Is light energy?

[Physiqs]

Is light energy?

if so, it cannot be created or destroyed according to the law of conservation of energy,

this video seems to say otherwise (look at 0:25-0:30)

 

link removed per rule 2.7

Edited February 8, 2016 by Phi for All
discussion members can't be forced to watch videos

[Strange]

Light has energy. That energy can be transformed into other sorts of energy. So, for example, when light is absorbed ("destroyed") by a dark surface, the energy of the light is changed into heat energy in the surface.

 

Also, conservation of energy is too specific. We now know that energy and mass are interchangeable So energy can be converted to mass and vice-versa. So it is the total mass-energy that is conserved.

[swansont]

Further, photon number is not conserved - you can make or destroy photons. The energy they have is conserved; anytime you create a photon it comes from somewhere, and if you destroy one the energy goes somewhere.

[Phi for All]

!

Moderator Note

Was your question answered, the misinformation sorted properly? I removed the video link since our rules state that we should be able to participate without clicking any links.

 

Does knowing that energy is a property of light change the direction of your questions?

[MigL]

There is a fair bit of the question that remains unanswered, and requires quite a bit of subtlety.

Energy is one of the properties that we associate with electromagnetic radiation.

But if you remove the property of energy from the EM wave, by reducing its frequency to zero, or lengthening its wavelength to infinity, what are you left with ???

 

We have the curious result that removing a 'property' of an effect, also removes the effect.

 

So, is the property equivalent to the effect ?

I.E. is light equivalent to energy ?

[swansont]

There is a fair bit of the question that remains unanswered, and requires quite a bit of subtlety.

Energy is one of the properties that we associate with electromagnetic radiation.

But if you remove the property of energy from the EM wave, by reducing its frequency to zero, or lengthening its wavelength to infinity, what are you left with ???

 

We have the curious result that removing a 'property' of an effect, also removes the effect.

 

So, is the property equivalent to the effect ?

I.E. is light equivalent to energy ?

How surprising is it the if the phenomenon is absent, the properties of the phenomenon also disappear?

 

But anyway, you're wrong. You can go to zero frequency and have a DC field. Which still has energy.

[MigL]

True: but I was originally thinking in terms of what happens to EMR at the event horizon of a BH ( to a distant observer )

And on further reflection the light's mass-energy is conserved, even though the light does 'disappear'.