Electromagnetic wave... How is it getting transmitted?

Click For Summary

Discussion Overview

The discussion revolves around the transmission of electromagnetic (EM) waves, focusing on the nature of electric and magnetic fields associated with charges, their propagation, and the concept of energy in relation to EM waves. The scope includes theoretical aspects of electromagnetism and conceptual inquiries regarding energy conservation.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that an EM wave consists of mutually perpendicular electric and magnetic oscillations and questions how oscillations can be transmitted indefinitely given that the electric field diminishes with distance from a charge.
  • Another participant explains that the radiated wave weakens as it propagates, with electric and magnetic fields decreasing as ##\frac{1}{R}##, leading to power density falling off as ##\frac{1}{R^2}##, where ##R## is the distance from the oscillating charge.
  • A follow-up question is raised about whether an EM wave can be considered a form of perpetual energy, with one participant expressing an instinctive belief that this cannot be true but lacking a clear rationale.
  • One participant asserts that the EM field from any object extends to infinity, suggesting that the electric field of the sun reaches the distances where its light can travel.

Areas of Agreement / Disagreement

Participants express differing views on the nature of EM waves and energy, with some questioning the concept of perpetual energy while others clarify aspects of energy conservation and field propagation. The discussion remains unresolved regarding the implications of these concepts.

Contextual Notes

There are limitations in the discussion regarding the assumptions about field strength and the nature of energy transfer in EM waves, as well as the implications of the term "perpetual energy." These aspects are not fully explored or defined.

jijopaul
Messages
5
Reaction score
0
I've heard that em wave consists of mutually perpendicular electric & magnetic oscillations.

Imagine that I've a unit charge at any point in space. Associated with this charge, there exists an electric field which diminishes with distance from the charge. If we set forth an oscillation in this field, it can get transmitted. But since the field strength is getting diminished wrt distance, How can the oscillation get transmitted indefinitely?
 
Physics news on Phys.org
The radiated wave does get weaker as it propagates away from its source. For your case, the electric and magnetic fields both off as ##\frac{1}{R}##, so the power density falls off as ##\frac{1}{R^2}##. Here ##R## is the distance from your oscillating charge to the point at which you are observing the wave.

jason
 
As a follow up question, can an EM wave be considered a form of perpetual energy? I 'know' instinctively that this cannot be true, but I don't know why.
 
jasonRF said:
The radiated wave does get weaker as it propagates away from its source. For your case, the electric and magnetic fields both off as ##\frac{1}{R}##, so the power density falls off as ##\frac{1}{R^2}##. Here ##R## is the distance from your oscillating charge to the point at which you are observing the wave.

jason
For how much length the electric field of a unit charge exist?
Light reaches from sun to Earth after traveling that much distance. You mean to say that the electric field of the sun extends up to the distances where its light can reach?
 
Burnerjack said:
As a follow up question, can an EM wave be considered a form of perpetual energy? I 'know' instinctively that this cannot be true, but I don't know why.

Sure. Until the EM wave interacts with something, it will always have some amount of energy. The phrase 'perpetual energy' is mostly meaningless though. Energy is conserved, so it never disappears, but just gets transferred around and changes form. This is in contrast to a 'Perpetual Motion Machine'. A machine is basically a device that moves energy around. Adding 'perpetual motion' implies that the machine can run forever, performing work without expending energy. This is impossible.

jijopaul said:
For how much length the electric field of a unit charge exist?
Light reaches from sun to Earth after traveling that much distance. You mean to say that the electric field of the sun extends up to the distances where its light can reach?

The EM field from any object extends to infinity.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 65 ·
3
Replies
65
Views
6K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K