1. When the switch is closed, what happens?

2. P3. The circuit starts with 4 bulbs
P3. The circuit starts with 4 bulbs. If the upper right bulb is removed, leaving an air gap, the current through the battery_____. A. increases B. decreases C. stays the same

3. P4. If the upper right bulb is removed, the voltage difference across the left bulbs A. increases B. decreases C. stays the same

4. P7. After we close the switch, and before the C has charged much at all, the current through the battery is closest to _______ A. A. 1 B. 2 C. 3 D. 4 E. 5 P8. After we close the switch, and C is fully charged, the current through the battery is closest to _______ A. A. 0 B. 2 C. 3 D. 4 E. 5

5. Magnetic fields are created by moving charges
In atoms: electrons, protons have orbits and spin create magnetic fields
Magnetic fields form loops. Lines come out of a “North” magnetic pole and into a “South” magnetic pole

6. Magnetic field from circular current loops
All currents create magnetic fields B. Unit Tesla: 1T = 1N/(A m)
“Right hand rule”: Curl fingers in the direction of the current in a loop or coil. Thumb is in the direction of B coming out the loop, and that side is the N pole of the “magnetic moment” it creates

7. Magnetic fields from a straight wire
All currents create magnetic fields B. Unit Tesla: 1T = 1N/(A m) r
A right hand rule

8. Solenoid (coil with N turns, length L)
P1. The current flow is shown by the blue arrows inside, the solenoid B is to the ___ (you can use either RH rule)
left
right

9. Ferromagnetic material responds to B field and creates its own larger B field.

10. Magnetic fields are created by moving charges
Earth’s field comes from charged molten flows inside
Earth’s “N Pole” is a magnetic S pole…
it attracts the “N” pole of a compass

11. 2/3 cows worldwide face roughly north-south
Magnetic iron structure in brains of whales, fish, birds, rodents, cows…

12. Dogs prefer to line up N-S (+-10 degrees) before they poop
2014 study

13. Magnetic field B creates a force on moving charges
We use a “right-hand-rule” to get the direction of F from qv and B. F is out of your palm.
Force directions are opposite for + and – charges.

14. What is the direction of the force on the charge in a). P2. … in b). A
What is the direction of the force on the charge in a)? P2. … in b)? A. up B. Down C. into page D. out of pg E. zero … in c)? P3. … in d)? P4. If both are the same q and v, which is a bigger force: A or D?

15. Circular or spiral motion
B can “reflect” or “trap” charges

16. Forces on currents from B caused by other moving charges
Use the same RHR as for q to find F’s direction

17. Forces between wire and a charge
P4. What force does the red current exert on the + charge?
A. right
B. left
C. into page
D. out of page

18. Forces between wire with currents
P4. Due to magnetic fields they create (that act only on the other), the two wires will be _____
A. repelled B. attracted
P5. The force on the upper part of the vertical wire, from the field due to the horizontal wire is
A. right
B. left
C. into page
D. out of page

19. Torques on current loops
Direction of torque: N pole of coil wants to move toward S pole of magnets.

20. P8. The net force of the wire on the current loop is A. to the right
B. to the left
C. out of the page
D. into the page
E. zero
P9. The current loop will experience
A. a torque: the left side rotates toward you
B. a torque: the right side rotates toward you
C. no toque

21. P10. You are viewing the top of a solenoid, with current flowing clockwise through it. A proton (purple) is fired just above the solenoid. What’s the force on the proton due to the solenoid’s field? A. to the right B. to the left C. out of the page D. into the page

22. P11. What is the direction that a positive charge needs to move to have the force shown?  up
B. Down
C. into page
D. out of pg
E. zero

23. P6. At the point P, the B fields created by the two wires A. add B
P6. At the point P, the B fields created by the two wires A. add B. cancel P7. The same current flows through both wires. At the point P, the total B field points A. up the page B. down the page C. into the page D. out of the page