Energy in a photon/wave

[DrBO]

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Okay... so we all know the equation for energy of a photon is E=hf. So therefore if one wave has a higher frequency then it would also have a higher energy. My question involves wavelength and its effect on energy.

First, can this equation be rewritten as E=h v/wavelength ?

If so, then if a wave enters a different medium can i assume the energy will remain constant because v and wavelength will change in the same ratio?

Also, if this equation holds true, can i assume that a wave with a higher wavelength will have less energy?

This might seems straight forward, but for some reason I have written in my notes that a change in wavelength has no effect on the energy of a wave. Can someone please confirm or correct what I have stated here?

Also, can this energy equation be applied to sound waves?

 

[RogueUnicorn]

what you say is true. as long as you maintain the v/lamda relationship.

this equation is not applicable to sound

 

[549]

First, can this equation be rewritten as E=h v/wavelength ?
Yes. You're just replacing the frequency with an equivalent equation.

If so, then if a wave enters a different medium can i assume the energy will remain constant because v and wavelength will change in the same ratio?
Yes. When an EM wave enters a different medium, frequency never changes. Therefore, the energy will not change. No matter which equation you use, that will hold true.

Also, if this equation holds true, can i assume that a wave with a higher wavelength will have less energy?
Yes. Just think of radio waves vs UV waves. You won't get cancer from your radio (long wavelengths) but UV radiation is quite damaging (short wavelengths).

Hope this helps!

 

[inaccensa]

Okay... so we all know the equation for energy of a photon is E=hf. So therefore if one wave has a higher frequency then it would also have a higher energy. My question involves wavelength and its effect on energy.

First, can this equation be rewritten as E=h v/wavelength ?

If so, then if a wave enters a different medium can i assume the energy will remain constant because v and wavelength will change in the same ratio?

Also, if this equation holds true, can i assume that a wave with a higher wavelength will have less energy?

This might seems straight forward, but for some reason I have written in my notes that a change in wavelength has no effect on the energy of a wave. Can someone please confirm or correct what I have stated here?

Also, can this energy equation be applied to sound waves?

From the equation, V=f*lamda , f =V/lamda

Now E= Hf =hV/lamda or more commonly written as E = hc/lamda.

Larger wavelengths have low energy compared to the smaller wavelengths. Think about VIBGYOR, red light has the largest wavelength as less energy and smaller frequency. The wavelength of Blue light which is smaller than the red light, it has more energy. You can think of blue light being close to UV and gamma and thus higher in energy compared to the red light.

I do think that the energy of the wave remains constant despite it moving from one medium to another. In electromagnetic waves, the velocity and wavelength changes by the same ratio, while the frequency remains constant. If it moves to a higher index of refraction, the wavelength increases and the velocity decreases.So energy is conserved. The other way to think of it is " THAT THE FREQUENCY ALWAYS REMAINS CONSTANT" despite changing mediums. Since E =hf, h&f are constant and energy is the same.

correct me if i'm wrong here

 

[DrBO]

thanks for the quick responses everyone