# Intensity of Waves

#### Dr Gerrard

10+ Year Member
7+ Year Member
Does the intensity of a wave depend on frequency?

I have one equation where I is proportional to both amplitude and frequency squared.

But I often times come across a problem where they say it is not. Are they wrong?

Bonus Question: When a wave enters a new medium, is it true that only the wavelength changes? This is for both sound and light.

#### ezsanche

10+ Year Member
5+ Year Member
I beLIEve that the equation that you are referring to is the one written below.

I=1/2p(w^2)(A^2)v

where
p = density fo the medium
w= angular frequencey or 2x(pi)xf where f= frequency
A= amplitude
v= wave velocity

So from this equation you can clearly see that the intensity is dependent on the square of the frequency for all waves.

Bonus: Frequency stays constant for all medium. However a wave may speed up or slow down depending on what medium it is traveling in. Since the below equation most hold true:

V= Wavelength x Frequency

The wavelength changes when a wave enters a new medium.

#### SuperSaiyan3

7+ Year Member
I beLIEve that the equation that you are referring to is the one written below.

I=1/2p(w^2)(A^2)v

where
p = density fo the medium
w= angular frequencey or 2x(pi)xf where f= frequency
A= amplitude
v= wave velocity

So from this equation you can clearly see that the intensity is dependent on the square of the frequency for all waves.

Bonus: Frequency stays constant for all medium. However a wave may speed up or slow down depending on what medium it is traveling in. Since the below equation most hold true:

V= Wavelength x Frequency

The wavelength changes when a wave enters a new medium.
what??!?! You have to know this formula? I have NEVER seen such a thing.

Like never. Never in my life. Not in kaplan, not anywhere. Do you need to memorize this stuff??!

Btw, INTENSITY correlates with AMPLITUDE, aka the "loudness" of sound. Therefore, loudness has to do with intensity and this depends on the interference of the waves. Is it constructive or destructive?
Frequency correlates with PITCH.

That should be all you need to know. The equation you have there is ridiculous.

#### SuperSaiyan3

7+ Year Member
Bonus Question: When a wave enters a new medium, is it true that only the wavelength changes? This is for both sound and light.
I'm going for the bonus mark.

When a wave enters a NEW medium, the only thing that DOESN'T change is the velocity.

I don't feel like explaining any further so take my word for it if this question ever comes up on the test.

#### G1SG2

10+ Year Member
5+ Year Member
I'm going for the bonus mark.

When a wave enters a NEW medium, the only thing that DOESN'T change is the velocity.

I don't feel like explaining any further so take my word for it if this question ever comes up on the test.
I think you mean the frequency. The velocity of a wave depends upon the medium, and that is subject to change. For example, if light moves from air to water, the velocity will change (and the change is described by the index of refraction for water, which tells you the ratio of the velocity of the wave in vacuum to the velocity of the wave in water).

#### ezsanche

10+ Year Member
5+ Year Member
what??!?! You have to know this formula? I have NEVER seen such a thing.

Like never. Never in my life. Not in kaplan, not anywhere. Do you need to memorize this stuff??!

Btw, INTENSITY correlates with AMPLITUDE, aka the "loudness" of sound. Therefore, loudness has to do with intensity and this depends on the interference of the waves. Is it constructive or destructive?
Frequency correlates with PITCH.

That should be all you need to know. The equation you have there is ridiculous.
You dont need to know that equation for the MCAT. You just need to know that for all wave the intensity is proportional to the squares of the frequency and amplitude.

#### SuperSaiyan3

7+ Year Member
You dont need to know that equation for the MCAT. You just need to know that for all wave the intensity is proportional to the squares of the frequency and amplitude.
don't you mean INVERSELY proportional?

#### SonOfKrypton

10+ Year Member
don't you mean INVERSELY proportional?
No. It's directly proportional to the square of the frequency and the square of the amplitude. You're thinking inverse because you interpreted everything following the '2' in that equation as being in the denominator. It's not. It's '1/2' multiplied by all that mess.

#### RogueUnicorn

##### rawr.
7+ Year Member
I'm going for the bonus mark.

When a wave enters a NEW medium, the only thing that DOESN'T change is the velocity.

I don't feel like explaining any further so take my word for it if this question ever comes up on the test.
um. no.

#### Hemichordate

##### Peds
10+ Year Member
I beLIEve that the equation that you are referring to is the one written below.

I=1/2p(w^2)(A^2)v

where
p = density fo the medium
w= angular frequencey or 2x(pi)xf where f= frequency
A= amplitude
v= wave velocity

So from this equation you can clearly see that the intensity is dependent on the square of the frequency for all waves.

Bonus: Frequency stays constant for all medium. However a wave may speed up or slow down depending on what medium it is traveling in. Since the below equation most hold true:

V= Wavelength x Frequency

The wavelength changes when a wave enters a new medium.
Why does the frequency stay constant in different media but the wavelength changes?

#### RogueUnicorn

##### rawr.
7+ Year Member
beyond scope of mcat

#### ezsanche

10+ Year Member
5+ Year Member
Why does the frequency stay constant in different media but the wavelength changes?
You really dont need to know exactly why for the mcat just know it is because Energy must be conserved.

#### RogueUnicorn

##### rawr.
7+ Year Member
You really dont need to know exactly why for the mcat just know it is because Energy must be conserved.
this is only true for electromagnetic waves.

#### minutemen11

7+ Year Member
Does the intensity of a wave depend on frequency?

I have one equation where I is proportional to both amplitude and frequency squared.

But I often times come across a problem where they say it is not. Are they wrong?

Bonus Question: When a wave enters a new medium, is it true that only the wavelength changes? This is for both sound and light.
intensity is proportional to the square of BOTH the Amplitude and the frequency. It basically boils down to I=k* A^2*F^2 where k is a constant that you dont need to worry about for mcat.

"But I often times come across a problem where they say it is not. Are they wrong?"
Do you have an example of this?? Since frequency is always constant, the amplitude must be the only thing that changes when intensity changes. Even if the wavelength was made longer or shorter, (thereby making F lower or higher), the proportionality works because Amplitude is always independent of wavelength and frequency.