# A particle with a mass of 6 MeV has energy in Joules of 6c^2?

1. Jan 19, 2005

### DB

Just to clarify. A particle with a mass of 6 MeV has energy in Joules of 6c^2?
And a particle with an energy of 3 MeV has a mass of 3/c^2 kg?

And is there a way to convert this energy to a particle's charge?

2. Jan 19, 2005

### Norman

1 eV = 1.60219E-19 J

That is the correct conversion. You need to convert eV into Joules
Hope that helps.
Cheers

3. Jan 19, 2005

### chroot

Staff Emeritus
The electron-volt is a unit of energy, not mass. While people might say things like "a mass of 3 MeV," they actually mean the rest mass equivalent of 3 MeV of energy. In other words, they're implying "3 MeV / c^2." 3 MeV / c^2 is about 3 thousandths of a proton mass:

As for the first line of your post, a particle with a mass of 6 MeV (/c^2) has energy of 6 MeV. Your units are not consistent when you bring joules in the picture. If you want to use MeV/c^2 as your unit of mass, you need a conversion factor to use joules as your unit of energy. You can use MeV/c^2 for mass and MeV for energy, or you can use kilograms for mass and joules for energy, but you cannot mix them without doing a unit conversion.

- Warren

4. Jan 19, 2005

### chroot

Staff Emeritus
And, a particle's charge has nothing whatsoever to do with its mass or energy.

- Warren

5. Jan 19, 2005

### DB

Thanks guys, so your saying that I have to do a convertion to make kilograms equivilant to Joules? If so, how do I do that? (without using the google calculator for now)

6. Jan 19, 2005

### chroot

Staff Emeritus
Kilograms and joules are not the same thing -- you can't make them "equivalent." You can multiply kilograms by c^2 to get joules, though. What exactly are you trying to do here?

- Warren

7. Jan 19, 2005

### DB

Just my curiosity.
What I mean is, when you have a particle with energy 3MeV is it safe to say it has a mass of 3/c^2 Kg and that a particle with a mass of "6MeV" has an energy of 6c^2 Joules

8. Jan 19, 2005

### chroot

Staff Emeritus
Absolutely not, no. Didn't I just explain all of that to you?

- Warren

9. Jan 19, 2005

### DB

I don't quite understand it. If it is possible, how could you convert something with an energy in MeV to a mass in kilograms.

10. Jan 19, 2005

### chroot

Staff Emeritus
First, convert MeV to joules. Then, divide by c^2, with c in meters/second.

- Warren

11. Jan 19, 2005

### Norman

DB-
the problem is when you see mass given in units of MeV, and you are thinking that somehow this mass can be expressed in kg? Or are you trying to say you can change an Energy in MeV into mass?

Mass and energy are different on a very basic level- they are different dimensions. The units of each (mass in kg, energy in Joules) are related by the famous equation $E=mc^2$, that is what chroot has said. Mass and energy are not the same things. Their dimensions are related to each other through $c^2$ which has dimensions of $\frac{(distance)^2}{(time)^2}$. This notion of dimensionality is why you cannot relate time to mass, etc. Time is time, mass is mass, they are fundamentally different quantities. Just like mass and energy are different. Does this help?

12. Jan 19, 2005

### DB

Thanks a bunch.

13. Jan 20, 2005

### imran

what is electron indeed a wave or a particle.

i am at graduate level.first i was taught that e- is a particle.now it came to my note that it behaves as wave at some times.what's the exp which says so.
is it right to say e- is a wav-icle.in what kind of situations it behaves like so(as a particle some times and wave at another time).
what does the modren theory say?

14. Jan 20, 2005

### dextercioby

Nope,there's no such thing like a "wave-icle"... :tongue2: The particle-wave duality is something fundamental at quantum level and ot has been experimentally proven many times.

The interference and diffraction experiments with electron beams (a priori considered made up of "genuine" particles) proved that the electron behaves like a wave...Schroedinger assumed that fact to be real and he invented wave-mechancs,an elementary form of QM.

The "modern theory" took this wave-like behavior of elementary particles and built quantum field theory...Which gave pretty good results so far...

Daniel.

15. Jan 20, 2005

### vanesch

Staff Emeritus
Well, I have to say I like the expression :-)

In Newton's time, there were particles, which were associated with points in an Euclidean space.

In the 19th century, there were 2 things: there were still these particles (points in Euclidean space), and there were also "fields", which were mappings from E^3 into E^3 (in fact, they were mappings from a 4-manifold onto its fibre bundle, but that wasn't realized at that point)

And in the beginning of the 20th century, the quantum mess started.
There were, in the beginning, still these fields, with which people didn't know what to do, and there were still these "point-like particles" but which got a "wave" (field) associated with it, and people were then dancing between the "particle" and the "field" viewpoint (the mysterious wave-particle duality). Very fuzzy experience.

Then came along quantum field theory, first slowly and then more firmly:
"Everything is a quantum field". What's a quantum field ? It is a classical field, on which one applies the quantification procedures "as usual", and out of which comes... strangely, a behaviour as if it were build up of a kind of particles! Not really particles "points in E^3", but "quantum particles" which make that the interactions between the quantum fields always go into "lumps of momentum and energy" in such a relationship that E^ = p^2 + m^2. That's what remains of our "particle".

And then came (I only learned this recently !) Weinberg's view, which shows in fact, that we can AGAIN consider "particles" (but not in the Newtonian sense) to be the basic building blocs, but which have a "quantum bookkeeping" which always turns out to be as if there were a field associated with it . So in the first view, the "particle-like" behaviour is the quantum effect of quantizing a classical field, and in the second view, the "field-like" behaviour is the quantum effect of quantizing relativistically a set of particles. But the end result of the operation is always the same mathematical structure: a quantum field.

One thing is sure: the classical particle, as well as the classical field, are "dead" (which does away with the wave-particle duality, which was a dancing between 2 chairs in order to force the behaviour of a quantum particle into the one of a classical particle, or a classical wave).

So that's why I like the expression "wave-icle"

cheers,
Patrick.

16. Jan 20, 2005

### Kane O'Donnell

That's a bloody good explanation of the history of this area of Physics for the amount of space it took up!

Kane

17. Jan 20, 2005

### Norman

Patrick,

Is Weinberg's view expressed in any of his books on QFT (the 3 volume set)?
Cheers

18. Jan 20, 2005

### vanesch

Staff Emeritus
I think it is in chapter 5 of volume 1. But I didn't really read it all, just skimmed through it. I think that the guy around here who knows this stuff very will is Pat (nrqed).

cheers,
Patrick.

19. Jan 20, 2005

### Norman

Thanks Patrick. I will just wait for it to arrive- I actually ordered it yesterday- only the first volume, that is why I was curious.
Thanks.