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• fieldDraw.py
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• python
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Project Overview

This looks like a complex and physically dangerous area. Some of the efforts will be simply rubbing together things which make small amounts of static electricity (see triboelectric).

Guidance from the involved units:

N	=	Force, 'Coulombic force'. Output from Coulomb's eqn
N/C	=	Electric Field (strength), 'E field', 'E'; (= V/m), spatial density
V	=	Voltage, 'potential' = J/C = N•m/C; 1/r calc; (Energy per C)
J	=	PE: W=VQ, total PE of charges in Q (XAM p78.7)

Small projects related to the E field topic. Explained in sections below.

1. draw E fields	calculate and display E field vectors or contours, Win10, py
2. emit negative ions	actually make electrons in a non-vacuum environment.
3. voltage multiplier	CCW, "Cockcroft-Walton" voltage multiplier (section below).
4. electrometer	Measure the strength of weak E-fields. Try using oscilloscope too.
5. make capacitators	get the hang of plate separation, dielectrics etc.
6. measure emitters	with Junior Theremins. Record events on video.

Interactions with magnetic fields will be handled by the magnetics prjt or one of its component projects.

Links and vocab will collect here, at least temporarily. Most will migrate to glossary_sci.html (aka 'gsci').

See section on 'atmospherics' below.

Editing methods

The real code file is edited in python IDE. It proved risky to have 2 editors active.
files 'review*.txt' are displayed in sep windows, side by side.
advice: when saving interesting results, merge review files and rename w/ 8 digit date.

eFields.tws	p/eFields/	reviewCode.txt,define_,todo_,html files
_eFields.tws	Python34/examples/	reviewOuts.txt, (fieldDraw.py if no py IDE running)   edits copies of eFields.tws files. for L-R code moves
_fieldAssist.tws	Python34/examples/	bounce1.py, _unitNotes.txt, gsci, bounce   function() snippets (docdoc.txt)
_field.tws	Python34/examples/	temporary. don't expect this to exist long...   helpful py files (bounce, graf, egList...)

Testing methods

Overview:

1. find a new or illustrative example problem containing a known solution.
2. code it up as a challenge to the efield python software.
3. wrap this new test case as a function and add that function to the list of functions
4. (re)run the test program and check to see that the new test case passes.

Specifics:
The test code source files are Python34/examples/fieldTest*.py' $p/eFields/test_eFields.txt

prjt:1 modeling program, 'fieldDraw'

Be sure to understand this electric_field, gsci
Notes on the program's devt.:
# the grid is optionally computed and drawn. The only reason not to
# draw it is to see the charges' acceleration and velocity vectors -
# which is not going into the 1st pass of this model (180725)
gridScale, dist between points.
gridDelX, DelY
eFld[ ]      x,y's for field arrow at this point
grid[ ] [ ]  has .x  .y  ?total length?

Drawing =================================================
The Charges gets drawn as little circles, dif colors for +,-
The field exactly at a charge is perpendicular to the page!
The field drawing only makes sense at 'grid' points which don't
match charge positions.
Field is an arrow, arrowLen

optimizations, improvements, damned ideas! ==============
Any way to only (re)calc what needs calculating? yawn...

prjt:2 negative Ion generator

Bought a neg Ion generator and have only sketchy plans for it. Move dust across office(?). Make a ground or positive plate a distance away(?)

Does this make ozone?
Would this draw particulates to a surface which could be cleaned easily.
Would the plasma ball (globe) also do this?

prjt:3 Cockcroft-Walton voltage multiplier

CCW, gsci

prjt:4 detecting small fields, electroscope?

Popular Electronics, June 1968 popElectronics68/*.jpg

prjt:5 detecting tiny fields, using an electrometer

This prjt looks so complicated that it's given it's own project

prjt:7 home made capacitors

physical mount: Talenti ice cream jars. 1 pint, 2 pint
outer plate choices:
    0.025" aluminum sheeting. ouch! expensive. Home Depot
    steel soup can split and wrapped around the 1 pint jar(s). 'wavey'
    aluminum foil, kitchen variety. wrapped several (4-5?) times.
inner plate choices:
    0.025" aluminum sheeting. coiled up. 3.25" or 2.75" wide
    1/4" x ~4" long screw approximately centered in jar, held by top.
   "tube" was a 7/8" diameter x ~4" alum tube, centered in jar, held by top
    steel soup can used as inner plate on one of the 2pint jars. "small can"
dielectrics
    air, distilled water, paraffin
measurements made with my best VOM (Extech).

