Instructor Survey:
Colorado Upper-Division Electrostatics (CUE) Assessment
Thank you for taking the time to answer and rate these assessment questions. The Colorado Upper-Division Electrostatics (CUE) Assessment is an instrument designed to test whether juniors successfully gain some of the key skills in E&M I. This survey asks you to both answer these questions (so that we may identify problems with the questions) and indicate whether you think that they adequately address the learning goals of the course.
First, you will be asked to answer the question. Where you are asked to sketch, describe the sketch you would draw as best as you can. Below each question we have listed a course learning goal, so you can get a better idea of where we feel each question fits into an electricity and magnetism course curriculum. After you answer each assessment question, please rate its quality by answering 3 follow up questions.
Name: Institution:
Please Note: Once your information comes back to us, we will assign you a random number and will only reveal your answers and opinions in an anonymous manner.
SECTION 1: CHOOSING A METHOD
For each of the following 17 questions, give a brief outline of the EASIEST method that you would use to solve the problem. Methods used in this class include but are not limited to: Direct Integration, Ampere's Law, Superposition, Gauss' Law, Method of Images, Separation of Variables, and Multipole Expansion. DO NOT SOLVE the problem, we just want to know:
Example problem: Find the electric field at point P outside a uniformly charged sphere, with total charge +Q.
Example problem:
Find the electric field at point P outside a uniformly charged sphere, with total charge +Q.
Example Response: Gauss' Law with a spherical Gaussian surface centered around the origin. Because the E field is symmetric in theta and phi.
Example Response:
Gauss' Law with a spherical Gaussian surface centered around the origin. Because the E field is symmetric in theta and phi.
Course Learning Goal: (1) Problem-solving: Students should be able to choose the problem-solving technique that is appropriate to a particular problem. They should be able to apply these problem-solving approaches to novel contexts (i.e., to solve problems which do not map directly to those in the book), indicating that they understand the essential features of the technique rather than just the mechanics of its application. They should be able to justify their approach for solving a particular problem. (2) Communicaton: Students should be able to justify and explain their thinking and/or approach to a problem or physical situation, in either written or oral form. Topic Learning Goal: Students should recognize where separation of variables is applicable and what coordinate system is appropriate to separate in.
Course Learning Goal: (1) Problem-solving: Students should be able to choose the problem-solving technique that is appropriate to a particular problem. They should be able to apply these problem-solving approaches to novel contexts (i.e., to solve problems which do not map directly to those in the book), indicating that they understand the essential features of the technique rather than just the mechanics of its application. They should be able to justify their approach for solving a particular problem. (2) Communicaton: Students should be able to justify and explain their thinking and/or approach to a problem or physical situation, in either written or oral form. Topic Learning Goal: Students should be able to state Coulomb’s Law and use it to solve for E above a line of charge, a loop of charge, and a circular disk of charge.
SECTION 2: GENERAL QUESTIONS
You are given a non-conducting sphere, centered at the origin. The sphere has a non-uniform, positive and finite volume charge density ρ(r). You notice that another student has set the reference point for V such that V=0 at the center of the sphere: V(r=0)=0.
What would V=0 at r=0 imply about the sign of the potential at r→∞? (a) V (r→∞) is positive (+) (b) V (r→∞) is negative (-) (c) V (r→∞) is zero (d) It depends
You are given an infinite solid conducting cylinder whose vertical axis runs along the y direction, that is placed in an external electric field, , as in the figure to the right. The cylinder extends infinitely in the +y and –y directions. On the two-dimensional figure below:
(a) Sketch the induced charge, σ. (b) Sketch the electric field everywhere.
For the conducting cylinder shown above we want to use the method of separation of variables to solve for:
(a) the potential everywhere and (b) the surface charge sigma. List the boundary conditions on V and/or E at the surface needed to do this. Do not solve for V, just tell us the boundary conditions on V or E.
The following set of problems refers to the uniform flat, thin disk of radius R carrying uniform positive surface charge density +σ0 as in the figure.
What is the value of the z-component of the electric field (Ez) very near the origin (z<<R)?
How does Ez behave as a function of z as you get very far from the disk (z>>R)?
Draw a qualitative graph of Ez as you move away from the disk, along the z-axis.
We are looking for the relative magnitude and sign of Ez as a function of distance from the disk, not field lines. Include both z>0 and z<0 on your graph.
Draw a qualitative graph of V as you move away from the disk, along the z-axis. Include both z>0 and z<0.
What is a physical interpretation of the behavior of E (or V) near the origin?
You are given a 2-D box with potentials specified on the boundary as indicated in the figures below. The general solution to Laplace’s equation in Cartesian coordinates is OR . That is, you can choose to associate the sin and cos with either the x or y coordinate. To solve this by separation of variables, which form of the solution should you choose?
a)
b) c) It doesn't matter.
A dielectric is inserted into an isolated infinite parallel plate capacitor, as shown.
Using concepts and terminology you’ve learned in Phys3310, explain how the insertion of the dielectric reduces the electric field in the capacitor.
What physical quantities would change (and how) in the limit that the dielectric constant approaches that of a perfect conductor?
Circle all of the following boundary conditions that are suitable for solving Laplace’s equation for finding V(r,θ) everywhere due to a charge density σ on a spherical surface of radius R.
(I) Vin=Vout at r=R
(II) at r=R
(III) at r=R
(IV) at r=R
You are given the following charge distribution made of 4 point charges, each located a distance “a” from the x- and y-axis.
Is the dipole moment of this distribution zero? (a) Yes (b) No (c) Not sure
Consider an infinite non-magnetizeable cylinder with a uniform volume current density J.
Where is the B field maximum? Explain how to determine this.
Thank you for taking the time to answer these assessment questions. If you have any additional comments about this survey as a whole, please enter them here: