180708: much of this prjt has to do with detecting small-ish fields as well and
getting some response from the field(s).
Don't forget that the field near the ground is 100v /meter.
180709: and don't forget 'static cling' and that additives exist to nullify it.
And Thompson discovered the e- with a vacuum chamber holding a horiz capacitor to
which was applied 'several thousand volts'
180410: thinking about making a BIG magnetic field using 2 circular, home-made magnets,
separated by ~ 1 foot. The diameter of the electromagnets should be about 8.84 inches,
giving an area of 1 over 2pi. No magical understanding here; just sounded cool. And
the choice of sizes is a tradeoff between cost, weight, easy of seeing effects on
statically charged (styrofoam) 'particles'.

This kind of magnet arrangement is called a
Helmholtz coil

mag gallery calculated plots of magnetic fields, 1 or more magnets visualizing fields with iron filings contained interesting images plus big excerpt from wikipedia on Magnetic Field. wiki/Inductor effects, equations of changing field or current. There are several magnet-related projects 'below' this project. This project serves as something of a collection point for procedures and terms. The terms, if generally useful, will naturally migrate further to glossary_sci.

name | len | dia | ohms | awg | notes |
---|---|---|---|---|---|

mag1 | _ | _ | 1.1 | 24 | _ |

mag2 | 1 15/16 | 1.25 | 9.66 | 24 | _ |

mag3 | 1.5" | 1.25 | 3.85 | 24 | _ |

Met math teach 'rebecca' at 2/6/16 robotics contest. Son 'Forrest' wants to stop a bullet w/ magnetism. (not a good choice). (deflect would even be tough). But I thought about lending him some magnets to 'play' with. And a video: (told mom he'd need a 'bench supply') 'electro magnets' {show permanent magnet electro magnet, spool, iron-ish core, pumpkin shape, compasses, filings on clear plastic surface above magnet(s), poles of a magnet, 'N' etc how to pick up filings, how to clean up (w/ bagged magnet), magnetizing something, hysteresis, bb's, nuts, Algebraically adding magnetic field strengths, superposition, coordinates. gluing perm mags to surface (hot glue, epoxy), 1/r2 (perpen to (invisible) field) VOM, induction, Faraday motors, solenoids, accelerating and decelerating projectiles. _deflecting_ projectiles. } No word from them. maybe too awkward.

- mag1. I don't remember which was #1 so I hereby assign the name to a long magnet wound on a wooden stick. The tape on it claims "1100 turns, 3 ohm resistance" (24 awg wire). Its timestamp reads "151030". The winding length is 26.25". The stick is about 1/4" in diameter.
- mag2. This magnet is longer than mag1 and is wound on a metal rod which looks like something from a BBQ. It has many more winds than mag1 and has a resistance of 3.4 ohms. The rod has some residual magnetization.
- mag3,4,5,6: 1.5" length, 1.25" dia. 3.9ohms. My goal with these was to make 4 identical magnets. These are wound on a bolt and the windings themselves are constained to 1.5 inches length and a 1.25 coil diameter. The short, stubby length was chosen to make them stronger (than a stretched out 'solenoid' type magnet). The bolts on these magnets also hold a residual field. These 4 magnets are generally kept in a small, semitranslucent box.
- prjt box(es): "magnetics", garage
- 4-5 large ring magnets.
- 20+ small ring magnets.

- smithsonian ceramic magnets.
- magnet wire, 3 1 lb spools, several smaller spools
- magnet wire, 2 1900ft spools, 1803xx

- measuring 'pull force'
- measuring the 'pull force'of a test magnet. ?? start w/ a weight (pennies? nickels?) known on a sensitive scale. make an air-core eMag w/ known dimensions, # of turns, wt, and current. attach to weight (by long string(?)), measure how much lighter the weight becomes due to a test magnet. can't let air-core touch the test magnet above it. measure distance. could change current. use bench supply. ?w/ resistor(?) Taking several readings at different currents could circumvent errors.
- guessimating nTurns
- as done for 'mag2'
The dims of the wound area was 1 15/16" (0.05m) long and had an OD of 1.5". The ID was approx 3/16". The wound dim in radial direction was (1.5-3/16)/2 = 0.56" A separate winding exercise showed about 72 windings/inch. That's 1"/72 windings = 0.0275" per winding. So how many windings would stack in 1 15/16" x 0.56"? 0.56" / 0.275 = 20 layers tall 1 15/16" / 0.275 = 70 turns in each layer. 20 x 70 = 1400 turns

If windings lay atop one another, they'd _mostly_ lie in the groove of the layer beneath - though they'd have to 'jump' to an adjacent groove to fit their direction of the helical turning. The wireCenter bottom winding to wireCenter above winding should a 60 degree angle. Sin(60) is .866 so the savings over having the wireCenters lie directly above one another would be 1-0.866 = 0.134 but mag2 windings have gaps in places so nTurns is probably lower. I've chosen to multiply by 1.125

1400 * 1.125 = 1575

mag2 { calc'g expected B0 = u0 N I / len_m u0 is 4pi * E-7 or 1.256e-6 N is nTurns // 1575 I is current in Amps = volts (16v)/ resistance (9.66) ohms) len_m is length of coil in meters. 0.05m 12.5 E-7 x 1575 x 1.6amps -------------------------- 0.05 meters coil length = 20 x 12.5 E-7 x 2520 = 250 E-7 x 2520 = 630000. E-7 = 0.063 T // ~1/16 Tesla * 10000 gauss/T = 63 gauss = 126 times SF's field

the following have moved to $pub/glossary_sci.html H field Henry inductance Km,relative magnetic permeability Lenz_Law Lorentz_Force Maxwell_3D paramagnetic e0, electric constant Q_factor rcTimeConstant relativitycalculator solenoid weber

- 24 gauge magnetic wire
1 ft == 0.3048m; 3.28 ft == 1 m 24awg copper. 0.0842 ohms/meter I expected this to be 24 wire diameters per inch but I get 72 turns/inch. Only curious so I can predict the needs of an electromagnet under design. POSSIBILITIES - the 'inch' isn't the length that matters. "centimeters" - it was spec'd as having a thicker covering and magnet wire has just the enamel.

- mag1
- 24 awg, 1.1 ohms. 13.06m (42.6')
- mag2
- 24 awg, 9.66 ohms. 114.7m 374')
- mag3
- 151008 mag3 is 1.5" long, not 1 15/16. but only 3.85 ohms! dunno why. was end of spool. dif thickness? short somewhere ?(doubt it. pretty tough stuff).
- spinner
- rotatable globe or the like, suspended/supported by mag fields. field changes cause spin.
- train
- a simple train 'car' (mechanically?) constrained to float above a 'track'. Ideal would be to shape fields to constrain its position.