Energy of a massless particle

  • Thread starter khkwang
  • Start date
  • #1
60
0

Homework Statement



Show that if mass = 0, then E=pc and u=c.

Homework Equations



E^2 = (pc)^2 + (mc^2)^2
B = u/c = pc/E

The Attempt at a Solution



I understand that if m=0, then E^2=(pc)^2 => E=pc.

But isn't p = Ymu? then:
E^2 = (Ymuc)^2 + (mc^2)^2

Plugging in m=0 sets E=0...

It seems strange to me that we can remove (mc^2)^2 from the equation due to m=0, but we can leave (Ymuc)^2 in.

I'm thinking that this definition of p is not the same as Ymu?

EDIT: wait... Y would equal infinity. Which multiplied with 0 makes ??? I'm just plain confused now.
 

Answers and Replies

  • #2
kuruman
Science Advisor
Homework Helper
Insights Author
Gold Member
10,725
3,736
p = γmu does not apply to massless particles.
 
  • #3
60
0
Ahhh simple as that lol, thanks.
 

Related Threads on Energy of a massless particle

  • Last Post
Replies
2
Views
2K
Replies
19
Views
3K
Replies
8
Views
9K
Replies
3
Views
3K
Replies
3
Views
2K
  • Last Post
Replies
4
Views
1K
Replies
5
Views
1K
  • Last Post
Replies
1
Views
841
  • Last Post
Replies
14
Views
8K
  • Last Post
Replies
14
Views
10K
Top