Physics Lab Final - Speed of Sound

Define Standing wave

A special type of wave that is formed due to the wave interference of two waves of the same frequency and the same amplitude undergoing superposition as they travel in opposite directions. A wave that strikes a surface and reflects back upon itself will provide such a condition. A standing wave is composed of locations of maximum constructive interference and points of maximum destructive interference. Standing waves in a string are produced by a series of periodic "shakes." The antinodes have displacement up and then down, then up, then down.

What is a standing wave?

A special type of waves called standing waves occur when two waves of the same frequency and amplitude traveling in opposite directions interfere. It is called "standing" because it stands still at its position. The node is the point where maximum destruction of the two waves occurs. The antinode is the point where maximum construction occurs.

Define Longitudinal waves

A wave in which there is a displacement of the molecules of the transmitting medium parallel to the direction of energy propagation (to and fro). In a longitudinal wave there are alternate regions where the molecules are closer together than normal (compressions) and regions where they are further apart than normal (rarefactions).

What is the theory behind a wave?

A wave is a means of energy transport. It can be described as a cycle, since it repeats itself. The length of one full cycle is called wavelength. The period is the time required for one complete cycle. A fundamental property of waves is frequency, which is the number of cycles per unit of time.

Define wave

A way by which energy is transported from one location to another.

Pre-lab: 1. Define wavelength, λ and amplitude, A.

Amplitude is the amount of displacement of the wave from midline. Wavelength is the distance from one point on the wave to the next point.

v = 331.4 + 0.60T is one way to find the speed of sound if the temperature is known. What is another way?

Another way is to use some properties of the waves. Since sound is a longitudinal wave, it should have the property of interference, which is that two or more waves can occupy the same space at the same time.

Define sound waves

Energy transmitted from a vibrating object through an elastic medium. Sound waves are longitudinal waves through solids, liquids, and gases.

Frequency is ________proportional to period. What is the equation?

Frequency and period are inversely proportional

What determines how fast sound will travel?

How quickly the molecules react to this compression and rarefaction determines how fast the sound travels. For instance, in solids and liquids the molecules are close together. In gases the molecules are far apart and do not respond quickly to the vibration.

What happens if a tuning fork is held over a tube open at top and closed at bottom?

If a vibrating tuning fork is held over a tube open at the top and closed at the bottom, it will send air disturbances made up of compressions and rarefactions down the tube. A sound wave is thus formed in the air column. There will always be a node at the reflecting end. By adjusting the length of the air column, you can locate certain lengths that result in a standing wave and a sound that is more intense than the tuning fork by itself. This is the phenomenon known as resonance and will occur only when an antinode of the standing wave is located at the open end of the tube.

2. What is the wavelength of a sound wave with a velocity of 344 m/s and a frequency of 32 Hz? Or of 25 Hz?

v = (frequency)(wavelength) 32Hz Wavelength = 10.75 m 25Hz Wavelength = 13.76 m

2. What is the speed of sound in air when the temperature is 32 degC?

v = 331.4 + 0.60(32 degC) = 350.6 m/s

3. The speed of sound is temperature dependent and can be found using the experimentally determined relation v= 331.4 + 0.60 T. What is the velocity of a sound wave at T=24 degC?

v = 331.4 + 0.60T v = 331.4 + 0.60(24 deg C) v = 345.8 m/s

What are the tools used in the experiment?

Resonance tube apparatus Meter stick Celsius thermometer Two tuning forks of different frequencies Rubber hammer

How does sound travel differently in solids, liquids and gases?

Sound travels about 15 times faster in most solids and about 4 times faster in liquids than it does in air. Molecules in gases are very sensitive to temperature. The higher the temperature the faster they travel. The faster they travel, the more readily they respond to vibrations. Thus, sound travels faster in hot air than in cold air.

How does sound travel?

Sound travels as a wave. Since it is a wave, there is a wavelength and a frequency associated with sound as well as a velocity. Sound is the result of an object vibrating, and the frequency of this vibration is the frequency of sound. (The frequency determines the pitch that we hear.) Sound is a compressional wave. As the sound energy moves through air, it compresses and rarefies the medium in the direction of travel.

Define Amplitude

The amount of displacement from rest position or zero disturbance. The greater the amplitude the greater the intensity of the sound.

Define Intensity

The amount of energy transmitted by a wave each second per unit area. This is the amount of power per unit area. For a person with normal hearing an increase in the intensity of an audible tone results in a louder sound.

What is the audible range for humans?

The audible range for humans is from about 20 Hz to 20,000 Hz.

