5th semester files

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clear all;
k = 9e9;
q1 = 1.0e-6;
q2 = -1.0e-6;
ax = 1.0;
ay = 0;
bx = -1.0;
by = 0;
[X, Y] = meshgrid(-2:0.9:2,-2:0.9:2);
V = 1./sqrt((X - ax).^2 + (Y-ay).^2 ) * k * q1 + 1./sqrt((X-bx).^2 + (Y-by).^2) * k * q2;
surfc(X, Y, V);
[Ex, Ey] = gradient(-V, 0.2, 0.2);
figure
contour(X, Y, V);
hold on;
quiver(X, Y, Ex, Ey);

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clear;
clf;
N = 50;
L = 20.0;
h = L/N;
c = 1;
tau = h/c;
nstep = 50;
coef = c * tau / (2*h);
sig=0.1; % width of the pulse
z = ((1:N) - 1/2)*h - L/2; % value of z at time 0
phi = (sech(z / (2 * sig^2))).^2; % wave shape
phiset = zeros(nstep, N);
x = z;
t = 0:tau:(nstep - 1) * tau;
[xx, tt] = meshgrid(x, t);
for ist = 1:nstep
phiset(ist,:) = phi;
for k = 1:N
if ( k ~= 1 ) && ( k ~= N )
phinew(k) = (0.5-coef)*phi(k+1) + (0.5+coef)*phi(k-1);
else
phinew(1) = (0.5-coef)*phi(2) + (0.5+coef)*phi(N);
phinew(N) = (0.5-coef)*phi(1) + (0.5+coef)*phi(N-1);
end
end
phi = phinew;
end
surf(xx, tt, phiset);

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# Homework 1 - Aidan Sharpe
## 1.
If $\vec{A} = 4\hat{x} + 4\hat{y} - 2\hat{z}$ and $\vec{B} = 3\hat{x} - 1.5\hat{y} + \hat{z}$, find the acute angle between $\vec{A}$ and $\vec{B}$.
Definition of dot product:
$$\vec{A} \cdot \vec{B} = (A_x B_x)+(A_y B_y) + (A_z B_z) =\lVert \vec{A} \rVert \lVert \vec{B} \rVert \cos(\varphi)$$
Solve the dot product:
$$\vec{A} \cdot \vec{B} = (4 \cdot 3) + (4 \cdot (-1.5)) + ((-2) \cdot 1) = 4$$
Magnitudes of the vectors:
$$\lVert \vec{A} \rVert = \sqrt{4^2 + 4^2 + (-2)^2} = \sqrt{36} = 6$$
$$\lVert \vec{B} \rVert = \sqrt{3^2 + \left(-\frac{3}{2}\right)^2 + 1^2} = \sqrt{\frac{49}{4}} = \frac{7}{2}$$
By the definition of the dot product:
$$4 = 6 \cdot \frac{7}{2} \cos(\varphi)$$
$$\therefore \cos(\varphi) = \frac{4}{21}$$
$$\therefore \varphi = \arccos\left(\frac{4}{21}\right) = 1.379 = 79.02^\circ$$
## 2
If $\vec{A} = \frac{10}{\rho}\hat{\rho} + 5\hat{\varphi} + 2\hat{z}$ and $\vec{B} = 5\hat{\rho} + \cos(\varphi)\hat{\varphi} + \rho\hat{z}$, find (a) $\vec{A} \cdot \vec{B}$ and (b) $\vec{A} \times \vec{B}$ at $x=1$, $y=1$, $z=1$.
Convert from cartesian to cylidrical:
$$\rho = \sqrt{x^2 + y^2} = \sqrt{2}$$
$$\varphi = \arctan\left(\frac{y}{x}\right) = \frac{\pi}{4}$$
$$z = z = 1$$
Find $\vec{A}$ and $\vec{B}$ at $x=1$, $y=1$, $z=1$:
$$\vec{A} = \frac{10}{\sqrt{2}}\hat{\rho}+5\hat{\varphi}+2\hat{z} = 5\sqrt{2}\hat{\rho}+5\hat{\varphi}+2\hat{z}$$
$$\vec{B} = 5\hat{\rho}+\cos\left(\frac{\pi}{4}\right)\hat{\varphi}+\sqrt{2}\hat{z}=5\hat{\rho}+\frac{\sqrt{2}}{2}\hat{\varphi}+\sqrt{2}\hat{z}$$
### a) Find $\vec{A} \cdot \vec{B}$
$$\vec{A} \cdot \vec{B} = \left(5\sqrt{2} \cdot 5\right) + \left(5 \cdot \frac{\sqrt{2}}{2}\right) + \left(2 \cdot \sqrt{2}\right) = \frac{59\sqrt{2}}{2}$$
### b) Find $\vec{A} \times \vec{B}$
$$\vec{A} \times \vec{B} = \begin{vmatrix} \hat{\rho} & \hat{\varphi} & \hat{z} \\ 5\sqrt{2} & 5 & 2 \\ 5 & \frac{\sqrt{2}}{2} & \sqrt{2} \end{vmatrix} = 4\sqrt{2}\hat{\rho} - 20\hat{z}$$
## 3
Two point charges have mass $0.2$g. Two insulating threads of length $1$m are used to suspend the charges from a common point. The gravitational force is $980 \times 10^{-5}\text{N/g}$.
Define $\varphi$ as the angle between the threads, $\alpha$ as half of that angle, and $\beta$ as $\frac{\pi}{2} - \alpha$. This way, $\alpha$ and $\beta$ make a right triangle with the leg adjacent to $\alpha$ making a perpendicular bisector of the distance between the charges, $r$.
Find the distance, $r$:
$$\frac{r}{2} = (1\text{m})\cos(\beta)$$
$$\therefore r = 2\cos(\beta)$$
By Coulomb's Law, the electric field force on each charge, $\vec{F}_e$, is:
$$\vec{F}_e = \frac{q^2}{4\pi\varepsilon_0 r^2}\hat{x}$$
Pluggin in for $r$,
$$\vec{F}_e = \frac{q^2}{16\pi\varepsilon_0\cos^2(\beta)}\hat{x}$$
The force due to gravity on each charge, $\vec{F}_g$, is:
$$\vec{F}_g = 0.2 \cdot 980\times 10^{-5} = 0.00196(-\hat{y})\text{N}$$
Assuming static equilibrium:
$$\sum F_x = 0 = F_{e_x} + F_{T_x} + F_{g_x}$$
$$\sum F_y = 0 = F_{e_y} + F_{T_y} + F_{g_y}$$
Where:
$F_{T_x}$ is the x-component of the force due to tension in each thread, $F_T$.
$F_{T_y}$ is the y-component of $F_T$.
Since $F_g$ only acts in the $\hat{y}$ direction, and $F_e$ only acts in the $\hat{x}$ direction:
$$F_{e_x} + F_{T_x} = 0$$
$$F_{T_y} + F_{g_y} = 0$$
Define the components of the tension force $F_T$:
$$F_{T_x} = F_T\cos\left(\frac{\pi}{2} + \alpha\right) = -F_T\cos(\beta)$$
$$F_{T_y} = F_T\sin\left(\frac{\pi}{2} + \alpha\right) = F_T\sin(\beta)$$
Solve for $F_T$ using equilibrium in the $\hat{y}$ direction:
$$F_T\sin(\beta) - 0.00196 = 0$$
$$\therefore F_T = \frac{0.00196}{\sin(\beta)}$$
Plug in $F_T$ to solve equilibrium in the $\hat{x}$ direction:
$$F_e + \left( \frac{0.00196}{\sin(\beta)} \right)(-\cos(\beta)) = 0$$
$$\therefore F_e = 0.00196 \cot(\beta)$$
### a) When $\varphi = 45^\circ$, solve for the charge, $q$:
Since $\varphi = \frac{\pi}{4}$, $\alpha = \frac{\pi}{8}$, and $\beta = \frac{3\pi}{8}$.
