per square metre) = 0 dB Decibel meter measures sound intensity Non-linear scale; 10dB up the scale is x10 the intensity (+10dB increases the intensity by tenfold) Ex. 10dB is 10 TIMES more intense than 0dB. 20dB is 10x more intense than 10dB. 10dB → 100dB = an increase of 109 (change of 90dB) or a billion times more intense Intensity of sound depends on power of the source and distance from the source Sound waves spread their wave energy over an increasing area, so intensity of a sound decreases as distance from the source increases.
48
Reflection of Sound Waves (Echoes)
Echoes: reflected sound wave; they’re produced when sound is reflected by a hard surface, such as a wall or cliff Echo can only be heard distinctly if the time interval between the original sound and the reflected sound is greater than 0.1s Sound waves conform to the laws of reflection
49
Sonar devices
Devices that use transmitted and reflected underwater sound waves to locate objects or measure the distance to the bottom of the water body
50
Echolocation
Location of objects through the analysis of reflected sound Example: A ship is using sonar to determine the speed of sound in water that has a depth of 120 m. The time for the wave to return is 0.16 s. V = d/t 240/0.16 = 1500m/s
51
Refraction of Sound Waves
When sound goes from air of 1 temperature to another (enters a new medium), sound waves refract Sound travels faster in warm air and will refract away from the normal when travelling from cold into warm air; If there’s warm air on top of cold air, the sound will move downward and the opposite will happen if cold air is on top
52
Refraction of Sound Waves
Waves are diffracted as they pass through narrow openings | Diffraction of a wave depends on its wavelengths and size of the opening
53
Interference of Sound Waves
It’s just like normal. Constructive and deconstructive interference occurs Read 7.8 for stuff about sounds from speakers and interference there
54
Beat
Periodic changes in sound intensity caused by interference between two nearly identical sound waves
55
Beat Frequency
The number of beats heard per second (unit: hertz) If the sources are within 7 Hz of one another, a pattern of increasing/decreasing loudness is heard fb = |f1 - f2| = # of beats / time
56
Doppler Effect
When a source of sound approaches an observer, the observed frequency increases; when the source moves away from an observes, the observed frequency decreases It is perceived frequency Perceived Frequency Equation on notes
57
Supersonic Travel
add stuff from textbook
58
Music vs Noise
Music: sound that originates from a source with one or more constant frequencies Noise: sound that originates from a source where the frequencies aren’t constant
59
Pure Tone
In music, a sound where only one frequency is heard
60
Octave
Sounds that differ in frequency by 2x
61
Frequency in String Instruments depend on: (+ their equations)
Vibrating Strings: The frequency of strings depends on the following factors Length(l) f1/f2 = l2/l1 Tension (F) f1/f2 = √F1/√F2 Diameter (d) f1/f2 = d2/d1 Density (D) f1/f2 = √D2/√D1 In stringed instruments, both ends are fixed(standing waves are set up)
62
Fundamental frequency (fo)
The lowest natural frequency of stringed instrument
63
Harmonics
Whole-number multiples of the fundamental frequency
64
Overtones
The resulting modes of vibration when a string vibrates in more than one segment emitting more than one frequency
65
Resonance in Closed Air Column
A closed air column has one closed end and one open end At the correct lengths, the waves are constrained at the fixed end and a node occurs; an antinode occurs at the open end Resonance occurs after a new node is formed In general, the length at which resonance occurs can be found via: Ln = (2n - 1)(λ/4)
66
Resonance in Open Air Column
when both ends are open, resonance occurs at lengths which have antinodes at their ends Since a pipe is open at both ends, resonance happens in both ends Length of Resonance: Ln = (nλ)/2

Physics 11 (1 decks)

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