What do you expect for direction of $\mathbf{B}(P)$? How about direction of $d\mathbf{B}(P)$ generated JUST by the segment of current $d\mathbf{l}$ in red? <img src="./images/curvy_wire_current.png" align="center" style="width: 400px";/> 1. $\mathbf{B}(P)$ in plane of page, ditto for $d\mathbf{B}(P$, by red$)$ 2. $\mathbf{B}(P)$ into page, $d\mathbf{B}(P$, by red$)$ into page 3. $\mathbf{B}(P)$ into page, $d\mathbf{B}(P$, by red$)$ out of page 4. $\mathbf{B}(P)$ complicated, ditto for $d\mathbf{B}(P$, by red$)$ 5. Something else!! Note: * CORRECT ANSWER: C

## Announcements * Danny out of town this Wednesday; Dennis will lecture * Homework 9 due this Friday * Homework 10 due Dec. 2nd (after Thanksgiving holiday) * No help session week of Thanksgiving * But, we will have class on Wednesday

What is the magnitude of $\dfrac{d\mathbf{l}\times\hat{\mathfrak{R}}}{\mathfrak{R}^2}$? <img src="./images/ringcurrent_R.png" align="right" style="width: 400px";/> 1. $\frac{dl \sin\phi}{z^2}$ 2. $\frac{dl}{z^2}$ 3. $\frac{dl \sin\phi}{z^2+a^2}$ 4. $\frac{dl}{z^2+a^2}$ 5. something else! Note: * CORRECT ANSWER: D

What is $d\mathbf{B}_z$ (the contribution to the vertical component of $\mathbf{B}$ from this $d\mathbf{l}$ segment?) <img src="./images/ringcurrent_R.png" align="right" style="width: 400px";/> 1. $\frac{dl}{z^2+a^2}\frac{a}{\sqrt{z^2+a^2}}$ 1. $\frac{dl}{z^2+a^2}$ 1. $\frac{dl}{z^2+a^2}\frac{z}{\sqrt{z^2+a^2}}$ 1. $\frac{dl \cos \phi}{\sqrt{z^2+a^2}}$ 5. Something else! Note: * CORRECT ANSWER: A

<img src="./images/parallel_currents.png" align="right" style="width: 250px";/> I have two very long, parallel wires each carrying a current $I_1$ and $I_2$, respectively. In which direction is the force on the wire with the current $I_2$? 1. Up 2. Down 3. Right 4. Left 5. Into or out of the page Note: * CORRECT ANSWER: D