If a photon has energy 511 keV its momentum is hv/c :
1.2356 *10^20 hv/3*10^10 = 4.1215 * 10^9 what, gr*cm/s or Kg*m/s?

If a photon has energy 511 keV its momentum is hv/c :
1.2356 *10^20 hv/3*10^10 = 4.1215 * 10^9 what, gr*cm/s or Kg*m/s?
Convert everything to SI units, it makes life much simpler...
I get this a lot at work with students (often research students who should know better). They look up an equation for, say, calculating the composition of an aerosol particle from it's refractive index, and plug the numbers in without thinking and are surprised when they get gibberish. Then you point out that they have used concentration in moles/L instead of kg/m3, their density is in kg/m3 but they've used a mass of sample in grams and a volume in nm3 etc.
Equations only give the right answer if all of the variables are in consistent units. Convert the energy into J, and use c in m/s, you have used an Energy in electron volts and c in cm/s these are not consistent units.
For reference:
1 eV =1.6 x 10^{19} J
1 cm = 0.01 m
Thanks,
is it possible to use the cgs? what is 511keV in cgs?
As long as you are consistent.
1 eV is 1.6021772*10^{12}ergwhat is 511keV in cgs?
Physical Constants and Astronomical Data
so momentum is E/c = 5.34374 * 10^23 gr*cm/s?
I'm not sure where you get that from. I thought you were talking about a 511 keV photon?
Putting "(511000 ev / c) in (cm g) /s" into Google returns: 2.73093002 × 10^{17} (cm g) / s
Then send your calcualtor back for a refund (or press the correct buttons).
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