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

Direction of electromagnetic field

  • Thread starter palkia
  • Start date
52
2
1. Homework Statement



In this question, it asks for the magnetic field associated with the electromagnetic wave.
2. Homework Equations


3. The Attempt at a Solution

The magnetic field is perpendicular to Electric field but it can be in either x or z direction...how do I choose the direction.I
 

Attachments

52
2
But in my question,why does the wave travel in -x direction
 

haruspex

Science Advisor
Homework Helper
Insights Author
Gold Member
2018 Award
31,955
4,737
But in my question,why does the wave travel in -x direction
That's what the question setter chose.
Note that this might flip the answer compared to the example at the link I posted.
 
52
2
Is it because of kx+wt or is it part of the question?
 

haruspex

Science Advisor
Homework Helper
Insights Author
Gold Member
2018 Award
31,955
4,737
Is it because of kx+wt
Yes, the form kx+wt tells you it is travelling in the -x direction, assuming k and w are positive.
You can figure this out by asking where the wave will move to after time Δt. This is the same as asking what change Δx in x will cancel out the change Δt in t:
sin(kx+kΔx+wt+wΔt)=sin(kx+wt) for all x.
Clearly it is kΔx=-wΔt, so the wave is travelling in the -x direction at speed w/k.
 
52
2
So by shfting by dt of the magnetic or electric field will tell us the direction
 

haruspex

Science Advisor
Homework Helper
Insights Author
Gold Member
2018 Award
31,955
4,737
So by shfting by dt of the magnetic or electric field will tell us the direction
By shifting the time base and considering what corresponding shift in x will keep the wave unchanged. If a positive change in t goes with a positive change in x then the wave is advancing in the +x direction.
 

Related Threads for: Direction of electromagnetic field

Replies
9
Views
2K
Replies
4
Views
1K
  • Last Post
Replies
1
Views
783
  • Last Post
Replies
5
Views
961
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
2
Views
559
  • Last Post
Replies
10
Views
574
  • Last Post
Replies
1
Views
875
Top