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LC Physics > Vibrations and Sound > Flashcards

Vibrations and Sound Flashcards

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1
Q

What is the frequency of a vibrating object? and its unit of measurement

A

The number of cycles occurring per second. It’s measured in Hertz (Hz)

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2
Q

What form does sound travel in?

A

Wave

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3
Q

Explain acoustics

A

The science of designing theatres or concert halls with the correct balance of reflection and absorption of sound

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4
Q

What is reflection of sound

A

echo

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5
Q

How do we know sound waves undergo refraction

A

Sounds are heard clearer over water or on a cold

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6
Q

How do we know sound waves undergo diffraction

A

Can hear around corners

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7
Q

What is the relationship between the frequency and the vibrating source producing it

A

The frequency of sound is the same as that of vibrating source producing it.

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8
Q

What is the amplitude

A

The maximum displacement of any molecule from it’s rest position

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9
Q

What type of wave is sound

A

It needs a medium to travel through. It is a longitudinal wave- the molecules vibrate parallel to the direction in which the compressions and rarefactions travel.

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10
Q

What is the speed of sound in air

A

331m/s

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11
Q

What s the relationship medium density and the speed of sound in that medium

A

The denser the medium the greater the speed

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12
Q

What is an overtone

A

Frequencies are multiples of certain frequency
ex: f is a given frequency
2f is the first overtone
3f is the second overtone

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13
Q

What is loudness of a sound wave what depend on

A

It depends on the amplitude and frequency of a wave, The greater the amplitude the greater the loudness

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14
Q

What is pitch and what does it depend on

A

It depends on the frequency of the wave. The higher frequency the higher the pitch. The lower the frequency the lower the pitch

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15
Q

What is the quality of a note and what does it depend on

A

It depends on the number of overtones present in the note and the relative strengths of the different overtones present

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16
Q

What are the frequency limits of audibility

A

Highest and lowest frequencies that can be heard by a normal human ear. Range is 20 Hz- 20,000 Hz

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17
Q

What are frequencies above 20,000 Hz called

A

ultrasonic

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18
Q

What is the natural frequency

A

Any object free to vibrate will do so at a certain frequencies the predominate of which is it’s natural frequency of vibration

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19
Q

Explain resonance

A

If frequency of a periodic force is the same as it’s natural frequency the body will vibrate at a large amplitude. This phenomenon is resonance

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20
Q

Give four examples of resonance

A

Barton’s pendulum
Wire on a sonometer with a tuning fork
Buildings in an earthquake
Shatter glass, natural frequencies is the same as some high notes

21
Q

What is the threshold of hearing

A

The smallest sound intensity detectable by the average human ear at frequency of 1kHz

22
Q

What is sound intensity

A

It is the rate at a point which sound energy is passing through unit area at rights angles to the direction in which the sound is travelling at that point

23
Q

What is the unit of sound energy

A

Watt per square metre Wm^-2

24
Q

What is sound intensity level measured in

A

decibels (dB)

25
Q

What frequencies is the ear most sensitive between

A

2000Hz and 4000Hz

26
Q

When sound intensity in Wm^-2 is doubled what happens to the sound intensity level?

A

Increases by 3dB

27
Q

What is a sound level meter used for

A

It uses a dBA (Decibel adapted) scale, to take account of the vibration in the human ears response to sounds of different frequencies

28
Q

What damage can noise do and why noise protection needed

A

Partial deafness due to being exposed to loud sounds is incurable.Industry workers/farmers war ear protection when working with loud machinery

29
Q

Explain a string vibrating at it’s fundamental frequency

A

A string vibrating with an antinode at it’s centre and a node at either end (with no others) is vibrating at it’s fundamental frequency

30
Q

What is the relationship between the length of string and its fundamental frequency

A

Greater the length the lower the fundamental frequency. Fundamental frequency of a string is inversely proportional to it’s length.
f is proportional to 1/l

31
Q

How can F is proportional to 1/l be verified

A

With a sonometer - to investigate the variation of the fundamental frequency of a stretched string

32
Q

Explain harmonics

A

Frequencies which are multiples of a certain frequency F are harmonics. F is 1st harmonic and the fundamental frequency. 2f is the second harmonic etc…

33
Q

What is the formula for the fundamental frequency of a string

A

f= 1/2l (square root of T/mass per unit length)

34
Q

How is fundamental frequency proportional to Tension

A

f is proportional to the square root of T

35
Q

How is fundamental frequency proportional to mass per unit length

A

f is proportional to 1/square root of mass per unit length

36
Q

Explain how stationary waves act in a pipe closed at one end

A

There is a node at the base of the pipe.- molecules do not vibrate
The amplitude increases as you move up and there is an antinode at the top of the pipe- molecules vibrating with a max amplitude.

37
Q

How does resonance occur in a pipe

A

If pipe’s length is varied resonance will occur at certain lengths

38
Q

Explain how stationary waves act in a pipe open at both ends with an example

A

There must be an antinode at each end.
In open pipe all harmonics may be present.
Tin whistle is an example of a musical instrument which a column of air resonates in a pipe open at both ends

39
Q

In the experiment variation of the fundamental frequency of a stretched string with it’s tension how is the fundamental frequency determined

A

Changing tuning fork and adjusting tension until resonance is observed

40
Q

How would the measurements taken In the experiment variation of the fundamental frequency of a stretched string with it’s tension be shown on a graph

A

graph of f against graph of square root T as they are proportional

41
Q

How does the graph of frequency proportional to tension verify that relationship In the experiment variation of the fundamental frequency of a stretched string with it’s tension

A

there is a straight line through the origin

42
Q

How would the measurements taken In the experiment variation of the fundamental frequency of a stretched string with it’s length be shown on a graph

A

plot f compared to 1/l

43
Q

What is the relationship between fundamental frequency and length as shown in the experiment variation of the fundamental frequency of a stretched string with it’s tension be shown on a graph

A

f is proportional to 1/l

44
Q

In the experiment variation of the fundamental frequency of a stretched string with it’s tension how was tension measured

A

Newton balance

45
Q

In the experiment to measure the speed of sound in air how was the column of air adjusted, how was the frequency measured and how was the diameter measured

A

-Open pipe was raised for length
Read the frequency from the tuning fork
Diameter was measured using a vernier calipers

46
Q

In the experiment to measure the speed of sound in air how was it known the air column was vibrating at it’s first harmonic

A

The first time resonance - a loud sound is observed

47
Q

In the experiment to measure the speed of sound in air why do you need to measure diameter of the top of the tube

A

the wave partially exists above top of tube

48
Q

How would you find the speed in air doing the experiment to measure the speed of sound in air but not measuring the diameter

A

You would find the distance between two points of resonance and double this to find the wavelength. multiply wavelength by frequency to get speed

LC Physics (9 decks)

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