Summary

{{Information

|Description=

|Source=Own work |Author=Geek3 |Date=2010-10 |other_versions=* VFPt dipole animation electric.gif

• VFPt dipole animation magnetic.gif

|Other fields={{Igen|VectorFieldPlot|n|+|c1=

mkdir anims
./vectorfieldplot.py

1. paste this code at the end of VectorFieldPlot 1.2

frames = 100 d = 0.35 # animation amplitude r = 7.5 # charge radius

1. iterate frames

for i in range(frames):

   doc = FieldplotDocument('VFPt_dipole_animation_{0:0>2}'.format(i),
       commons=True, width=220, height=220, unit=100)
   a = abs(sin(i*2*pi/frames) * 0.75 - 0.25 * sin(3.0 * i*2*pi/frames))
   
   if i == 0 or i == frames / 2:
       # pointlike dipole
       field = Field({'dipoles':0,0,1,0})
   elif i < frames / 2:
       # electric dipole
       field = Field({'monopoles':[[-d*a,0,-0.5/(d*a)], [d*a,0,0.5/(d*a)]]})
       doc.draw_charges(field, scale=r/14)
   else:
       # magnetic dipole
       field = Field({'ringcurrents':0,0,0,d*a,1})
       doc.draw_currents(field, scale=r/14)
   if d * a < r / doc.unit:
       # draw dipole symbol
       symb = doc.draw_object('g', {'id':'dipole_symbol', 
           'transform':'scale({0},{0})'.format(
           sqrt(1.0/doc.unit**2-(d*a/r)**2))})
       defs = doc.draw_object('defs', {}, group=symb)
       spot = doc.draw_object('radialGradient', {'id':'light_spot',
           'cx':'0.65', 'cy':'0.7', 'r':'0.75'}, group=defs)
       for col, of in [['#fff', '0'], ['#ddd', '0.15'],
                       ['#aaa', '0.7'], ['#444', '1']]:
           doc.draw_object('stop', {'stop-color':col, 'offset':of}, group=spot)
       doc.draw_object('circle', {'cx':'0', 'cy':'0', 'r':str(r),
           'style':'fill:url(#light_spot); stroke:#000000; stroke-width:1'}, group=symb)
       doc.draw_object('path', {'style':'fill:#000000; stroke:none',
           'd':'M -4,1 H 0 V 4 L 5,0 L 0,-4 V -1 H -4 V 1 Z'}, group=symb)
   
   n = 20
   # iterate fieldlines
   for j in range(n):
       t = -1.0 + 2.0 * (j + 0.5) / n
       y = 0.25 * ((t-1)**-2 - (t+1)**-2) - 0.3*t
       dy = 0.0
       sf = None
       if i > frames / 2:
           dy = (y / abs(y) * d * a) * (1.0 - t**2)
           sf = [lambda p:-p[0], lambda p:p[0]]
       line = FieldLine(field, [0, y + dy],
           directions='both', maxr=1e4, maxn=2e4,
           stop_funcs=sf)
       doc.draw_line(line, linewidth=1.0,
           arrows_style={'dist':1.25, 'scale':1.1, 'max_arrows':2})
   
   doc.write(filename='anims/' + doc.name)

}} }}

for i in anims/*.svg; do rsvg -w1760 -h1760 $i $(echo $i | sed s/svg/png/) && convert -scale 220x220 $(echo $i | sed s/svg/png/) $(echo $i | sed s/svg/gif/); done
gifsicle -d5 -l0 --colors 256 --comment "http://commons.wikimedia.org/wiki/File:VFPt_dipole_animation.gif" anims/*.gif > VFPt_dipole_animation.gif

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