Solve Media Homework: Relative Permittivity of Non-dissipative Medium

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Discussion Overview

The discussion revolves around a homework problem involving the calculation of the relative permittivity of a non-dissipative medium based on phase measurements of a uniform plane wave. Participants explore the relationships between phase angles, wave numbers, and permittivity in the context of electromagnetic wave propagation.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • The initial problem statement includes relevant equations for wave propagation, such as the relationship between wave number, angular frequency, permeability, and permittivity.
  • One participant expresses confusion about how to derive the relative permittivity from the given phase measurements at different positions.
  • Another participant clarifies that the medium is non-dissipative, challenging the initial categorization of the topic as "conducting" media.
  • There is a discussion about equating phase differences to wave number differences, with some participants questioning the need for multiple permittivity values.
  • One participant suggests that the other permittivity might simply be the permittivity of free space (e0), indicating a potential misunderstanding of the problem setup.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the interpretation of the problem, particularly regarding the necessity of finding multiple permittivity values. Some participants assert that there should only be one permittivity, while others explore the implications of having two phase measurements.

Contextual Notes

There are unresolved assumptions regarding the definitions of permittivity in the context of the problem, as well as the implications of the phase measurements on the calculations. The discussion reflects uncertainty about the relationships between the variables involved.

Who May Find This Useful

This discussion may be useful for students studying electromagnetic theory, particularly those working on problems related to wave propagation in different media and the mathematical relationships governing these phenomena.

Maat
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Homework Statement



A uniform plane wave propagates in a non-dissipative medium in the positive z direction. The frequency of the wave is 20 MHz. A probe located at z = 0 measures the phase of the wave to be 98 degrees. An identical probe located at z = 2 m measures the phase to be -15 degrees. What is the relative permittivity (e/e0) of the medium.

Homework Equations



k = w*sqrt(u*e)

w = 2*pi*f

wt - kz = a constant

w is angle velocity, u is permeability, e is permittivity

The Attempt at a Solution



wt = phase angle

Phase angle = kz

K2 = -15/2 = -7.5

w = 2*pi*(20*10^6)

K2 = w*sqrt(u*e), solve for e (e2)

e2 = 2.83 * 10^-9 F/m

Now I'm stuck on how to get the other e since z = 0. I think this problem should be easy, but I'm not seeing something.
 
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Why is your topic "conducting" media? It's not conducting. Conducting media dissipate. Yours is stated to be "non-dissipative".

Maat said:

Homework Statement



k = w*sqrt(u*e)
Phase angle = kz
w = 2*pi*(20*10^6)

All correct. (Some of the other stuff you posted wasn't, but never mind).

So how about equating delta degrees to delta kz?
 
If I equated the deltas, how would I get two different e's? My thought was to get two different k's and from that find the two e's to compare.
 
Maat said:
If I equated the deltas, how would I get two different e's? My thought was to get two different k's and from that find the two e's to compare.

Why are you looking for two different epsilons? there is only one epsilon.
There is also only one k.
There are however two z's and two phase angles.
 
Ah is that because the other epsilon is just e0?
 
Ok I see now. Thank you very much.
 

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