Homework Statement
A spherical capacitor has internal radius ##a## and external radius ##b##. At time ##t = 0##, the charge of the
capacitor is ##Q_0## Then the two shells are connected by a resistor in the radial direction of resistance ##R##. Find the Poynting vector and the energy...
I am trying to understand why an accelerating charge emits radiation/electromagnetic waves but a uniformly moving one does not. I saw one video on Youtube where it seemed that it was explained by the fact that with a uniformly moving charge the Poynting vector was pointing 'in to the volume' -...
If we have a some wire (length L) with a PD of V from one end to the next and a current I moving along it we can work out the Poynting vector. It's pointing radially inwards and so tells you the energy per unit time per unit area flowing into the the surface of the wire.
What I don't understand...
Homework Statement
I reference problem 9.10 Purcell's Electricity and Magnetism (3rd ed).
A very thin straight wire carries current ##I## from infinity radially inward onto a conducting shell with radius R. Show that the total flux of the Poynting vector away from an imaginary tube of radius...
Hello,
For calculating the mean power at a specific cross section of a waveguide, one can calculate the mean value of the temporal function of Poynting Vector, P(t), where P(t) is the ExHy-EyHx. Note that I am not talking about phasors or a sinusoidal state. If I integrate over the waveguide...
As we know, work done by an outside agency in creating some current ''I" in an inductor 'L' is 1/2LI2. Now this result is derived by quasistatic approximation if I am not wrong. Now, I am assuming that in non quasistatic (real) scenarios, the work done by outside agency would be different(If you...
Homework Statement
An infinitely long cylindrical capacitor with inner radius a and outer radius b carries a free charge per unit length of ##\lambda_{free}##. The region between the plates is filled with a nonmagnetic dielectric of conductivity ##\sigma##. Show that at every point inside the...
A radar antenna transmits 50kW at 10 GHz. Assume transmission is in a narrow beam, 1m^2 in area, and that within the beam, waves are plane waves. The wave is reflected from an aircraft but only 1% of the power propagates i the direction of the antenna. If the airplane is at a distance of 100km...
The basic idea:
I am interested in the possibility of an azimuthally-directed Poynting vector component which drops with the inverse cube of the distance (or as 1/r^3), primarily because it suggests the possibility of emitting field angular momentum, allowing for a uni-directional torque to be...
I have some problems in calculating the flux of Poynting's vector through a surface.
I have that:
S=c/4π⋅H^2⋅n (S: Poynting's vector, n: versor of the direction of the propagation of the em wave)
H=1/cR A'
but: A=(1/cR) d'; A'=(1/cR) d'' ==> H= (1/cR)^2 d''...
To radiate energy, the Poynting vector must not drop faster than with the inverse square of the distance. Under what circumstances can EM angular momentum be emitted to the vacuum of space (i.e. without being recovered via inductive coupling) and yet not lead to energy losses through radiation...
Hi
I have a quesiton about current start signals in a simple circuit such as explained in http://amasci.com/elect/poynt/poynt.html.
Turning on a switch somewhere in the circuit, sphere of influences, i.e. motions of electrons in wire and generation of Poynting vector around the wire, start from...
So I came across the following image (from Wikipedia)
where the electric and magnetic field lines are depicted for a dipole antenna. From the field lines, it is possible to determine the direction of the poynting vector, using the right-hand rule. If all possible combinations of poynting...
1.There is an electric field between ionosphere and ground, also earth's magnetic field is perpendicular to this E field, hence by poynting theorem integrating E x H across the entire surface of earth gives a great deal of energy flowing west to east.
2. |S| = (E X B)/u0 = (150 V/m X...
Hi.
The Poynting vector is a 3-tuple of real or complex numbers (depending on the respective formulation of electrodynamics) times a unit. It may be pictured as an arrow with some length and direction in IR^3 or IC^3. But is it a "vector" in the strict mathematical sense, i.e. an element of a...
Hi people, I studying electromagnetic waves (intermediate) and
I don't understand how the expression for linear momentum of a wave is obtained, if the wave doesn't carry any mass.
In particular, I have to explain why the radiation pressure on a perfect absorber is half that on a perfect...
Homework Statement
I'm having a problem using the fresnel formulae for these two problems below:
1. Using Fresnel formulae and expression for the Poynting vector show that at the interface between two dielectrics in the absence of absorption R+T=1, where R – is reflectivity and T –...
Homework Statement
How do the normal and tangential components of the Poynting vector in matter, S = E x H , behave at an interface between two simple media where no free current flows, but either free charge or polarization charge is present at the interface?
Homework Equations
E1(para) -...
Suppose we have a charge, ##q## and a magnetic dipole moment, ##\vec m##. They don't move, nothing changes with time, in short, a static situation.
Now, we have at least some regions of space where both the electric field, ##\vec E## and the magnetic field, ##\vec B## are non-zero. That means...
Something I have read in Griffith's Electrodynamics is confusing me. In deriving the Poynting vector, he says to suppose that we have some charge and a current configuration which at some time t produces fields E and B. In the next instant, dt, the charges move around. He then asks the question...
Homework Statement
For an electromagnetic wave with an electric field given by
\mathbf{B}=\mathbf{i} E_o cos (kz-\omega t)+ \mathbf{j} E_o sin (\omega t - kz)
where Eo is a constant
Find
(a) its direction of propagation
(b) the magnetic field
(c) Poynting vector
(d) energy density, i.e., the...