• Support PF! Buy your school textbooks, materials and every day products Here!

Lorentz Law

  • Thread starter dpeagler
  • Start date
  • #1
34
0

Homework Statement



An electron has a velocity of 1.2 * 10^4 m/s ( in the positive x direction ), and an acceleration of 2 * 10 ^ 12 m/s^2 ( in the positive z direction ) in a uniform electric and magnetic field. If the electric field has a magnitude of 20 N/C ( in the positive z direction), what can you determind about the magnetic field in the region? what can you not determine?

Homework Equations



F = qE + qv x B

The Attempt at a Solution



I need the force quantity to figure out the problem, but am lost besides this. Can someone offer a little help. Thanks.
 

Answers and Replies

  • #2
Pengwuino
Gold Member
4,989
15
You are given the acceleration and the mass of an electron is something you can easily look up.
 
  • #3
34
0
Ok I was thinking I was going to be using Newton's second law, but wan't sure. I have the answers to the problem and for the x- vector it says it can be any negative value, can anyone explain why this is?
 
  • #4
Pengwuino
Gold Member
4,989
15
Well you do need to use Newton's 2nd law since F = ma to use the left hand side of your equation. As far as the x-direction of the magnetic field is concerned, what happens when you cross a velocity, that is in the x-direction, with a field in the x-direction? Matter of fact, what happens when you cross any 2 parallel directions together?
 
  • #5
34
0
It would be zero not any negative value correct?

Thanks for all of the help.
 
  • #6
Pengwuino
Gold Member
4,989
15
Yes, any x-component, negative or positive, crossed into the velocity would give 0 here.
 

Related Threads on Lorentz Law

  • Last Post
Replies
3
Views
857
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
6
Views
11K
  • Last Post
Replies
0
Views
791
Replies
4
Views
823
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
3
Views
1K
Replies
19
Views
3K
Replies
9
Views
2K
Replies
3
Views
3K
Top