Introduction to electromagnetism - Maxwell's equations


by krtica
Tags: electromagnetism, wave
krtica
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#1
Apr23-10, 05:39 PM
P: 50
Q1) The amplitude of an electromagnetic wave is E0 = 471.0 V/m. Find the following values.
(a) Erms
333.047 V/m

(b) Brms
__ nT

(c) the intensity I
__W/m2

(d) the radiation pressure Pr
__nPa


Q2)(a) For a given distance from a radiating electric dipole, at what angle (expressed as θ and measured from the dipole axis) is the intensity equal to 83 percent of the maximum intensity?

(b) At what angle θ is the intensity equal to 3 percent of the maximum intensity?




I'm not sure what the general formulas are.
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berkeman
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#2
Apr23-10, 08:10 PM
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Quote Quote by krtica View Post
Q1) The amplitude of an electromagnetic wave is E0 = 471.0 V/m. Find the following values.
(a) Erms
333.047 V/m

(b) Brms
__ nT

(c) the intensity I
__W/m2

(d) the radiation pressure Pr
__nPa


Q2)(a) For a given distance from a radiating electric dipole, at what angle (expressed as θ and measured from the dipole axis) is the intensity equal to 83 percent of the maximum intensity?

(b) At what angle θ is the intensity equal to 3 percent of the maximum intensity?




I'm not sure what the general formulas are.
Hint for 1b -- the ratio of E/B is determined by the characteristic impedance of the medium that the EM wave is propagating through.

And on question 2, you must have learned some things about dipole antenna radiation patterns, or they would not have asked you that question.
ideasrule
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#3
Apr23-10, 08:10 PM
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Here are the general formulas:

E=Bc
Energy density=1/2*epsilon*E^2
Energy density=1/2*B^2/mu

Dipole formulas: http://en.wikipedia.org/wiki/Dipole_antenna


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