Consider two situations:
1) Loop moves to right with speed $\lvert v\rvert$
2) Magnet moves to left with (same) speed $\lvert v\rvert$
<img src="./images/loop_in_Bfield_ammeter.png" align="left" style="width: 500px";/> What will the ammeter read in each case? (Assume that CCW current => positive ammeter reading) 1. $I_1$>0, $I_2$=0 2. $I_1$= $I_2$ > 0 3. $I_1$= -$I_2$ > 0 4. $I_1$= $I_2$ = 0 5. Something different/not sure Note: * Correct Answer: B

## Announcements * Homework 4 (Due Feb 8) * Project problem is longer! * Quiz 2 - Next Friday (Motional EMF) * Discuss the differences between: * $\mathcal{E} = \oint \mathbf{f} \cdot d\mathbf{l}$ and $\mathcal{E} = -\frac{d\Phi_B}{dt}$ * Solve a motional EMF problem and discuss the direction of the current * DC out of town (Feb 4-8) * Rachel Henderson will cover * Film crew will be here on Wednesday

Faraday found that EMF is proportional to the negative time rate of change of B. EMF is also the line integral of a **force/charge**. The force is $\mathbf{f}_q$ in the expression: $$\mathcal{E} = \oint \mathbf{f}_q \cdot d\mathbf{l}$$ That force is: 1. the magnetic Lorentz force. 2. an electric force. 3. the strong nuclear force. 4. the gravitational force. 5. an entirely new force. Note: * Correct Answer: B, but there's a subtlety here; could E (special relativity)

A stationary rectangular metal loop is in a region of uniform magnetic field $\mathbf{B}$, which has magnitude B decreasing with time as $B=B_0-kt$. What is the direction of the field induced B-field created by the induced current in the loop, in the plane region inside the loop? <img src="./images/loop_in_Bfield_2.png" align="right" style="width: 500px";/> 1. Into the screen 2. Out of the screen 3. To the left 4. To the right 5. other/?? Note: * Correct Answer: B

A rectangular metal loop is moving thru a region of constant uniform magnetic field $\mathbf{B}$, out of page, with constant speed $v$, as shown. Is there a non-zero emf around the loop? <img src="./images/loop_in_Bfield_3.png" align="right" style="width: 500px";/> 1. Yes, current will flow CW 2. Yes, current will flow CCW 3. No Note: * Correct Answer: C

A loop of wire is near a long straight wire which is carrying a large current $I$, which is **decreasing**. The loop and the straight wire are in the same plane and are positioned as shown. The current induced in the loop is: 1. counter-clockwise 2. clockwise 3. zero. <img src="./images/loop_near_wire.png" align="center" style="width: 700px";/> Note: * Correct Answer: B