Known:
$$F_e = \frac{q^2}{16\pi\varepsilon_0\cos^2(\beta)}$$
$$F_e = 0.00196\frac{\cos(\beta)}{\sin(\beta)}$$
Set equal:
$$\frac{q^2}{16\pi\varepsilon_0\cos^2(\beta)} = 0.00196\cot(\beta)$$
$$\therefore q^2 = 16\pi\varepsilon_0\frac{\cos^3(\beta)}{\sin(\beta)}$$
Plug in for $\beta$ and solve for $q$:
$$q = \pm \sqrt{16\pi\varepsilon_0(0.00196)\frac{\cos^3\left(\frac{3\pi}{8}\right)}{\sin\left(\frac{3\pi}{8}\right)}} = \pm 2.300\times10^{-7}\text{C}$$
### b) When $q=0.5\mu\text{C}$, solve for the angle, $\varphi$:
Known:
$$F_e = \frac{q^2}{16\pi\varepsilon_0\cos^2(\beta)}$$
$$F_e = 0.00196\frac{\cos(\beta)}{\sin(\beta)}$$
Set equal:
$$\frac{q^2}{16\pi\varepsilon_0\cos^2(\beta)} = 0.00196\cot(\beta)$$
Plug in for $q$:
$$\frac{(0.5\times 10^{-6})^2}{16\pi\varepsilon_0(0.00196)} = \frac{\cos^3(\beta)}{\sin(\beta)}$$
$$\therefore \frac{\cos^3(\beta)}{\sin(\beta)} = 0.287$$
$$\therefore \beta = 0.915$$
Using $\beta$ to solve for $\varphi$:
$$\alpha = \frac{\pi}{2} - \beta = 0.656$$
$$\varphi = 2\alpha = 1.314 = 75.257^\circ$$
## 4
The magnetic field, $\vec{B} = B_0(\hat{x} + 2\hat{y} - 4\hat{z})$ exists at a point. Find the electric field at that point if the force experienced by a test charge with velocity, $\vec{v} = v_0(3\hat{x} - \hat{y} + 2\hat{z})$ is $0$.
Lorentz Force Law:
$$\vec{F} = q\vec{E} + q\vec{v} \times \vec{B}$$
Since $\vec{F}$ is $0$:
$$0 = q\vec{E} + q\vec{v} \times \vec{B}$$
$$\therefore q\vec{E} = -q\vec{v} \times \vec{B}$$
$$\therefore \vec{E} = -\vec{v} \times \vec{B}$$
By the definition of the cross product:
$$-\vec{v} \times \vec{B} = \vec{B} \times \vec{v}$$
In terms of $\vec{E}$:
$$\vec{E} = \vec{B} \times \vec{v} = \begin{vmatrix} \hat{x} & \hat{y} & \hat{z} \\ 1 & 2 & -4 \\ 3 & -1 & 2 \end{vmatrix} = -14\hat{y} - 7\hat{z}$$
## 5
A circular loop with radius, $a$, exists in the x-y plane. If the loop is uniformly charged and has total charge, $Q$, determine the $\vec{E}$-field intensity at some point along the axis normal to the loop.
By Coulomb's Law:
$$\vec{E} = \int \frac{dq}{4\pi\varepsilon_0 r^2}\hat{r}$$
Calling the distance along the normal axis $z$:
$$r^2 = a^2 + z^2$$
Along a uniformly charged line, the charge, $dq$, at any given point is given by the equation:
$$dq = \lambda dl$$
Where:
$\lambda$ is the linear charge density
The linear charge density, $\lambda$ is defined as:
$$\lambda = \frac{Q}{L}$$
Where:
$Q$ is the total charge
$L$ is the total length
For a circular loop with radius, $a$, and total charge, $Q$:
$$\lambda = \frac{Q}{2\pi a}$$
$$dl = a d\varphi$$
$$\therefore dq = \frac{Qd\varphi}{2\pi}$$
Plugging into Coulomb's Law:
$$\vec{E} = \int\limits_{0}^{2\pi} \frac{Qd\varphi}{8\pi^2\varepsilon_0(a^2 + z^2)} \hat{r}$$
$$\therefore \vec{E} = \frac{Q}{8\pi^2\varepsilon_0(a^2 + z^2)} \int\limits_{0}^{2\pi}\hat{r}d\varphi$$
Find $\hat{r}$ in terms of $\hat{x}$, $\hat{y}$, and $\hat{z}$:
$$\hat{r} = \frac{\vec{a} + \vec{z}}{\sqrt{a^2 + z^2}}$$
$$\vec{z} = z\hat{z}$$
$$\vec{a} = a\cos{\varphi}\hat{x} + a\sin{\varphi}\hat{y}$$
Back to Coulomb's Law:
$$\vec{E} = \frac{Q}{8\pi^2\varepsilon_0(a^2 + z^2)^{(3/2)}} \int\limits_{0}^{2\pi} (a\cos(\varphi)\hat{x} + a\sin(\varphi)\hat{y} + z\hat{z})d\varphi$$
By components:
$$E_x = \frac{aQ}{8\pi^2\varepsilon_0(a^2 + z^2)^{3/2}} \int\limits_{0}^{2\pi} \cos(\varphi)d\varphi = 0$$
$$E_y = \frac{aQ}{8\pi^2\varepsilon_0(a^2 + z^2)^{3/2}} \int\limits_{0}^{2\pi} \sin(\varphi)d\varphi = 0$$
$$E_z = \frac{zQ}{8\pi^2\varepsilon_0(a^2 + z^2)^{3/2}} \int\limits_{0}^{2\pi} d\varphi = \frac{zQ}{4\pi\varepsilon_0(a^2 + z^2)^{3/2}}$$
Recombining:
$$\vec{E} = \frac{zQ}{4\pi\varepsilon_0(a^2 + z^2)^{3/2}}\hat{z}$$
## 6
Consider a circular ring in the x-y plane with inner radius, $a$, outer radius, $b$, and uniform charge density, $\rho_s$. Find an expression for the $\vec{E}$-field at a point at distance, $z$, along the axis normal to the ring.
