- Computers are NOT needed for lab this week
- Jeff will print enough copies of the three magnet templates for all students
- Template printing options: single sided and sort (not collated!)
- There are 4 primary experiments set up: B around bar magnet (2 stations); B around solenoid; B around small coil; B around straight wire (uses the vertical segment of the square wire coil). Since all groups share the apparatus, the order that experiments are performed does not matter
- The solenoid is powered by a dual-power supply. Depending on the power supply used, two buttons may need to be pressed to turn it on: the main Power and the Output buttons
- Calculating B for solenoid:
- During setup, several of the stations have many compasses in place for students to visualize B. Those compasses have been chosen so that they all point in the same direction. If a compass is found to be reversed, replace it with a correctly oriented compass, and set the backward one aside for repair
- An ancient computer with a CRT display is also in the lab. Students can wave a bar magnet along the display to see the distortion
- Unless I get around to replacing the internal battery, the computer will beep twice and produce an error screen on boot (and the computer thinks it's January 01, 1900!). Jeff will (hopefully) remember to boot the computer before each lab
- Note for computer geeks: this is an IBM PS/Valuepoint 433DX/S, circa 1993 {Wikipedia page} that was used in our labs. It runs Windows 95, has 16 MB of RAM, a 200 MB hard drive, and Intel 486SX processor running at 33 MHz. Much less powerful than the phone in your pocket!
- A large horseshoe magnet is also in the lab. Students use this to check that their compass is pointing along the correct direction of B (out of north, into south), and to check the orientation of their bar magnet (the bump or white dot is North).
- The square coil (B around straight wire) and small vertical coil now have switches that easily allow the current to be reversed.
- Small vertical coil: The power supply is set to 3.0 volts DC. The switch is labeled Direct and Reverse. Students should use Direct first. The wires are color-coded (red and black) so that you can see the direction of current each way
- Square coil (straight wire): Set the knob on the green LabVolt power supply to '5' (the range switch is flipped up to Range A). A tap switch is labeled Direct and Reverse. Press and hold the Direct switch to send current down through the board holding the compasses. Press and hold the Reverse switch to change directions
- The horseshoe magnet is also used for the 'jumping wire' demo.
- Set the knob on the green LabVolt power supply to '5' or '6' (the range switch is flipped up to Range A)
- Lay the wire between the magnet poles (supported by the 4x4 wood block), and talk students through the right hand rule usage. Make sure the direction of I is such that F will point upwards initially
- Quickly press the tap switch. This momentarily shorts out the power supply. If the current is in the correct direction, the wire will fly out of the poles
- Ask students what will happen if the current is reversed. Use the right hand rule again to demonstrate, then loop the wire around so that I is in the opposite direction. The wire will attempt to move down through the wood block
- For some reason, students have difficulty understanding the point of Experiment 4, where they have to calculate the amount of current that needs to pass through the large solenoid to produce the same B as their bar magnet (I ≈ 15A) and the horseshoe magnet (I ≈ 50 - 75A). Holy current, Batman!
- The gaussmeter probe was broken during Spring 2023, so I gave them the 'actual' measurement of B for a bar magnet (40 mT), the horseshoe magnet (195 mT)and the solenoid (8 mT). Since the gaussmeter probe is fragile, and they really can't use it without assistance, I'll probably include these values in the directions going forward. The following is kept for historical significance
- Advise students about the correct use of the gaussmeter. It's very expensive (~$1k!), and the tip is fragile, so keep the plastic cover over the tip at all times. The meter should have been set for auto-range, and will measure the field on the order of mT. Make sure the flat part of the tip is perpendicular to the direction of B; this will give the maximum readout
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