Homework Statement
When deriving the intensity of an electromagnetic wave in my textbook, there was a part I didn't quite get.
It's how I = Watts/m^2 becomes I= u c
My textbook gave an example of a electromagnetic wave through a cylinder, with cross-section area A. In 1 second it would...
Ah now I get it. I guess what confused me was that it was called an approximation, but as you pointed out the small x wasn't going towards zero. Thank you both of you ^^
Homework Statement
I just stumbled upon an approximation I don't get where comes from
Homework Equations
F(x+dx) -F(x) = dF/dx dx
The Attempt at a Solution
My textbook just stated it out of nothing, so I have no idea where to start.
hmm thanks. I might have gotten it (tried surfing around the web)
I do get this though:
\oint\limits_S \vec{B} \cdot d \vec{A} = 0
So that helped a lot
But from my understanding of what divergence is, I don't quite get it when it is in the form: div B = 0
(with my understanding of...
When you say div B = 0 mean that magnetic field lines only forms closed loops, is that in the moment a magnetic field begins and end (if that were to happen) there would be a change in what goes in in relation to what goes out and thus div B wouldn't be 0? That at least makes sense to me.
The B...
The divergence of a vector field tells us how many field lines goes into a volume element in relation to how many goes out.
So if div B = 0 there should be the same amount of magnetic field lines going into a volume element as are going out of it right?
But the Biot-Savart equations tells...
Homework Statement
http://img809.imageshack.us/img809/5676/unavngivetk.png
Additional table info:
The molarmass ##M_{air}## is ##29 * 10^{-3} g/mol = 29*\frac{10^{-3}}{1000} kg/mol##
The mass density ## \rho_{air} ## is ##1.3 kg/m^{3}##
The dielectric constant ## K_{air}## is 1.00059
My...
Homework Statement
I'm having some troubles with my calculus. I can't get from the first step to the second step in the example below:
Homework Equations
http://img853.imageshack.us/img853/4350/unavngivetpn.png
The Attempt at a Solution
\int_{-L/2}^{L/2} [R^2 + (Z-Z_0)^2]^{1/2} -...
Homework Statement
http://img842.imageshack.us/img842/2816/unavngivettz.png
My problem is that I'm confused about a hint I was given in this problem. I usually use the law of cosine to find the length of \vec{r}-\vec{r'} in sphere problems. But the hint I have says that I should make it...
Oh there seems to be one more thing I don't quite get. This whole problem was how to calculate the potential of a hollow sphere
With the equation like this:
\phi = \frac{Q}{8 \pi \epsilon_0} \frac{|R + Z| - |R - Z|}{R Z}
It seems that you are able to remove the absolute values when specified...