Summary

{{Information

|description=

|date=2018-07-14 |source=Own work |author=Geek3 |permission=

|other versions=

|other fields={{Igen|VectorFieldPlot|0|+|s1=Python VectorFieldPlot code|c1=

1. paste this code at the end of VectorFieldPlot 1.8

doc = FieldplotDocument('VFPt_sphere-magnet-Sup', commons=True,

   width=600, height=600)

x0, y0 = 0.0, 0.0 R = 1.0

def spheremagnet_field(xy):

   p = sc.array((0., -1.))
   r = xy - sc.array((x0, y0))
   d = vabs(r)
   if d < R:
       # inside the field is indeed constant
       Fxy = p / (2. * pi * R**3)
   else:
       # outside the field is exatly that of a point-dipole
       Fxy = (3. * sc.dot(p, r) * r - sc.dot(r, r) * p) / (4.*pi*d**5)
   return Fxy

field = Field({'custom':[spheremagnet_field]})

n = 20 for i in range(n):

   p0 = (R * (2 * (i + 0.5) / n - 1), 0.)
   line = FieldLine(field, p0, directions='both', maxr=7)
   doc.draw_line(line, arrows_style={'dist':2.0,
       'max_arrows':2, 'offsets':[0.9, 0.3, 0.3, 0.9], 'scale':1.25})

1. draw the spherical magnet

g = doc.draw_object('g', {'id':'sphere',

   'transform':'translate({},{})'.format(x0, y0)})

defs = doc.draw_object('defs', {}, group=g) grad = doc.draw_object('radialGradient', {'id':'grad', 'r':str(1.2*R),

   'cx':'0', 'cy':str(0.2*R), 'fx':'0', 'fy':str(0.6*R),
   'gradientUnits':'userSpaceOnUse'}, group=defs)

for col, of, opa in [['#ffffff', '0', '0.7'], ['#ffffff', '0.04', '0.6'],

       ['#ffffff', '0.11', '0.4'], ['#ffffff', '0.22', '0.2'],
       ['#555555', '0.7', '0.3'], ['#000000', '1', '0.6']]:
   stop = doc.draw_object('stop', {'stop-color':col, 'offset':of,
       'stop-opacity':opa}, group=grad)

clip = doc.draw_object('clipPath', {'id':'circle_clip'}, group=defs) doc.draw_object('circle', {'cx':'0', 'cy':'0', 'r':str(R)}, group=clip)

gc = doc.draw_object('g', {'clip-path':'url(#circle_clip)'}, group=g) doc.draw_object('circle', {'cx':'0', 'cy':'0', 'r':str(R),

   'style':'fill:#ff0000; stroke:none;'}, group=gc)

doc.draw_object('path', {'d':'M -1,0 A 1,1 0 0 0 1,0 L -1,0 Z',

   'style':'fill:#00cc00; stroke:none;'}, group=gc)

text_S = doc.draw_object('text', {'text-anchor':'middle', 'x':'0', 'y':'0',

   'transform':'translate({},{}) scale({},{})'.format(0, 0.56*R-0.2, 0.05, -0.05),
   'style':'fill:#000000; stroke:none; ' +
   'font-size:12px; font-family:Bitstream Vera Sans;'}, group=g)

text_S.text = 'S' text_N = doc.draw_object('text', {'text-anchor':'middle', 'x':'0', 'y':'0',

   'transform':'translate({},{}) scale({},{})'.format(0, -0.56*R-0.2, 0.05, -0.05),
   'style':'fill:#000000; stroke:none; ' +
   'font-size:12px; font-family:Bitstream Vera Sans;'}, group=g)

text_N.text = 'N' doc.draw_object('circle', {'cx':'0', 'cy':'0', 'r':str(R),

   'style':'fill:url(#grad); stroke:none;',
   'transform':'rotate(30) scale(1.4,1)'}, group=gc)

doc.draw_object('circle', {'cx':'0', 'cy':'0', 'r':str(R),

    'style':'fill:none; stroke:#000000; stroke-width:0.04;'}, group=g)

doc.write() }} }}

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