photon has momentum?

[superflya]

just a random question i came across, had me puzzled 

and btw physics board was kinda dead, not cool 

[TrueTears]

yeah man, p =h/lambda

it has no mass tho, so don't ask me why it still has momentum, all i know is that it just does from my VCE physics knowledge.

[superflya]

lol yea i get that p=h/lambda but the answer is given in

wtf theres no mass, kg? ahah this is bull

[Edmund]

where the units for Plank's constant is J.s, wavelength is m, Joules is equivalent to N.m, Newtons is equivalent to kgms^-2

[QuantumJG]

just a random question i came across, had me puzzled 

and btw physics board was kinda dead, not cool 

Yes photons do have momentum. This momentum is given by;



A photon can act like a particle and it can also actually change the motion of something (I.e. Photons can collide with objects and change their velocity). The thing with quantum mechanics is that you can't apply classical mechanics to these situations.

There is also the Heisenberg uncertainty priciple which states:



Which says the uncertainty in momentum multiplied by the uncertainty in position must be greater than or equal to h divided by four pi (aka h-bar on 2).

You will learn about the photon in unit 4 physics and it's really fun.

As for physics posts you probably won't see many for there is only 4 people I know on VN who are majoring in physics in uni. At UoM there is really only 30 students who will do a master of science in physics.

[moekamo]

thats why some people prefer to use the unit (Newton-Second) when talking about photons since they have no mass, this unit avoids mention of a mass unit... even though it is still the same...

[superflya]

thanks, makes more sense guys

[/0]

I think it has to do with Mass-Energy equivalence, as given in . I'm not completely sure about this, but I think general relativity says that mass and energy are really the same thing. In particle physics, the masses of particles are usually given in electronvolts instead of kilograms.
That's what's so awesome about advanced physics... everything just comes together so beautifully

[appianway]

I don't think it's E=mc^2 exactly, but I think it's to do with the relationship between energy and 4-momentum. The energy of a photon can be given by E= hf = hc/lamnda, and p=E/c.

Edit: I love the energy/mass thing. I love relativistic collisions and the changes in mass that often occur.

[/0]

I don't think it's E=mc^2 exactly, but I think it's to do with the relationship between energy and 4-momentum. The energy of a photon can be given by E= hf = hc/lamnda, and p=E/c.

Edit: I love the energy/mass thing. I love relativistic collisions and the changes in mass that often occur.

Yeah I think the full form of is something like



Which reduces to for a massless particle and for a stationary particle... man i can't wait till i do general relativity

[Edmund]

For relativistic motion, the energy of a body (rest mass of m),
 


So I could say m=0


 


And the energy of a photon is so,
 


EDIT: /0 beat me

[appianway]

Yeah, /0, that's the full form. I usually just express it as gamma*mc^2, with mc^2 representing the rest mass and (gamma -1)mc^2 being the kinetic energy, but it's nice to go over the more detailed explanation of why E/c = p for the photon.

[QuantumJG]

I don't think it's E=mc^2 exactly, but I think it's to do with the relationship between energy and 4-momentum. The energy of a photon can be given by E= hf = hc/lamnda, and p=E/c.

Edit: I love the energy/mass thing. I love relativistic collisions and the changes in mass that often occur.

Yeah I think the full form of is something like



Which reduces to for a massless particle and for a stationary particle... man i can't wait till i do general relativity

That formula rings bells for me.

[Edmund]

I don't think it's E=mc^2 exactly, but I think it's to do with the relationship between energy and 4-momentum. The energy of a photon can be given by E= hf = hc/lamnda, and p=E/c.

Edit: I love the energy/mass thing. I love relativistic collisions and the changes in mass that often occur.

Yeah I think the full form of is something like



Which reduces to for a massless particle and for a stationary particle... man i can't wait till i do general relativity

That formula rings bells for me.

Physics 1 =/

Lots of bad memories

[/0]

I wish I studied harder for physics 1 & 2... I definitely don't think I got the most out of the course

 stupid vce... if only I didn't have to do it at the same time