By Coulomb's Law:
$$d\vec{E} = \frac{dq}{4\pi\varepsilon_0 r^2}\hat{r}$$
Calling the radial distance, $\rho$:
$$r^2 = \rho^2 + z^2$$
For surface charge densities:
$$dq = \rho_s ds$$
In cylindrical coordinates:
$$ds = \rho d\rho d\varphi$$
Plugging into Coulomb's Law:
$$\vec{E} = \iint \frac{\rho_s \rho}{4\pi\varepsilon_0(\rho^2 + z^2)}\hat{r}d\rho d\varphi$$
$\hat{r}$ is defined as:
$$\hat{r} = \frac{\vec{\rho} + \vec{z}}{\sqrt{\rho^2 + z^2}}$$
Where:
$\vec{z} = z\hat{z}$
$\vec{\rho} = \rho\cos(\varphi)\hat{x} + \rho\sin(\varphi)\hat{y}$
Splitting $\hat{r}$ by components:
$$\hat{r} = \frac{\rho\cos(\varphi)\hat{x} + \rho\sin(\varphi)\hat{y} + z\hat{z}}{\sqrt{\rho^2 + z^2}}$$
Back to Coulomb's Law:
$$\vec{E} = \frac{\rho_s}{4\pi\varepsilon_0}\int\limits_{0}^{2\pi}\int\limits_{a}^{b} \frac{\rho^2\cos(\varphi)\hat{x} + \rho^2\sin(\varphi)\hat{y} + \rho z\hat{z}}{(\rho^2 + z^2)^{3/2}} d\rho d\varphi$$
By components:
$$E_x = \frac{\rho_s}{4\pi\varepsilon_0}\int\limits_{0}^{2\pi}\int\limits_{a}^{b} \frac{\rho^2\cos(\varphi)}{(\rho^2 + z^2)^{3/2}} d\rho d\varphi = 0$$
$$E_y = \frac{\rho_s}{4\pi\varepsilon_0}\int\limits_{0}^{2\pi}\int\limits_{a}^{b} \frac{\rho^2\sin(\varphi)}{(\rho^2 + z^2)^{3/2}} d\rho d\varphi = 0$$
$$E_z = \frac{\rho_s}{4\pi\varepsilon_0}\int\limits_{0}^{2\pi}\int\limits_{a}^{b} \frac{\rho z}{(\rho^2 + z^2)^{3/2}} d\rho d\varphi = \frac{\rho_s z}{2\varepsilon_0} \left(\frac{1}{\sqrt{z^2 + a^2}} - \frac{1}{\sqrt{z^2 + b^2}}\right)$$
Recombining:
$$\vec{E} = \frac{\rho_s z}{2 \varepsilon_0} \left( \frac{1}{\sqrt{z^2 + a^2}} - \frac{1}{\sqrt{z^2 + b^2}} \right) \hat{z}$$
## 7
Consider two concentric cylindrical surfaces. The inner having radius, $a$, and charge density $\rho_s$, and the outer having radius, $b$, and charge density $-\rho_s$.
By Gauss's Law:
$$\Phi_E = \frac{Q_{enc}}{\varepsilon_0} = \oint_S \vec{E} \cdot d\vec{A}$$
The $\vec{E}$-field for a cylindrical surface with radius, $\rho$, and length, $l$, is given by the equation:
$$2\pi\rho l E = \frac{Q_{enc}}{\varepsilon_0}$$
### a) For $\rho < a$:
$$Q_{enc} = 0$$
$$\therefore E = 0$$
### b) For $a < \rho < b$:
$$Q_{enc} = 2\pi a l\rho_s$$
Where:
$l$ is the length of the section of the cylender.
$$2\pi\rho lE = \frac{2\pi a l \rho_s}{\varepsilon_0}$$
$$\therefore E = \frac{a\rho_s}{\rho \varepsilon_0}$$
### c) For $\rho > b$:
$$Q_{enc} = 2\pi l\rho_s(a-b)$$
$$2\pi \rho l E = \frac{2\pi l \rho_s(a-b)}{\varepsilon_0}$$
$$\therefore E = \frac{\rho_s (a-b)}{\rho \varepsilon_0}$$
## 8
Consider an infinite slab of thickness, $d$, centered on the origin ($x=0$, $y=0$, $z=0$).
By Gauss's Law:
$$\Phi_E = \frac{Q_{enc}}{\varepsilon_0} = \oint_S \vec{E} \cdot d\vec{A}$$
### a) Find the strength of the electric field inside the slab ($\lvert z \rvert < d/2$):
$$Q_{enc} = \rho_v lwh$$
$$\oint_S \vec{E} \cdot d\vec{A} = E(2lw + 2lh + 2wh)$$
$$E = \frac{\rho_v lwh}{2\varepsilon_0(lw + lh + wh)}$$
Where:
$l$ is the size of the x dimension of a Gaussian rectangular prism centered on the origin,
$w$ is the size of the y dimension of that rectangular prism,
$h$ is the size of the z dimension of that rectangular prism
### b) Find the strength of the electric field inside the slab ($\lvert z \rvert > d/2$):
$$Q_{enc} = \frac{\rho_v lwd}{2}$$
$$\oint_S \vec{E} \cdot d\vec{A} = E(2lw + 2lh + 2wh)$$
$$E = \frac{\rho_v lwd}{4\varepsilon_0 (lw + lh + wh)}$$
Where:
$l$ is the size of the x dimension of a Gaussian rectangular prism centered on the origin,
$w$ is the size of the y dimension of that rectangular prism,
$h$ is the size of the z dimension of that rectangular prism

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# Homework 2 - Aidan Sharpe
## 1
Consider a long cylindrical wire of radius, $a$, carrying a current $I = I_0 \cos(\omega t)\hat{z}$.
### a)
Write an expression for the magnetic field strength, $B$, outside the wire ($\rho > a$):
By Ampere's Law:
$$\int \vec{B} \cdot d\vec{l} = \mu_0 I_{enc}$$
For a closed loop of radius, $\rho$:
$$\int \vec{B} \cdot d\vec{l} = B(2\pi\rho)$$
$$\therefore B(2\pi\rho) = \mu_0 I_{enc}$$
Since ($\rho > a$):
$$I_{enc} = I = I_0 \cos(\omega t)$$
Recombining:
$$B(2\pi\rho) = \mu_0 I_0 \cos(\omega t)$$
$$\therefore B = {\mu_0 I_0 \cos(\omega t) \over 2\pi\rho} \text{[T]}$$
### b)
Consider a rectangular loop a distance, $d$, from the wire with sidelengths $\alpha$ in the $\hat{x}$ direction, and $\beta$ in the $\hat{z}$ direction.
#### i)
Calculate the magnetic flux, $\Phi_B$, through the loop.
By Gauss's Law for magnetism:
$$\Phi_B = \iint \vec{B} \cdot d\vec{s}$$
Since the $\beta$ does not vary:
$$\Phi_B = \beta \int\limits_{d}^{d+\alpha} {\mu_0 I_0 \cos(\omega t) \over 2\pi\rho} d\rho$$
Taking out constants:
$$\Phi_B = {\beta \mu_0 I_0 \cos(\omega t) \over 2 \pi} \int\limits_d^{d+\alpha} {1 \over \rho}d\rho$$
Evaluate:
$$\Phi_B = {\beta \mu_0 I_0 \cos(\omega t) \over 2\pi} \ln\left( {\lvert d + \alpha \rvert \over \lvert d \rvert} \right) \text{[Vs]}$$
#### ii)
Find the induced EMF, $\cal{E}$:
$$\mathcal{E} = -{d \over dt}\Phi_B$$
Plug in:
$$\mathcal{E} = -{d \over dt} {\beta \mu_0 I_0 \cos(\omega t) \over 2\pi} \ln\left({\lvert d + \alpha \rvert \over \lvert d \rvert}\right)$$
Evaluate:
$$\mathcal{E} = {\beta \mu_0 I_0 \sin(\omega t) \over 2\pi} \ln\left({\lvert d + \alpha \rvert \over \lvert d \rvert}\right) \text{[V]}$$
## 2
A quarter circle loop of wire with inner radius, $a$, and outer radius, $b$, has current, $I$. Find the magnetic field strength at the center of the circle.
