# speed, frequency, wavelength

#### batista_123

##### Junior Member
10+ Year Member
7+ Year Member
how do you know when f, v, and wavelength change?
in sounds, the only way to change the speed is to change the medium, correct?
so when the frequency changes, the wavelength changes but speed stays the same?
what about electromagnetic waves like light? does the frequency ever change? what about speed? what about wavelength?
I am just confused because i dont know when these change and when the dont. thanks

Last edited:

#### Hemichordate

##### Peds
10+ Year Member
Also, does density change the velocity?

#### ezsanche

##### Full Member
10+ Year Member
5+ Year Member
how do you know when f, v, and wavelength change?
in sounds, the only way to change the speed is to change the medium, correct?
so when the frequency changes, the wavelength changes but speed stays the same?
what about electromagnetic waves like light? does the frequency ever change? what about speed? what about wavelength?
I am just confused because i dont know when these change and when the dont. thanks

Sounds-
The sound wave velocity is indeed dependent on the medium. Specifically the wave velocity depends on the medium elasticity and its inertia. The following equation relates the wave velocity of sound traveling through a string to the tension (the elasticity aspect of a string) and the mass per unit length (the inertia aspect of a string).

V= (T/u)^1/2

where T is the tension
u= the mass per unit length.

As you can see you can increase the speed if you by making the medium "stiffer" or by making it ligther. This concept applies to all mediums not just strings.

The speed of sound traveling through gas (air) is also dependent on the gas temperature. As temperature increases then so does the velocity of sound. You do not need to know the exact equation for the mcat just this simple concept.

Frequency and Wavelength-

Frequency stays constant no matter what medium the wave is traveling through. The only thing that changes is the Wave velocity and the wavelength. These qualities can either increase or decrease depending on the type of medium and the type of wave (mechanical or electormagnetic)

#### batista_123

##### Junior Member
10+ Year Member
7+ Year Member
Sounds-
The sound wave velocity is indeed dependent on the medium. Specifically the wave velocity depends on the medium elasticity and its inertia. The following equation relates the wave velocity of sound traveling through a string to the tension (the elasticity aspect of a string) and the mass per unit length (the inertia aspect of a string).

V= (T/u)^1/2

where T is the tension
u= the mass per unit length.

As you can see you can increase the speed if you by making the medium "stiffer" or by making it ligther. This concept applies to all mediums not just strings.

The speed of sound traveling through gas (air) is also dependent on the gas temperature. As temperature increases then so does the velocity of sound. You do not need to know the exact equation for the mcat just this simple concept.

Frequency and Wavelength-

Frequency stays constant no matter what medium the wave is traveling through. The only thing that changes is the Wave velocity and the wavelength. These qualities can either increase or decrease depending on the type of medium and the type of wave (mechanical or electormagnetic)

so you mean frequency never changes? if any mcat choice says frequency changes, then it is wrong?

#### ezsanche

##### Full Member
10+ Year Member
5+ Year Member
If a wave is refracting (moving from one medium to another medium) then the frequency always remains constant. Only the wave velocity and the wavelength changes.

#### inaccensa

##### Full Member
10+ Year Member
Sounds-
The sound wave velocity is indeed dependent on the medium. Specifically the wave velocity depends on the medium elasticity and its inertia. The following equation relates the wave velocity of sound traveling through a string to the tension (the elasticity aspect of a string) and the mass per unit length (the inertia aspect of a string).

V= (T/u)^1/2

where T is the tension
u= the mass per unit length.

As you can see you can increase the speed if you by making the medium "stiffer" or by making it ligther. This concept applies to all mediums not just strings.

The speed of sound traveling through gas (air) is also dependent on the gas temperature. As temperature increases then so does the velocity of sound. You do not need to know the exact equation for the mcat just this simple concept.

Frequency and Wavelength-

Frequency stays constant no matter what medium the wave is traveling through. The only thing that changes is the Wave velocity and the wavelength. These qualities can either increase or decrease depending on the type of medium and the type of wave (mechanical or electormagnetic)

I thought the frequency always remains constant with light. The velocity of light always decreases when travelling from high refractive index to low (air to water) the frequency will remain constant and the wavelength increase.

Sound waves on a string are dependent on the tension and mass/length & in liquids on density and gases on pressure and temp. If the velocity changes here, does the frequency remain constant? Then for open, closed pipes, shouldn't the frequency remain constant, since they are in the same medium.

#### dragon529

##### MS-III
10+ Year Member
Can someone explain how does the velocity of both light and sound change when traveling through different refractive index? Do they work the same way? For both cases, frequency stays constant while wave speed and wavelength change?

#### inaccensa

##### Full Member
10+ Year Member
Can someone explain how does the velocity of both light and sound change when traveling through different refractive index? Do they work the same way? For both cases, frequency stays constant while wave speed and wavelength change?

With respect to light, this is how i understand it.
C =3*10^8 m/s is the maximum velocity of light. When n=1 for vacuum, the n=c/v implies that velocity is maximum. Thus when the refractive index increases, v must decrease.

Sound waves are confusing to me. There are many factors depending on which medium it travels. velocity is proportional to the elastic/ inertial factor
Solids = tension/mu^ 1/2
liquids = bulk modulus/density^1/2
gases = pressure/ density ^1/2
Also with increasing temp, velocity increases. I think that is because the kinetic energy increases.

But like i had asked earlier, if the frequency remains the same for sound waves, how do you explain the different frequencies of wave in an open, closed pipe?

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