Question on waves

[BabyBoomer]

I've been reading through two old physics books about waves.

Electromagnetic waves have an intensity that is proportional to the square of their amplitude. I = e_ocE² W/m²

Where e_o is the permitivity of space, c is the speed of light and E is the amplitude of the field.

 

I'm not sure that i understand this, but in both the books it derives this result from a volume builit up from the wavelength of the wave and it's called the "unit volume".

 

Does this mean that this intensity is only for the volume occupied for a particular wavelength as the wave passes through an area of one side of the cube? So that this does not show the whole picture because any wave should have the energy also related to the square of it's frequency?

There must be an equation that shows how both the frequency as well as the amplitude is related to intensity?

I'm also thinking of the photon equation here, E = hf. So frequency has to count for an EM wave somehow, although i'm not exactly sure how the wave's photons relate to field strength but it does relate to the frequency of the EM wave.

I have two physics books and this is not shown in either of them, so i'm not sure if i'm on the right track here?

 

Thanks in advance.

[swansont]

I've been reading through two old physics books about waves.

Electromagnetic waves have an intensity that is proportional to the square of their amplitude. I = e_ocE² W/m²

Where e_o is the permitivity of space, c is the speed of light and E is the amplitude of the field.

 

I'm not sure that i understand this, but in both the books it derives this result from a volume builit up from the wavelength of the wave and it's called the "unit volume".

 

Does this mean that this intensity is only for the volume occupied for a particular wavelength as the wave passes through an area of one side of the cube? So that this does not show the whole picture because any wave should have the energy also related to the square of it's frequency?

There must be an equation that shows how both the frequency as well as the amplitude is related to intensity?

I'm also thinking of the photon equation here, E = hf. So frequency has to count for an EM wave somehow, although i'm not exactly sure how the wave's photons relate to field strength but it does relate to the frequency of the EM wave.

I have two physics books and this is not shown in either of them, so i'm not sure if i'm on the right track here?

 

Thanks in advance.

 

The volume defined by the wavelength is related to the frequency. A higher-frequency wave will have a smaller unit volume, so the energy density (for a constant volume) will be larger.

[BabyBoomer]

The volume defined by the wavelength is related to the frequency. A higher-frequency wave will have a smaller unit volume, so the energy density (for a constant volume) will be larger.

 

OK thanks, that sounds like good logic.

So what is the intensity equation for an EM wave showing the frequency?

it should be proportional to f²E² ?

[swansont]

So what is the intensity equation for an EM wave showing the frequency?

it should be proportional to f²E² ?

 

It's not going to show up explicitly in the intensity as you've expressed it, only the power density.