By superposition:
$$B = B_1 + B_2 + B_3 + B_4$$
By Ampere's law:
$$\int \vec{B_1} \cdot d\vec{l} = \mu_0 I_{enc_1}$$
$$\int \vec{B_2} \cdot d\vec{l} = \mu_0 I_{enc_2}$$
$$\int \vec{B_3} \cdot d\vec{l} = \mu_0 I_{enc_3}$$
$$\int \vec{B_4} \cdot d\vec{l} = \mu_0 I_{enc_4}$$
Since the current in the first and third segments are either parallel or antiparallel:
$$I_{enc_1} = 0$$
$$I_{enc_3} = 0$$
Since all of $I$ is enclosed in a loop from either segment two or four:
$$I_{enc_2} = I_{enc_4} = I$$
Back to Ampere's Law:
$$\int \vec{B_1} \cdot d\vec{l} = 0 \therefore B_1 = 0$$
$$\int \vec{B_2} \cdot d\vec{l} = \mu_0 I$$
$$\int \vec{B_3} \cdot d\vec{l} = 0 \therefore B_2 = 0$$
$$\int \vec{B_4} \cdot d\vec{l} = \mu_0 I$$
Determining $d\vec{l}$ for segments two and four:
$$\int \vec{B_2} \cdot \vec{a}d\varphi = \mu_0 I$$
$$\int \vec{B_4} \cdot \vec{b}d\varphi = \mu_0 I$$
Determining the bounds:
$$\int\limits_0^{\pi \over 2} \vec{B_2} \cdot \vec{a} d\varphi = \mu_0 I$$
$$\int\limits^0_{\pi \over 2} \vec{B_4} \cdot \vec{b} d\varphi = \mu_0 I$$
Evaluate:
$$B_2 \left({\pi a \over 2}\right) = \mu_0 I$$
$$B_4 \left({-\pi b \over 2}\right) = \mu_0 I$$
Solve for $B$:
$$B_2 = {2 \mu_0 I \over \pi a}$$
$$B_4 = -{2 \mu_0 I \over \pi b}$$
$$B = {2 \mu_0 I \over \pi a} - {2 \mu_0 I \over \pi b} = {2 \mu_0 I (a-b) \over \pi^2 a b} \text{[T]}$$
## 3
Consider a cylinder of radius, $\rho_0 = 0.5\text{[m]}$, with a current density, $\vec{J} = 4.5e^{-2\rho}\hat{z}[A/m^2]$.
By Ampere's Law:
$$\int \vec{B} \cdot d\vec{l} = \mu_0 I_{enc}$$
For a radial current density:
$$I_{enc} = \int\limits_{0}^{2\pi} \int\limits_{0}^{\rho} J sdsd\varphi$$
Plugging in $J$ with $s$ as the integrating variable:
$$I_{enc} = \int\limits_{0}^{2\pi} \int\limits_{0}^{\rho} 4.5e^{-2s} sdsd\varphi$$
$$I_{enc} = 4.5\int\limits_{0}^{2\pi} \int\limits_{0}^{\rho} e^{-2s} sdsd\varphi$$
$$I_{enc} = 4.5\int\limits_{0}^{2\pi} \left[ \left( {-\rho \over 2} - {1 \over 4}\right)e^{-2\rho} + {1 \over 4}\right]d\varphi$$
$$\therefore I_{enc} = {9 \pi e^{-2\rho}(e^{2\rho} -2\rho -1) \over 4}$$
Back to Ampere's Law:
$$\int \vec{B} \cdot d\vec{l} = \mu_0 I_{enc}$$
For a circular loop:
$$\int\limits_{0}^{2\pi} B\rho d\varphi = \mu_0 I_{enc}$$
$$B(2\pi\rho) = {9 \pi e^{-2\rho}(e^{2\rho} -2\rho -1) \over 4}$$
For $\rho \le \rho_0$
$$B = {9 e^{-2\rho}(e^{2\rho} -2\rho -1) \over 8\rho}$$
For $\rho \ge \rho_0$:
$$I_{enc} = 4.5\int\limits_{0}^{2\pi} \int\limits_{0}^{\rho_0} e^{-2s} sdsd\varphi = {9 (e-2) \pi \over 4 e}$$
$$B(2\pi\rho) = {9(e-2)\pi \over 4e}$$
$$\therefore B = {9(e-2) \over 8e\rho}\text{[T]}$$
## 4
Consider a solenoidal wire with $n$ coils per unit length. The core becomes magnetized when a current $I=10[A]$ is put into the wire coil, and this causes a bound current to flow around the cylindrical surface of the core as shown in the side view diagram. This bound core surface current density has magnitude, $J = 20n [A/m]$
$$B = B_s + B_c$$
$$B_s = \mu_0 I n = 10\mu_0n$$
Pretend the core current is just another solenoid:
$$B_c = \mu_0 I n = 20\mu_0n$$
$$B = 30\mu_0 n \text{[T]}$$
## 5
A satellite travelling at $5\text{[km/s]}$ enters a current filled curtain. From $t=1\text{[s]}$ to $t=3\text{[s]}$, the satellite's magnetometer increases from $-95\hat{x}\text{[nT]}$ to $95\hat{x}\text{[nT]}$. If the current flows in the $\hat{z}$ direction, find the current density, $J$.
By Ampere's Law:
$$\int \vec{B} \cdot d\vec{l} = \mu_0 \iint \vec{J} \cdot d\vec{s}$$
The total increase in $B$ is $195 \text{[nT]}$, so:
$$195 \times 10^{-9} = \mu_0 \iint \vec{J} \cdot d\vec{s}$$
Plug in bounds to get the total distance through the curtain:
$$195 \times 10^{-9} = \mu_0 \int\limits_{1}^{3} \int\limits_{0}^{-5000} J dvdt$$
$$195 \times 10^{-9} = -10000J\mu_0$$
$$J = {-195 \times 10^{-13} \over \mu_0} \text{[A/m}]$$

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# Homework 3 - Aidan Sharpe
## 1
An particle with charge $-e$ has velocity $\vec{v} = -v\hat{y}$. An electric acts in the $\hat{x}$ direction. What direction must a $\vec{B}$ field act for the net force on the particle to be 0?
$$\vec{F}_{net} = \vec{F}_E + \vec{F}_B = 0$$
$$\therefore \vec{F}_B = -\vec{F}_E$$
$$\vec{F}_E = q\vec{E} = (-)(\hat{x}) = -\hat{x}$$
$$\vec{F}_B = q\vec{v} \times \vec{B}$$
$$(-)\begin{vmatrix}
\hat{x} & \hat{y} & \hat{z} \\
0 & (-) & 0 \\
B_x & B_y & B_z \\
\end{vmatrix} \overset{!}{=} \hat{x}$$
$$-[(-B_z)\hat{x} - (0)\hat{y} + (0-(-)B_x)\hat{z})] \overset{!}{=} \hat{x}$$
$$\therefore \hat{a}_B = \hat{z}$$
## 2
Consider a plane wave in free space with electromagnetic field intensity:
$$\hat{E}e^{j\omega t} = 30\pi e^{j(10^8t + \beta z)}\hat{x}$$
$$\hat{H}e^{j\omega t} = H_m e^{j(10^8t + \beta z)}\hat{y}$$
Find the direction of propagation and the values for $H_m$, $\beta$, and the wavelength.
