ELEC 3310 Practice Exam 3
Spring 2024
Write your name on this page and all pages of scratch paper. Show your work and state any
assumptions used. Clearly indicate your final answer on your scratch work by drawing a box
around it and include units in your answer where necessary.
Submit all scratch paper. All problems are graded out of 4 points.
1. Two infinite line currents are arranged in the z-plane as shown in Figure 1. Determine the magnetic
field intensity at the origin. Assume the two currents are not affected by their intersection.
Figure 1: Two infinite wires with current I. (Note that the grey lines are dimensions.
2. No surface current densities exist at the parallel interfaces shown in Figure 2; show that the relation
between θ1 and θ4 does not depend on µ2. Your solution should be an equation which relates θ1 to θ4
and only involves µ1 and µ3. (And maybe a trigonometric function!)
Figure 2: Three parallel slabs with differing permeabilities.
3. Determine the force per unit length on the current labelled I3 in Figure 3. Each current travels into the
paper. I1 = I2 = I3 = 10 A.
Figure 3: Three currents in parallel, flowing into the paper.
4. Consider the circuit shown in Figure 4. The circuit is in a spatially uniform field with time-function
B⃗ = −3tzˆ [T], where t is time and T is Tesla. Determine the voltage (including polarity) across each
resistor. Are these resistors in series or parallel?
Figure 4: A two-resistor circuit in a spatially-uniform but time-varying magnetic field.
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