There is no current in the wire. A long, straight wire extends into and out of the screen. The current in the wire is Into the screen. Out of the screen. There is no current in the wire. Not enough info to tell the direction. 1

B field of two wires 2

The magnet field at point P is Into the screen. Out of the screen. To the left. To the right. Zero. 3

The direction of the magnetic force on the proton is To the right. To the left. Into the screen. Out of the screen. The magnetic force is zero. 4

A proton is shot straight at the center of a long, straight wire carrying current into the screen. The proton will Go straight into the wire. Hit the wire in front of the screen. Hit the wire behind the screen. Be deflected over the wire. Be deflected under the wire. 5

The direction of the magnetic force on the electron is Upward. Downward. Into the screen. Out of the screen. The magnetic force is zero. 6

It can’t be done with this magnetic field. The horizontal wire can be levitated – held up against the force of gravity – if the current in the wire is Right to left. Left to right. It can’t be done with this magnetic field. 7

Charge and moving magnet A bar magnet moves past an electron as shown. Then the electron at the moment shown Feels no force Feels an upwards force Feels a downward force Feels a force out of the page Feels a force into the page. 8

B Field of Rings Qualitatively from Biot-Savart 9

Where is the north magnetic pole of this current loop? Top side. Bottom side. Right side. Left side. Current loops don’t have north poles. 10

What is the current direction in the loop? Out at the top, in at the bottom. In at the top, out at the bottom. Either A or B would cause the current loop and the bar magnet to repel each other. 11

The current in this solenoid Enters on the left, leaves on the right. Enters on the right, leaves on the left. Either A or B would produce this field. 12

The line integral of B around the loop is 0 · 7.0 A. Current I3 is 1 A out of the screen. 1 A into the screen. 5 A out of the screen. 5 A into the screen. 13

For the path shown, 0. 0(I1  I2). 0(I2  I1). 0(I1  I2). 14

Solenoid 2 has twice the diameter, twice the length, and twice as many turns as solenoid 1. How does the field B2 at the center of solenoid 2 compare to B1 at the center of solenoid 1? B2  B1/4. B2  B1/2. B2  B1. B2  2B1. B2  4B1. 15

Magnetic fields deflect moving charged particles Electron beam bent into circular or helical path by magnetic field due to nearby currents.

At the blackboard: Coulomb's law plus special relativity explains strange cross-product rule

Which magnetic field causes the observed force? 18

Which magnetic field (if it’s the correct strength) allows the electron to pass through the charged electrodes without being deflected? 19

If released from rest, the current loop will Move upward. Move downward. Rotate clockwise. Rotate counterclockwise. Do something not listed here. 20