What is the equation that describes resonance

The distance between successive points at which resonance occurs, when the length of the tube is changed, gives the exact value of the half wave length: resonance (2) -resonance (I) = 3λ/4 - 1λ/4 = 2λ/4 = λ/2 (half wave length)

Frequency is a direct indication of?

The frequency is a direct indication of the wave energy.

What is the equation that describes frequency?

The important relationship that combines the frequency and the wavelength is through the wave speed v, where

Define Antinode

The locations of maximum constructive interference in a standing wave. Antinode to antinode is 1/2wavelengthA. ( 1⁄2 λ )A) Distance from a node to an antinode is 1/4 wavelengthA (( 1⁄4 λ )A).

What is an amplitude?

The maximum displacement from the equilibrium line or position is called the amplitude. When you change the volume of your radio, you are changing the amplitude.

Define Frequency

The number of vibrations that occur in one second of time. The unit for frequency (f) is the Hertz. One Hertz is equal to one vibration per second (vps) or one cycle per second (cps).

Define Phase

The phase relationship between two waves is a means of comparing their displacement with each other. Two identical frequencies that are in phase will always have constructive interference and the two tones combined will result in a more intense sound. If there is a phase difference, destructive interference will occur. Maximum destructive interference occurs when there is a phase difference of 180 deg. This means that two waves of the same amplitude would have a compression of one combining with a rarefaction of the other to result in zero amplitude or silence.

Define speed

The rate of motion (distance per unit time) of a wave. It depends upon the media through which the wave is traveling. Sound waves travel the fastest in elastic solids and slowest in gases. Speed is the magnitude of the wave velocity.

What is the relationship between temperature and velocity?

The relationship between temperature and velocity is v = 331.4 + 0.60 T This equation shows that at a temperature of T = 0 deg Celsius, sound travels at 331.4 m/s, and it speeds up or slows down 0.60 m/s for every degree of temperature change.

How is the resonance apparatus set up?

The resonance apparatus used in this experiment (see Fig. 6) consists of a glass tube 100 cm long, sealed into a metal cup at the bottom and mounted on a heavy tripod base. A metal supply tank is connected to the support rod by means of a clamp that permits rapid adjustment. A tuning fork is held directly above the tube to produce the driving sound wave.

3. If a sound wave passes from air into a solid for transmission, what will happen to the speed of wave?

The speed of wave will increase as it passes from air into a solid. This is as a result of sound waves passing faster through solids than air.

Define Period

The time required for one vibration.

Define Wavelength

The wavelength (λ) of a wave is the distance from one point in the wave to the next corresponding point.

Wavelength, frequency have units of?

The wavelength has the units of length, and the frequency unit is length of wavelength per second which is usually called Hertz.

How does resonance occur?

Thus, when a tuning fork is held over a tube closed at one end, resonance will occur if standing waves are set up with a node at the closed end and an antinode near the open end of the tube. This can take place if the length of the tube is very nearly an odd number of quarter wavelengths of the sound waves produced by the fork. Hence, resonance will occur when L = λ/4, 3λ/4, 5λ/4, etc., where L is the length of the tube and A is the wavelength of the sound waves in air

What was the purpose of the experiment?

To measure the speed of sound at room temperature and compare the value with a theoretical value, based on temperature.

Define Periodic waves

Waves created when the vibrating object repeats its motion at a constant rate.

Define Interference

Waves have a property that matter normally does not have. Waves can occupy the same place in space at the same time. This is called superposition. When two or more waves superpose, interference takes place. The amplitudes of the waves will constructively interfere to give a change in amplitude. A compression plus compression, or rarefaction plus rarefaction, will result in an increase in amplitude. A region of a compression and a rarefaction in the same place at the same time will result in a smaller amplitude than either of the two individual waves has.

Waves have two major types - what are they?

Waves, however, have two major types: longitudinal and transverse. Longitudinal waves are the ones where molecules of the transmitting medium move along the direction of the wave propagation. Transverse waves, on the other hand, have perpendicular motion. Sound is an example of a longitudinal wave, and light is a transverse wave. Unlike light, which can exist in a vacuum, sound waves require a medium to transfer them; thus their velocity varies according to the medium. Even in air, the speed of sound is found to depend on the temperature.

In this experiment - how was a closed air column obtained

In this experiment a closed air column of variable length is obtained by changing the level of the water contained in a glass tube. The length of the tube above the water level when resonance occurs is the length of the vibrating air column.

b. To the length necessary for resonance

Increases

Post Lab: 1. What changes will occur when there is an increase in the temperature in room a) to speed of sound?

It will increase the velocity of sounds

c. To the frequency of the tuning fork?

No change

Define Resonance

One object is set into vibration due to the presence of another vibrating object. Usually occurs between two objects of similar frequency and will result in a more intense sound.