*assignment*Mass Density*assignment*Homework##### Mass Density

Static Fields 2023 (4 years) Consider a rod of length \(L\) lying on the \(z\)-axis. Find an algebraic expression for the mass density of the rod if the mass density at \(z=0\) is \(\lambda_0\) and at \(z=L\) is \(7\lambda_0\) and you know that the mass density increases- linearly;
- like the square of the distance along the rod;
- exponentially.

*group*Proportional Reasoning*group*Small Group Activity10 min.

##### Proportional Reasoning

Static Fields 2023 (3 years) In this small group activity, students calculate a (linear) function to represent the charge density on a one-dimensional rod from a description of the charge density in words.*assignment*Electric Field from a Rod*assignment*Homework##### Electric Field from a Rod

Static Fields 2023 (5 years) Consider a thin charged rod of length \(L\) standing along the \(z\)-axis with the bottom end on the \(xy\)-plane. The charge density \(\lambda\) is constant. Find the electric field at the point \((0,0,2L)\).*assignment*Line Sources Using Coulomb's Law*assignment*Homework##### Line Sources Using Coulomb's Law

Static Fields 2023 (6 years)- Find the electric field around a finite, uniformly charged, straight rod, at a point a distance \(s\) straight out from the midpoint, starting from Coulomb's Law.
- Find the electric field around an infinite, uniformly charged, straight rod, starting from the result for a finite rod.

*assignment*Differential Form of Gauss's Law*assignment*Homework##### Differential Form of Gauss's Law

Static Fields 2023 (6 years)For an infinitesimally thin cylindrical shell of radius \(b\) with uniform surface charge density \(\sigma\), the electric field is zero for \(s<b\) and \(\vec{E}= \frac{\sigma b}{\epsilon_0 s}\, \hat s\) for \(s > b\). Use the differential form of Gauss' Law to find the charge density everywhere in space.

*computer*Visualizing Flux through a Cube*computer*Computer Simulation30 min.

##### Visualizing Flux through a Cube

Static Fields 2023 (6 years) Students explore the effects of putting a point charge at various places inside, outside, and on the surface of a cubical Gaussian surface. The*Mathematica*worksheet or*Sage*activity shows the electric field due to the charge, then plots the the flux integrand on the top surface of the box, calculates the flux through the top of the box, and the value of the flux through the whole cube.*group*Magnetic Vector Potential Due to a Spinning Charged Ring*group*Small Group Activity30 min.

##### Magnetic Vector Potential Due to a Spinning Charged Ring

Static Fields 2023 (6 years)compare and contrast mathematica magnetic vector potential magnetic fields vector field symmetry

Students work in small groups to use the superposition principle \[\vec{A}(\vec{r}) =\frac{\mu_0}{4\pi}\int\frac{\vec{J}(\vec{r}^{\,\prime})}{\vert \vec{r}-\vec{r}^{\,\prime}\vert}\, d\tau^{\prime}\] to find an integral expression for the magnetic vector potential, \(\vec{A}(\vec{r})\), due to a spinning ring of charge.

In an optional extension, students find a series expansion for \(\vec{A}(\vec{r})\) either on the axis or in the plane of the ring, for either small or large values of the relevant geometric variable. Add an extra half hour or more to the time estimate for the optional extension.

*assignment*Electric Field and Charge*assignment*Homework##### Electric Field and Charge

divergence charge density Maxwell's equations electric field Static Fields 2023 (4 years) Consider the electric field \begin{equation} \vec E(r,\theta,\phi) = \begin{cases} 0&\textrm{for } r<a\\ \frac{1}{4\pi\epsilon_0} \,\frac{Q}{b^3-a^3}\, \left( r-\frac{a^3}{r^2}\right)\, \hat r & \textrm{for } a<r<b\\ 0 & \textrm{for } r>b \\ \end{cases} \end{equation}- Use step and/or delta functions to write this electric field as a single expression valid everywhere in space.
- Find a formula for the charge density that creates this electric field.
- Interpret your formula for the charge density, i.e. explain briefly in words where the charge is.

*assignment*Gravitational Field and Mass*assignment*Homework##### Gravitational Field and Mass

Static Fields 2023 (5 years)The gravitational field due to a spherical shell of matter (or equivalently, the electric field due to a spherical shell of charge) is given by: \begin{equation} \vec g = \begin{cases} 0&\textrm{for } r<a\\ -G \,\frac{M}{b^3-a^3}\, \left( r-\frac{a^3}{r^2}\right)\, \hat r & \textrm{for } a<r<b\\ -G\,\frac{M}{r^2}\, \hat r & \textrm{for } r>b \\ \end{cases} \end{equation}

This problem explores the consequences of the divergence theorem for this shell.

- Using the given description of the gravitational field, find the divergence of the gravitational field everywhere in space. You will need to divide this question up into three parts: \(r<a\), \(a<r<b\), and \(r>b\).
- Briefly discuss the physical meaning of the divergence in this particular example.
- For this gravitational field, verify the divergence theorem on a sphere, concentric with the shell, with radius \(Q\), where \(a<Q<b\). ("Verify" the divergence theorem means calculate the integrals from both sides of the divergence theorem and show that they give the same answer.)
- Briefly discuss how this example would change if you were discussing the electric field of a uniformly charged spherical shell.

*assignment*Symmetry Arguments for Gauss's Law*assignment*Homework##### Symmetry Arguments for Gauss's Law

Static Fields 2023 (5 years)Instructions for 2022: You will need to complete this assignment in a 15 minute appointment on Zoom or in person with one of the members of the teaching team between 1/21 and 10 pm on 1/26. Here is a link to a sign-up page.

You are required to watch a sample video for how to make symmetry arguments here. As demonstrated in the video you should bring with you to the meeting a cylinder, an observer, and a vector.

Use good symmetry arguments to find the possible direction for the electric field due to a charged wire. Also, use good symmetry arguments to find the possible functional dependence of the electric field due to a charged wire. Rather than writing this up to turn in, you should find a member of the teaching team and make the arguments to them verbally.

- Static Fields 2023 (4 years) Consider a thin charged rod of length \(L\) standing along the \(z\)-axis with the bottom end on the \(x,y\)-plane. The charge density \(\lambda_0\) is constant. Find the total flux of the electric field through a closed cubical surface with sides of length \(3L\) centered at the origin.