When the switch is closed, what happens?
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
P4. If the upper right bulb is removed, the voltage difference across the left bulbs A. increases B. decreases C. stays the same
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
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
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
Magnetic fields from a straight wire All currents create magnetic fields B. Unit Tesla: 1T = 1N/(A m) r A right hand rule
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
Ferromagnetic material responds to B field and creates its own larger B field.
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
2/3 cows worldwide face roughly north-south Magnetic iron structure in brains of whales, fish, birds, rodents, cows…
Dogs prefer to line up N-S (+-10 degrees) before they poop 2014 study
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.
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?
Circular or spiral motion B can “reflect” or “trap” charges
Forces on currents from B caused by other moving charges Use the same RHR as for q to find F’s direction
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
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
Torques on current loops Direction of torque: N pole of coil wants to move toward S pole of magnets.
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
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
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
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