Since $\beta z$ is added to $\omega t$, propagation is in the $-\hat{z}$ direction.
$${E_x \over H_y} = \mu_0 c$$
$$E_x = 30\pi$$
$$H_y = H_m$$
$$\therefore H_m = {30\pi \over \mu_0 c}$$
$$\boxed{H_m = 0.25}$$
$$\beta = \omega \sqrt{\mu \varepsilon}$$
For free space:
$$\beta = \omega \sqrt{\mu_0 \varepsilon_0}$$
$$\omega = 10^8$$
$$\boxed{\beta = 0.334}$$
$$\lambda = {c \over f}$$
$$f = {\omega \over 2\pi} = {5 \over \pi} \times 10^7$$
$$\lambda = {3 \times 10^8 \over {5 \over \pi} \times 10^7} = {30\pi \over 5}$$
$$\boxed{\lambda = 6\pi\text{[m]}}$$
## 3
A uniform electric field has intensity:
$$\vec{E} = 15\cos\left(\pi \times 10^8t +{\pi \over 3}z\right)\hat{y}$$
The $\vec{E}$ field is polarized in the $\hat{y}$ direction.
The wave will propagate in the $-\hat{z}$ direction.
$$f = {\pi \times 10^8 \over 2\pi} = 5 \times 10^7 \text{[s}^{-1}]$$
$$\lambda = {3 \times 10^8 \over 5 \times 10^7} = 6 \text{[m]}$$
$$H_x = {15 \over \mu_0 c} = 0.0398$$
$$\vec{H} = 0.0398\cos\left(\pi \times 10^8 t + {\pi \over 3}z\right)\hat{x}$$
## 4
### a)
The properties of a uniform basic plane wave in free space are:
Polarization, amplitude, angular frequency, and the direction of propagation. All other properties, such as wavelength, and the spatial frequency, $\beta$, can be derrived.
### b)
A uniform plane wave in free space is propagating in the $\hat{z}$ direction. If the wavelength is $\lambda = 3$[cm].
$$f = {c \over \lambda} = {3 \times 10^8 \over 3 \times 10^{-2}} = 10^{10}\text{[s}^{-1}]$$
$$\beta = 2\pi f \sqrt{\mu_0 \varepsilon_0} = 209.613$$
The amplitude of the x-polarized $\vec{E}$-field is:
$$\hat{E}_m = 200e^{j {\pi \over 4}}$$
Real-time $\vec{E}$-field:
$$\vec{E}(z, t) = 200\cos\left(2\pi \times 10^{10}t - 209.613z + {\pi \over 4}\right)\hat{x}$$
Phasor $\vec{H}$-field:
$$\hat{H} = 0.53e^{j({\pi \over 4} - 209.613z)}\hat{y}$$
Real-time $\vec{H}$-field:
$$\vec{H}(z, t) = 0.53\cos\left(2\pi \times 10^{10}t - 209.613z + {\pi \over 4}\right)\hat{y}$$
## 5
A 25[cm] by 25[cm] circuit in the y-z plane grows in the $\hat{y}$ direction by 10[m/s]. The circuit contains a 5-ohm resitor. Find the current through the circuit if it is placed in a uniform $\vec{B}$ field of $-0.5\hat{x}$[T].
By Ohms law:
$$V = IR$$
$$\mathcal{E} = -{d \over dt} \int \vec{B} \cdot d\vec{s}$$
$$\mathcal{E} = -{d B A(t) \over dt}$$
$$B A(t) = -0.5 \times 0.25(0.25 + 10t) = -1.25t - 0.03125$$
$$\mathcal{E} = -{d B A(t) \over dt} = 1.25 \text{[V]}$$
$$I = {V \over R} = 250\text{[mA]}$$
Since the magnetic flux inside the loop is increasing, and the magnetic field induced by the current must counteract the magnetic field inducing the current, the current must flow counter-clockwise around the loop.
## 6
### a)
```matlab
clear all;
k = 9e9;
q1 = 1.0e-6;
q2 = 1.0e-6;
ax = 1.0;
ay = 0;
bx = -1.0;
by = 0;
[X, Y] = meshgrid(-2:0.9:2,-2:0.9:2);
V = 1./sqrt((X - ax).^2 + (Y-ay).^2 ) * k * q1 + 1./sqrt((X-bx).^2 + (Y-by).^2) * k * q2;
surfc(X, Y, V);
[Ex, Ey] = gradient(-V, 0.2, 0.2);
figure
contour(X, Y, V);
hold on;
quiver(X, Y, Ex, Ey);
```
![](H0306a.png)
### b)
![](H0306b.png)
### c)
```matlab
% Removed the negative sign on q2
q1 = 1.0e-6;
q2 = 1.0e-6;
```
![](H0306c.png)

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# Homework 5 - Aidan Sharpe
## 1
A nonuniform time-varying electric field given in the cylindrical coordinates by:
$$\vec{E} = \left(3\rho^2 \cot(\varphi) \hat{\rho} + {\cos(\varphi) \over \rho}\hat{\varphi}\right) \sin(3 \times 10^8t) [\text{V/m}]$$
The field is applied to the following homogeneous, isotropic dielectric materials:
1. Teflon
- $\mu_r = 1$
- $\varepsilon_r = 2.1$
- $\sigma = 0$
1. Glass
- $\mu_r = 1$
- $\varepsilon_r = 6.3$
- $\sigma = 0$
1. Sea Water
- $\mu_r = 1$
- $\varepsilon_r = 81$
- $\sigma = 4$[S/m]
### a)
Find the polarization vector, the polarization current density, and the polarization charge density for each material.