'dielectric' in gsci

Flat plate capacitor, 6" x 23 7/8" x  1/4" aluminum sheets. Extech VOM
    0.608 nF held apart with 3 tie wraps, spread out, 1 layer as thick as 1 tie wrap.
    0.316 nF 2 layers of same tie wraps. separation ~ 0.1" # used 6 ties, crossed in 4 places.
    3.24x nF single sheets of paper both separation and (?) dielectric
    Cap equation, gsci gives "C = eR * e0 * Area / separation"
    (area of plates=='A') = 6"x23.875" = .153m * .609m = 0.093m²
    C = eR * e0 * A / (separation=='d_m')
    d_m = eR * (e0=8.854187¤-12 F/m) * (A=0.093m²) / (C=3.24e-9F)
    # eR is the dielectric constant, aka 'relative permittivity'. so treating as 1. 
    d_m = (eR=1) * (e0=8.854¤-12 F/m) * (A=0.093m²) / (C=3.24e-9F)
    d_m = 2.54e-4 m; d_in = .00997" => piece of paper is 1/100" thick. wrong. 500shts=2" so paper is .004" / sheet
    # could correct by assuming eR = 0.4 # so d_m would be ~ 1.0e-4 and d_in ~ .004"
    # but (practical) dielectric constants need to be > 1
    # paper dielectric == 2.3; do I have an eqn upside down? Off a digit? 
    d_m = (eR=2.3) * (e0=8.854¤-12 F/m) * (A=0.093m²) / (C=3.24e-9F)
    d_m = 5.81e-4 m = .0227"  # that's worse. ~44 shts per inch, not 250.
    1/2.3 = .435 is just about the number need (ideally 0.4)


Observations:
Capacitance values are small! well less than 1 nF (nano-Farad)
When 2 homemade caps wired in parallel, values summed so they act like caps.
Grabbing outside with your hand added to measured capacitance value.
Sliding the central 7/8" tube out most of its length only reduced C _some_ !
The jar w/ wavy steel sides was signif lower C than one w/ solid alum.
I hoped to charge caps w/ battery then measure voltage w/ VOM. didnt work
The paraffin reading, jar 6. Expected much higher. 0.037 is like air!
    'paraffin' defines a wide range of hydrocarbons. Maybe my Safeway paraffin is weird.
     Actually, 'like air' is generous. The VOM measures 0.031 when the leads
     are not connected to anything (maybe it measured me b/c I was holding leads).
When I used the VOM to measure the C for my body, the value kept climbing and
    pretty quickly at that. Was the VOM charging my body? Detectable result?

Questions:
May have to re-measure. My body should not be part of the measurement.
Commercial caps cite a voltage value as well as capacitance. What would be the V for these?
Shouldn't the water to air ratio for jar caps should be constant? (ratio of dielectrics...)
Could I duplicate a 'jar cap' design and get close to the same answer?
Why doesn't distilled water show a dielectric nearer to 80, as mentioned in wikip?
    My distilled is not pure (?). Got it from Sprouts store, near by.
Is the C fm bigger jars 'worth it' ? (think not. none of these C's are really usable...)
If I use one of these caps in a tuned circuit, does the resonant freq match values here?
Why do C values drift upwards (a bit) during some of the measurements?

possible follow-ons:  
    take, add a row of photos of the jars etc.
    run function gen square wave thru 2n2222 and caps. observe w/ 'scope, VOM A/C
    try a mineral oil dielectric?
    add measurement column for hand touching outer sheet?
    Apply the capacitor eqn to the flat plate cap. Reasonable answer?

prjt Make high capacitance electrolytic

rimstarorg { I like should be accessible thru
    http://youtube.com/rimstarorg
    made 37uF electrolytic cap. alum foil, paper towels,
    homemade liquid on paper towels.
    distilled water + sodium bicarbonate, baking soda
}

prjt:6 Detecting, measuring transient E-field events

Jr Theremins(?), oscilloscope(?)

Atmospherics

Consider: E _IS_ _charge_
atmosphere ~30 miles thick, 300kV dif. = 10kV/mile = 2v/foot avg.
from https://en.wikipedia.org/wiki/Atmospheric_electricity {
The air above the surface of Earth is positively charged, while the Earth's surface charge is negative.

Because the atmospheric electric field is negatively directed in fair weather, the convention is
to refer to the potential gradient, which has the opposite sign and is about 100V/m at the surface.

There is a weak conduction current of atmospheric ions moving in the atmospheric electric field,
about 2 picoAmperes per square metre, and the air is weakly conductive due to the presence of
these atmospheric ions. (2e¤-12amps * 6.24¤18chgs/Coulomb * 1Coulomb/amp-sec) = 12¤6 particles/sec/sqMeter
}
TreshaEdwards.shtml {
    'directed inward'. => positive up high, neg at earth's surface (?)
    'at surface 66 N/C to 150 N/C. 150 more real'
    'intensity decreases w/ altitude' (gradient(?))
    '120 V/m at surface','exponential increase in conductivity w/ altitude'.
    'at 30km alt, field as low as 300 mV/m'
    'thunderstorms  field, usually reversing polarity under cloud'
    'max current, world-wide, occurs at 1900 UTC'
    }
    Atmos eFld {
    '100V/m near surface' 'polarity: drives + chg downwards'
    'polution affects chg distribution'
    }
    why it doesn't shock you as is.
what is lightning (incl numbers, speed, rate), how's it form.
what about familiar static shock (numbers). relationship to humidity.
VDG vandegraff generator. use, risk, numbers.
corona discharge.
means of measuring
    electroscope.
    meters
wiki,Capacitor
instructables, DIY-Capacitor
hi voltage cap using lg pop bottle, water, alum foil as means of generating static charge.

Project needs or uses

tech tools: electrometer 3B, VOM,

Procedures

safety.  gloves, safety signs, VDG discharging, cat safety.

Glossary

Lessons Learned

A little (more) design time would have saved a lot of time fiddling with code. I really launched into coding w/o a solid understanding of the material. The good news was that I set up a test environment very early. My central problem was figuring out which aspects were vectors, which just scalars.

Related Files, Web pages