if E = hc/lambda
and E= mc^2
a photon with wavelength 546nm.
am I right in saying m = h/(lambda x c)
= 4.05^-36 kg
???
2006-09-21 02:53:46 · 8 answers · asked by benabean87 2 in Science & Mathematics ➔ Physics
No. Totally and completely wrong in fact.
Photons have no mass.
While it might seem that you just used two physical equations to derive a result, you have, in fact, misused E=mc^2.
Through a rigorous mathematical analysis of the special theory of relativity, it can be shown that the energy of a body is given by
E = mc^2 + 0.5mv^2 <-- classical kinetic energy plus the E=mc^2 energy.
IN THE LIMIT OF LOW SPEEDS
The mistake you made is in assuming that you can apply E=mc^2 to something travelling at the speed of light. E=mc^2 is ONLY a low speed approximation, never apply it to a particle with a speed which is a sizeable fraction of the speed of light.
The correct formula to apply if you want to further understand photons is
E^2 = p^2c^2 + m^2c^4
Where m is the rest mass, and p is the momentum.
Given that m = 0 for photons, this will lead you to E=pc
In other words, photons do not have mass, but they DO have momentum (which has also been experimentally proven fact).
Actually, NASA have hopes to use this as a form of propulsion.
EDIT:
Oh, and one more thing; I like to point this out from time to time, after reading the second answer, which alludes to the fact that mass changes with speed. This is a complete misconception about special relativity - it is not the mass of a body that changes with speed, it is, in fact, the definition of speed that changes with speed.
2006-09-21 03:02:30 · answer #1 · answered by ? 3 · 2⤊ 2⤋
You're are only partially right. What you have calculated is the relativitic mass of a photon with wavelength of 546 nm. The REST mass of the photon is still ZERO, since photons are never at rest. And notice that your calculated answer changes with different wavelengths of light.
A better way is to say that light have momentum and kinetic energy.
2006-09-21 04:08:57 · answer #2 · answered by PhysicsDude 7 · 2⤊ 0⤋
I dont know on the subject of the plenty yet a photon is form of a 'packet' of light. whilst an electron is worked up from its floor state, it quickly drops backpedal to the floor state dropping the surplus power in the approach. the surplus power is given off as a photon.
2016-12-12 12:14:59 · answer #3 · answered by Anonymous · 0⤊ 0⤋
a photon has a very small mass
this is proved by the fact that the path of a photon affects the space time around it(in ordinary terms it has a slight affect on gravity)and also gets effected by it
hence it has mass
for all practical purposes the mass is equal to 1/infinity that is very close to zero but not zero itself
2006-09-21 03:06:48 · answer #4 · answered by technitium2310 1 · 0⤊ 2⤋
A photon has momentum but not mass. At least no rest mass.
2006-09-21 02:58:47 · answer #5 · answered by campbelp2002 7 · 2⤊ 2⤋
Yes, you are correct.
2006-09-21 03:25:59 · answer #6 · answered by bruinfan 7 · 0⤊ 1⤋
Hmmmm! I think you need to take a break!!
2006-09-21 03:02:38 · answer #7 · answered by i_b_moog 3 · 0⤊ 3⤋
Ohh, I should guess so ......... Are you thinking of sending one by Royal Mail?
2006-09-21 02:58:38 · answer #8 · answered by prospero 2 · 0⤊ 4⤋