Matter & Photon Particle Comparison

1. The problem statement, all variables and given/known data
Compare and contrast a 2.2 eV photonn with a 2.2 eV electron in terms of energy(J), rest mass (Kg) speed (m/s) wavelength (m) and momentum kgm/s.

2. Relevant equations

For Photon
P=E/C
F=E/h
V=fλ
λ= h/P

For Electron
λ=h/mv
m=E/C2
p=h/λ
Ke=1/2mv2

3. The attempt at a solution

Photon
2.2 ev X 1.6x10-19= 3.52 x10 -19 J

P=E/C
P= 3.52 x10 -19 / 3 x 108
P= 1.17 x10 -27

f= E/h
=3.52 x10 -19 /6.63x10-34
F=5.31x1014

v=fλ
v= 3x108 m/s

λ= h/P
=6.63X10-34/1.17X10-27
=5.66X10-7 m

m=? ( Does a photon have a rest mass?) I don't think a photon has a rest mass.

Electron

2.2 eV x1.6x10-19 = 3.52 x 10-19 J

Should rest mass be the standard 9.11 x10-31 kg

Or should I calculate using E=mc2

m= E/C2
m= 3.52 x 10-19 / (3x108)2
m=3.91 x10 -36 kg

( I use 9.11 x10-31 kg as the mass for the rest of the calculations but I can change it if its incorrect and the calculated mass should be used! )

Ek=1/2mv2
3.52 x 10-19=1/2 (9.11x10-31)v2
v= √[(3.52 x 10-19)(2)/9.11x10-31]
v=8.79x105 m/s ( Unsure whether I can use this equation to determine speed)

λ=h/mv
= 6.63x10-34/(9.11X10-31)(8.79X105)
=8.28X10-10 m

p= h/λ
=6.63x10-34/8.28X10-10
=8x10-25 kgm/s

Parts I have highlighted is where I am unsure! Thanks for all the help!

If I have misused any equations ( i.e used matter equations for light or vice versa can you please alert me! )

Recognitions:
Homework Help
 Quote by HarleyM 3. The attempt at a solution Photon 2.2 ev X 1.6x10-19= 3.52 x10 -19 J
Correct. I didn't check your numbers, but make sure you don't round off your physical constants and intermediate results too early so that you have adequate precision for your final answer.

 P=E/C P= 3.52 x10 -19 / 3 x 108 P= 1.17 x10 -27
Correct. You're missing the units though.

 f= E/h =3.52 x10 -19 /6.63x10-34 F=5.31x1014
Why bother? They didn't ask for the frequency.

 v=fλ v= 3x108 m/s
Just quote v = c (then the numerical value as you did).

 λ= h/P =6.63X10-34/1.17X10-27 =5.66X10-7 m
Correct. I didn't check your numerical computation, but make sure you don't have an error in your last few significant digits (because you rounded off the previous answer).

 m=? ( Does a photon have a rest mass?) I don't think a photon has a rest mass.
You're right, photons have no rest mass. Answer is 0.

 Electron 2.2 eV x1.6x10-19 = 3.52 x 10-19 J
Correct.

 Should rest mass be the standard 9.11 x10-31 kg Or should I calculate using E=mc2
No. Rest mass is just the standard constant. It doesn't change.

 m= E/C2 m= 3.52 x 10-19 / (3x108)2 m=3.91 x10 -36 kg
Unnecessary. You are actually calculating the apparent gain in mass due to kinetic energy. Note that this is small relative to the rest mass (error of 4 parts per million or so).

 ( I use 9.11 x10-31 kg as the mass for the rest of the calculations but I can change it if its incorrect and the calculated mass should be used! )
No, use the rest mass.

 Ek=1/2mv2 3.52 x 10-19=1/2 (9.11x10-31)v2 v= √[(3.52 x 10-19)(2)/9.11x10-31] v=8.79x105 m/s ( Unsure whether I can use this equation to determine speed)
You can, since the electron is clearly travelling at speeds significantly less than c. So relativistic effects don't matter. I didn't check your computation, but the principle is right.

 λ=h/mv = 6.63x10-34/(9.11X10-31)(8.79X105) =8.28X10-10 m
Looks right.

 p= h/λ =6.63x10-34/8.28X10-10 =8x10-25 kgm/s
You can just do p = mv, which you calculated as the denominator in the previous part.
 Wow very concise answer, thank you very much WOOO i get physics, its a great feeling

 Tags comparison, electron, energy, particle, photon