$$\vec{P} = \varepsilon_0 \chi_e \vec{E}$$
$$\chi_e = \varepsilon_r - 1$$
$$\vec{J}_p = {\partial \over \partial t} \vec{P}$$
$$\rho_p = - \nabla \cdot \vec{P}$$
In cylindrical coordinates:
$$\nabla = {1\over\rho}{\partial (\rho A_\rho) \over \partial \rho} + {1\over\rho}{\partial A_\varphi \over \partial \varphi} + {\partial A_z \over \partial z}$$
For teflon:
$$\vec{P} = \varepsilon_0 (2.1 - 1) \left(9\rho^2 \cot(\varphi) \hat{\rho} + {\cos(\varphi) \over \rho^2}\hat{\varphi}\right) \sin(3 \times 10^8t)$$
$$\vec{J}_p = (3\times10^8)\varepsilon_0 (2.1 -1)\left(9\rho^2 \cot(\varphi) \hat{\rho} + {\cos(\varphi) \over \rho^2}\hat{\varphi}\right) \cos(3 \times 10^8t)$$
$$\nabla \cdot \vec{P} = 1.1 \varepsilon_0 \sin(3\times10^8t)\left[{\partial \over \partial \rho} 9\rho^2\cot(\varphi) + {\partial \over \partial \varphi} {1\over\rho^2}\cos(\varphi)\right]$$
$$\rho_p = 1.1 \varepsilon_0 \sin(3 \times 10^8) \left[-18 \rho \cot(\varphi) + {1\over\rho^2} \sin(\varphi)\right]$$
For glass:
$$\vec{P} = \varepsilon_0(6.3 - 1) \left(9\rho^2 \cot(\varphi) \hat{\rho} + {\cos(\varphi) \over \rho^2}\hat{\varphi}\right) \sin(3 \times 10^8t)$$
$$\vec{J}_p = (3\times10^8)\varepsilon_0 (6.3 -1)\left(9\rho^2 \cot(\varphi) \hat{\rho} + {\cos(\varphi) \over \rho^2}\hat{\varphi}\right) \cos(3 \times 10^8t)$$
$$\nabla \cdot \vec{P} = 5.3 \varepsilon_0 \sin(9\times10^8t)\left[{\partial \over \partial \rho} 9\rho^2\cot(\varphi) + {\partial \over \partial \varphi} {1\over\rho^2}\cos(\varphi)\right]$$
$$\rho_p = 5.3 \varepsilon_0 \sin(9 \times 10^8) \left[-18 \rho \cot(\varphi) + {1\over\rho^2} \sin(\varphi)\right]$$
For sea water:
$$\vec{P} = \varepsilon_0(81 - 1) \left(9\rho^2 \cot(\varphi) \hat{\rho} + {\cos(\varphi) \over \rho^2}\hat{\varphi}\right) \sin(3 \times 10^8t)$$
$$\vec{J}_p = (3\times10^8)\varepsilon_0 (81 -1)\left(9\rho^2 \cot(\varphi) \hat{\rho} + {\cos(\varphi) \over \rho^2}\hat{\varphi}\right) \cos(3 \times 10^8t)$$
$$\nabla \cdot \vec{P} = 80 \varepsilon_0 \sin(3\times10^8t)\left[{\partial \over \partial \rho} 9\rho^2\cot(\varphi) + {\partial \over \partial \varphi} {1\over\rho^2}\cos(\varphi)\right]$$
$$\rho_p = 80 \varepsilon_0 \sin(3 \times 10^8) \left[-18 \rho \cot(\varphi) + {1\over\rho^2} \sin(\varphi)\right]$$
### b)
Find the ratio of the conduction to the displacement currents in the sea water.
$${4 \over J_p} = {1 \over (6\times10^9) \varepsilon_0\left(9\rho^2 \cot(\varphi) \hat{\rho} + {\cos(\varphi) \over \rho^2}\hat{\varphi}\right) \cos(3 \times 10^8t)}$$
**NOTE**: I am unsure why the book seems to be taking a slightly different approach to finding $\rho_p$. In the example we did in class, I was also off by a factor of three, so I am likely missing something here. The example we did in class was:
$$\vec{P} = k\vec{r} = kr\hat{r}$$ Taking the negative of the dot product with $\nabla = {\partial \over \partial r} \hat{r}$ gives me $-k$ and not $-3k$, as you got. ## 2
Three coaxial cylinders separated by two different dielectric are charged as follows:
- The inner cylinder of radius $a$ has a positive linear charge density $\rho_{l1}$[C/m].
- The middle cylinder of radius $b$ is grounded
- The outer cylinder of radius $c$ has negative linear charge density $-\rho_{l2}$[C/m]
### a)
Determine and draw sketches showing the variation of electric flux density and the electric field intensity between the cylinders and outside them.
For the inner cylinder, the electric field inside is 0, and the flux through a cylindrical surface with length, $z$, and radius, $\rho$, enclosing the cylinder is given by Gauss's law:
$$\Phi_E = {Q_\text{enc} \over \varepsilon_0 \varepsilon_r} = {\rho_{l_1} z \over \varepsilon_0 \varepsilon_1} = \int \vec{E} \cdot d\vec{s}$$
By inspection, the electric field strength through the label of the cylinder is uniform, so the surface integral of the electric field evaluates to:
$$E 2\pi \rho z$$
Solving for the $E$-field strength at the surface yields
$$E = {\rho_{l_1} \over 2 \pi \rho \varepsilon_0 \varepsilon_1} : \{a < \rho < b\}$$
Since the middle cylinder is grounded the electric field is defined to be zero at and around its extent.
$$E = 0 : \{b \le \rho \le c\}$$
Outside the large cylinder, more charge is added, this time $-\rho_{l_2}$. The total electric field here is:
$$E = {- \rho_{l_2} \over 2 \pi \rho \varepsilon_0} : \{\rho > c\}$$
The total electric field strength at a distance, $\rho$ is given by the piecewise function:
$$E(\rho) = \begin{cases} {\rho_{l1} \over 2 \pi \rho \varepsilon_0 \varepsilon_1} & a < \rho < b \\ 0 & b \le \rho < c \\ {- \rho_{l_2} \over 2 \pi \rho \varepsilon_0} & \rho > c \\ \end{cases}$$
Using some dummy values to plot the field strength. $\rho_{l1} = 1.5$, $\rho_{l2} = 1.3$, $\varepsilon_0 =1$, $a=1$, $b=2$, $c=3$, $\varepsilon_1 = 1.2$, $\varepsilon_2 = 1.4$.
$$E(\rho) = \begin{cases} {\rho_{l1} \over 2 \pi \rho \varepsilon_0 \varepsilon_1} & a < \rho < b \\ 0 & b \le \rho < c \\ {-\rho_{l_2} \over 2 \pi \rho \varepsilon_0} & \rho > c \\ \end{cases}$$
### b)
Determine the induced surface charge on the middle conductor.
$$\sigma(2 \pi b z) = -\rho_{l_1} z$$
$$\therefore \sigma = -{\rho_{l_1} \over 2\pi b}$$
## 3
An $N$ turn toroid of rectangular cross section consists of 3 regions. Region 1 with relative permeability $\mu_{r_1} = 3000$, region 2 with $\mu_{r_2} = 1 + 2/\rho$, region 3 is air.
### a)
Find the magnetic field intensity, $\vec{H}$, the magnetic flux density, $\vec{B}$, and the magnetization, $\vec{M}$ in each of the three regions.
Region 1:
$$M_1 = (3000 -1) {N I \over 2\pi \rho} = {2998 N I \over 2\pi \rho}\hat{\varphi}$$
$$H_1 = {N_I \over 2\pi \rho}$$
$$B_1 = \mu_0{3000 N I \over 2\pi \rho} = {1500 N I \mu_0 \over \rho}\hat{\varphi}$$
Region 2:
$$M_2 = {2\over \rho}{N I \over 2\pi \rho} = {NI \over 2\pi \rho^2}\hat{\varphi}$$
$$H_2 = {N_I \over 2\pi \rho}$$
$$B_2 = \mu_0\left(1 + {2\over\rho}\right){N I \over 2\pi \rho}\hat{\varphi}$$
Region 3:
$$M_3 = 0\hat{\varphi}$$
$$H_3 = {N_I \over 2\pi \rho}$$
$$B_3 = \mu_0{N I \over 2\pi \rho}\hat{\varphi}$$
### b)
Find the magnetization current density in region 2:
$$J_m = \nabla \times \vec{H} = {1\over\rho}{\partial \vec{H} \over \partial \rho} = -{NI \over \pi\rho^3}$$
## 4
A uniform plane wave is travelling in a medium in the $\hat{x}$ direction. $\lambda = 25$[cm], $v_p= 2 \times 10^8$[m/s], and $\hat{E}$ is polarized in the $\hat{z}$ direction.
