If magnetic forces resist a changing magnetic field, how do antennas radiate EM waves

  • #1
I understand a changing current in a wire gives way to an opposite magnetic field that resists the induced magnetic field, until there is no change in magnetic field, then you're left with a constant induced magnetic field.

So my confusion with the antenna is when an electron rapidly oscillates across the span of the antenna, there would be a rapidly oscillating opposing magnetic response that would nullify the original signal, or at least considerably weaken it.

So how do antenna's operate efficiently?
 

Answers and Replies

  • #2


Nevermind I guess I kind of answered my own question in there. A resisting magnetic force only comes up when the electrons accelerate, as in change direction. Then it moves at a constant speed throughout the span of the antenna so there is no opposing force.
 
  • #3
sophiecentaur
Science Advisor
Gold Member
2020 Award
26,420
5,506


Which "electron" is moving along the antenna? At Radio Frequencies, the electrons actually can be thought of as oscillating by a minute fraction of the diameter of an atom. Just stick to 'current' for your argument.
This induced field is, in fact, there (a reactive element) but there is also a small resistive element which represents Power radiated into space.
 
  • #4
187
0


<<If magnetic forces resist a changing magnetic field, how do antennas radiate EM waves>>

There is resistance, but that does not mean the resistance is complete. When you drive your car, air hitting the windshield and elsewhere provides some resistance, but that does not imply your car cannot go faster than zero miles per hour.

The resistance of the antenna is due to it emitting energy. Energy is leaving the antenna as radiation, and if there were no resistance then total energy would go up rather than being conserved.
 
Last edited:
  • #5


Thank you, i understand it much better now
 

Related Threads on If magnetic forces resist a changing magnetic field, how do antennas radiate EM waves

  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
3
Views
809
Replies
5
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
12
Views
8K
  • Last Post
Replies
10
Views
2K
Replies
3
Views
626
Replies
6
Views
13K
  • Last Post
Replies
7
Views
2K
Top