# Help Needed: Solving Difficult Homework Questions Before Friday Night

• pop

#### pop

I have HW is Difficult for me

if anybody can help me :(

Q1:
1)In a conducting media the wave equation:
$$\Delta$$^2$$E$$=$$\mu$$$$\sigma$$$$dE/dt$$+$$\mu\epsilon$$$$d2E/dt2$$

has solution of the type E(z, t) = E0 exp [ i (kZ –w t)], where
$$\kappa$$^2 = $$\mu\epsilon$$ w2 + i $$\mu\sigma$$ w.
a) Find explicit expressions for real and imaginary parts of $$\kappa$$ .
b)Show that in a good conductor the electric field leads the magnetic field by 45(deg) and find the ratio of their amplitudes. ?

Q2:
A monochromatic plane polarized electromagnetic wave
E(r, t) = E0 sin (k. r – w t) is traveling eastward.
The wave is polarized with E directed vertically up and down alternately. Calculate E, B and the Poynting vector S provided that the amplitude of the electric field strength is 0.05 V/m and the frequency = 6 MHz. Also, find the <S>?

plez I want to the answer. befor friday night

thanx for all

Hi pop, Welcome to PF! As per the forum rules, you need to show some attempt at a solution in order to get assistance here.

Welcome to PF!

Hi pop! Welcome to PF! (try using the X2 tag just above the Reply box )

(also, if you use LaTeX, just put tex and \tex at the start and end of each line; and ∇ is \nabla not \Delta )

Q1:
1)In a conducting media the wave equation:
2E = µ σ dE/dt + µ ε d2E/dt2

has solution of the type E(z, t) = E0 ei (kZ –w t), where
k2 = $$\mu\epsilon$$ w2 + i $$\mu\sigma$$ w.
a) Find explicit expressions for real and imaginary parts of $$\kappa$$ .
b)Show that in a good conductor the electric field leads the magnetic field by 45(deg) and find the ratio of their amplitudes. ?

For 1a), just differentiate … what equations do you get? And that should help you with 1b) gabbagabbahey:

thanx
i read it ____________

tiny-tim

hi
For 1a), just differentiate … what equations do you get? yah I know ...if i do this i will get :
k2 = $$\mu\epsilon$$ w2 + i $$\mu\sigma$$ w.

but i don't need this i need Eq 9.126 in Ch 9
in Griffiths. Electrodynamics 3ed >> sorry i can't write it :)

any way thanks a lot ...i did it

_____________

I still wait to your help in Q2

Q2:
A monochromatic plane polarized electromagnetic wave
E(r, t) = E0 sin (k. r – w t) is traveling eastward.
The wave is polarized with E directed vertically up and down alternately. Calculate E, B and the Poynting vector S provided that the amplitude of the electric field strength is 0.05 V/m and the frequency = 6 MHz. Also, find the <S>?

plez I want to the answer. befor friday night

thanx for all

:)

I still wait to your help in Q2

This forum supports LaTeX, which should make writing vector equations easier for you. For example, a general monochramitic plane wave is given by

$$\vec{E}(\vec{r},t)=\vec{E_0}e^{i(\vec{k}\cdot\vec{r}-\omega t)}$$

...Now, as for your question, I'd start by picking a coordinate system (for example, positive x-direction="East" and "vertical"=positive y-direction) and then write explicitly the polarization unit vector and wave vector and use that to re-write $\vec{E}(\vec{r},t)$.

Then, use Faraday's Law to calculate $\vec{B}(\vec{r},t)$. And finally calculate <S>.

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