### a)
Find the frequency of the wave and $\varepsilon_r$:
$$\lambda = {v_p \over f} \therefore f = {v_p \over \lambda} = 8 \times 10^9[\text{s}^{-1}]$$
$$v_p = {1 \over \sqrt{\mu \varepsilon}}$$
$$\mu = \mu_0$$
$$\varepsilon = \varepsilon_0 \varepsilon_r$$
$$\therefore \varepsilon_r = {1 \over \mu_0 \varepsilon_0 v_p^2} = 2.246$$
### b)
$$\lambda = {2\pi \over \beta} \therefore \beta = 8\pi$$
$$\hat{E} = 50e^{j(16\pi \times 10^9-8\pi x)}\hat{z}$$
$$\hat{H} = -0.1989e^{j(16\pi \times 10^9 - 8\pi x)} \hat{y}$$
## 5
An electromagnetic plane wave of frequency $f$ is given by:
$$\omega = 2\pi f$$
$$\hat{E} = E_0e^{j\omega t - \beta z)}\hat{x}$$
$$\hat{H} = {E_0 \over \eta} \cos(\omega t - \beta z)\hat{y}$$
$$\mathcal{E} = -{d\over dt}\mu \int_s \vec{H} \cdot d\vec{s}$$
$$\mathcal{E} = \mu {E_0 \over \eta} 2\pi\omega \sin(\omega t - \beta z) = \mu {E_0 \over \eta} 2\pi\omega e^{j(\omega t - \beta z - {\pi \over 2})}$$

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# Homework 6 - Aidan Sharpe
## Exercise 1
Consider a solenoid containing two coaxial magnetic rods of radii $a$ and $b$ and permeabilities $\mu_1 = 2\mu_0$ and $\mu_2 = 3\mu_0$. If the solenoid has $n$ turns every $d$ meters along the axis and carries a steady current, $I$.
### a)
Find $\vec{H}$ inside the first rod, between the first and second rod, and outside the second rod.
For a solenoid regardless of magnetic materials:
$$\vec{H} = {I n \over d}\hat{z}$$
So for all regions:
$$\vec{H} = {I n \over d}\hat{z}$$
### b)
Find $\vec{B}$ inside the three regions.
$\vec{B}$ relies on magnetic material properties:
$$\vec{B} = \mu \vec{H}$$
Therefore:
$$\vec{B} = \begin{cases} 2\mu_0\vec{H} & \text{In region 1}\\ 3\mu_0\vec{H} & \text{In region 2}\\ \mu_0\vec{H} & \text{In region 3} \end{cases}$$
### c)
$\vec{M}$ in each region:
By definition:
$$\vec{M} = \chi_m \vec{H}$$
$$\chi_m = \mu_r - 1$$
Therefore:
$$\vec{M} = \begin{cases} \vec{H} & \text{In region 1} \\ 2\vec{H} & \text{In region 2} \\ 0 & \text{In region 3} \end{cases}$$
### d)
$\vec{J}$ in each region:
By definition:
$$\vec{J}_m = \nabla \times \vec{M}$$
Since $\vec{M}$ is both conservative and solenoidal inside the solenoid, for all three regions:
$$\vec{J}_m = 0$$
## Exercise 2
In a nonmagnetic medium:
$$E = 4\sin(2\pi \times 10^7 t - 0.8x)\hat{z}$$
### a)
Find $\varepsilon_r$ and $\eta$:
The general form:
$$\vec{E}(x,t) = E_0\cos(\omega t -\beta x)\hat{z}$$
$$\beta = \omega \sqrt{\mu \varepsilon} = 0.8$$
$$0.8 = 2\pi\times10^7 \sqrt{\mu_0 \varepsilon_0 \varepsilon_r}$$
$${{\left(0.8 \over 2\pi\times10^7\right)^2} \over \mu_0 \varepsilon_0} = \varepsilon_r$$
$$\boxed{\varepsilon_r = 14.566}$$
$$\eta = \sqrt{\mu \over \varepsilon} = \sqrt{\mu_0 \over \varepsilon_0 \varepsilon_r}$$
$$\boxed{\eta = 98.275}$$
### b)
Find the average poynting vector
$$\vec{P}_\text{avg} = {E_0^2 \over 2 \eta}\hat{x} = {4^2 \over 2(98.275)}$$
$$\vec{P}_\text{avg} = 0.081$$
## Exercise 3
$$E = 3\sin(2\pi\times10^7t - 0.4\pi x)\hat{y} + 4\sin(2\pi\times10^7t - 0.4\pi x)\hat{z}$$
### b)
$$\varepsilon_r = {\left({\beta \over \omega}\right)^2 \over \mu_0 \varepsilon_0} = {\left({0.4\pi\over 2\pi\times10^7}\right)^2 \over \mu_0 \varepsilon_0}$$
$$\boxed{\varepsilon_r = 35.941}$$
### a)
$$\lambda = {v_p \over f}$$
$$v_p = {1 \over \sqrt{\mu \varepsilon}} = {1 \over \sqrt{\mu_0 \varepsilon_0 \varepsilon_r}} = 5\times10^7$$
$$f = {\omega \over 2\pi} = 10^7$$
$$\boxed{\lambda = 5\text{[m]}}$$
### c)
$$H = {E_0 \over \eta}\sin(\omega t - \beta x)\hat{z} + {E_0' \over \eta}\sin(\omega t - \beta x)\hat{y}$$
$$\eta = \sqrt{\mu_0 \over \varepsilon_0 \varepsilon_r} = 62.85$$
$$\boxed{H = 0.0477\sin(2\pi\times10^7t - 0.4\pi x)\hat{z} + 0.0636\sin(2\pi\times10^7t -0.4\pi x)\hat{y}}$$
## Exercise 4
Prove that:
$$\hat{H}_y = - {\hat{E}_x \over \eta_0}$$
Starting with a genering electric plane wave in the $-\hat{z}$ direction:
$$\vec{E}(z, t) = E_0 \cos(\omega t + \beta_0 z)\hat{x}$$
We will use Faraday's Law of Induction to convert a measure in the $\vec{E}$-field to a value for the $\vec{B}$-field:
$$\nabla \times \vec{E} = -{\partial \over \partial t}\vec{B}$$
Converting from $\vec{B}$ to $\vec{H}$:
$$\nabla \times \vec{E} = -\mu{\partial \over \partial t} \vec{H}$$
Assuming free space:
$$\mu = \mu_0$$
This gives the final form for Faraday's Law:
$$\nabla \times \vec{E} = -\mu_0 {\partial \over \partial t} \vec{H}$$
Evaluating the curl of $\vec{E}$:
$$\nabla \times \vec{E} = \begin{vmatrix} \hat{x} & \hat{y} & \hat{z} \\ {\partial \over \partial x} & {\partial \over \partial y} & {\partial \over \partial z} \\ \|\vec{E}\| & 0 & 0 \end{vmatrix} = {\partial \over \partial z}\|\vec{E}\|\hat{y} - {\partial \over \partial y}\|\vec{E}\|\hat{z}$$
Since $\vec{E}$ only varies with respect to $z$ and $t$ this can be rewritten as:
$$\nabla \times \vec{E} = {\partial \over \partial{z}}\|\vec{E}\|\hat{y}$$
Evaluate the partial derivative:
$$\nabla \times \vec{E} = -E_0\beta_0\sin(\omega t + \beta_0 z)\hat{y}$$
Back to Faraday's Law:
$$-E_0\beta_0\sin(\omega t + \beta_0 z)\hat{y} = -\mu_0{\partial \over \partial t} \vec{H}$$
Divide out by $-\mu_0$:
$${\partial \over \partial t}\vec{H} = {E_0 \beta_0 \over \mu_0}\sin(\omega t + \beta_0 z)\hat{y}$$
Expand out $\beta_0$:
$$\beta_0 = \omega \sqrt{\mu_0 \varepsilon_0}$$
$${\partial \over \partial t}\vec{H} = {E_0 \omega \sqrt{\mu_0 \varepsilon_0} \over \mu_0}\sin(\omega t + \beta_0 z)dt\hat{y}$$
Integrate both sides with respect to $t$:
$$\vec{H}(z,t) = {E_0 \omega \sqrt{\mu_0 \varepsilon_0} \over \mu_0}\int\sin(\omega t + \beta_0 z)dt \hat{y}$$
Evaluate the integral:
$$\vec{H}(z,t) = -{E_0 \omega \sqrt{\mu_0 \varepsilon_0} \over \mu_0 \omega} \cos(\omega t + \beta_0 z)\hat{y}$$
Simplifying the fraction:
$$\vec{H}(z,t) = -E_0 \sqrt{\varepsilon_0 \over \mu_0} \cos(\omega t + \beta_0 z)\hat{y}$$
Using the definition of $\eta_0$:
$$\eta_0 = \sqrt{\mu_0 \over \varepsilon_0}$$
$$\vec{H}(z,t) = -{E_0 \over \eta_0}\cos(\omega t + \beta z)\hat{y}$$
$$\therefore \vec{H}(z,t) = -{\|\vec{E}(z,t)\| \over \eta_0}\hat{y}$$

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# Homework 8 - Aidan Sharpe
## 1
A transmission line is terminated with a matched 50$\Omega$ load. The transmitter puts out 100W of power, and the transmission line is 100ft long. What for what value of $\alpha$ will the power loss be 10W over the length of the line?
$$\alpha = {\ln\left({P_\text{in} \over P_\text{out}}\right) \over l} = {\ln\left({100 \over 90}\right) \over 30.48[\text{m}]} = 0.00345671\left[{\text{np} \over \text{m}}\right]$$
## 2
Evaluate the phase velocity and attenuation constant for a distorionless line, and compare it to a lossless line.
$$\gamma = \alpha + j\beta = \sqrt{(R + j\omega L)(G + j\omega C)}$$
$$\gamma ^2 = (R + j\omega L)(G + j\omega C)$$
$$\gamma^2 = \omega^2 LC(j + {R \over \omega L})(j + {G \over \omega C})$$
For a distorionless line:
$${R \over L} = {G \over C}$$
$$(j + {R \over \omega L}) = (j + {G \over \omega C})$$
So $\gamma^2$ becomes:
$$\gamma^2 = \omega^2 L C (j + {R \over \omega L})^2$$
Solving for $\gamma$
$$\gamma = \omega\sqrt{L C}(j + {R \over \omega L})$$
Separating the real and imaginary components:
$$\alpha = R \sqrt{C \over L}$$
$$\beta = j\omega\sqrt{L C}$$
For a lossless line, there is no attenuation (by definition). Therefore:
$$\alpha = 0$$
To actually be able to build this lossless line, $R=0$ and $G=0$.
$$\gamma^2 = (R + j\omega L)(G + j\omega C)$$
Since $R$ and $G$ are both 0:
$$\gamma^2 = (j\omega L)(j \omega C)$$
$$\gamma^2 = -\omega^2 LC$$
$$\gamma = \sqrt{-\omega^2 LC} = j\omega\sqrt{LC}$$
Separating out real and imaginary:
$$\alpha = 0$$
$$\beta = j\omega\sqrt{LC}$$
For lossless and distortionless lines, the attenuation constant differs, but the phase constant does not. Since the phase velocity only depends on $\omega$ and $\beta$, $v_p$ is the same for both lossless and distortionless lines.
$$v_p = {\omega \over \beta} = {-j \over \sqrt{LC}}$$
## 3
$$\hat{Z}_L = 75 + j150 \Omega$$
$$f = 2[\text{MHz}]$$
$$\omega = 2\pi f = 4\pi \times 10^6$$
$$r = 150\left[{\Omega \over \text{km}}\right]$$
$$l = 1.4\left[{\text{mH} \over \text{km}}\right]$$
$$c = 88\left[{\text{nF} \over \text{km}}\right]$$
$$g = 0.8\left[{\mu\text{s} \over \text{km}}\right]$$
$$\hat{V}_G = 100 e^{j0^\circ}$$
$$z = 100[\text{m}]$$
$$R = 15[\Omega]$$
$$L = 140[\mu\text{H}]$$
$$C = 8.8[\text{nF}]$$
$$G = 80[n\Omega]$$
### a)
Find $\hat{Z}_0$:
$$Z_0 = \sqrt{R + j\omega L \over G + j\omega C} = \sqrt{15 + j(4\pi\times10^6)(140\times10^{-6}) \over 80\times10^{-9} + j(4\pi \times 10^6)(8.8\times10^{-9})}$$
$$Z_0 = 126.1324 - j0.5377$$
$$\hat{\gamma} = \alpha + j\beta = \sqrt{(R + j\omega L)(G + j\omega C)}$$
$$\hat{\gamma} = 0.0595 + j13.9482$$
### b)
Find the input imedance
$$Z_\text{in} = Z_0{Z_L + Z_0 \tanh(\gamma z) \over Z_0 + Z_L \tanh(\gamma z)}$$
$$Z_\text{in} = -126.1324 + j0.5377$$
### c)
Find the average power delivered
$$\alpha = {\ln\left({P_\text{in} \over P_\text{out}}\right) \over z}$$
$$\alpha = 0.0595$$
$$P_\text{in} = {V_G^2 \over Z_\text{in}} = 79.2802 + j0.3373$$
$$P_\text{out} = P_\text{in} e^{-\alpha z} = 0.2073 + j0.0009$$
## 4
$$\Gamma = {Z_L - Z_0 \over Z_L + Z_0}$$
### a)
$$Z_L = 3 Z_0$$
$$\Gamma = 0.5$$
### b)
$$Z_L = (2 - j2)Z_0$$
$$\Gamma = 0.5385 - j0.3077$$
### c)
$$Z_L = -j2Z_0$$
$$\Gamma = 0.6 - j0.8$$
### d)
$$Z_L = 0$$
$$\Gamma = -1$$
## 5
### a)
$$\Gamma = 0.06+j0.24$$
### b)
$$\text{VWSR} = {1 + |\Gamma| \over 1 - |\Gamma|} = 1.657$$
### c)
$$Z_\text{in} = Z_0 {Z_L + Z_0\tanh(\gamma l) \over Z_0 + Z_L\tanh(\gamma l)} 30.50 - j1.09$$
### d)
$$Y_\text{in} = {1 \over Z_in} = 0.03274 + j0.0012$$
### e)
$$0.106\lambda$$
### f)
$$z = -0.106\lambda$$
## 6
$$L = {3\lambda \over 8}$$
$$Z_\text{in} = -j2.5$$
$$Z_L = {-j2.5 \over 100} = -j0.025$$
At ${3\lambda \over 8}$:
$$Z_L = j95$$

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