File:VFPt sphere-magnet potential.svg
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Size of this PNG preview of this SVG file: 600 × 600 pixels. Other resolutions: 240 × 240 pixels | 480 × 480 pixels | 768 × 768 pixels | 1,024 × 1,024 pixels | 2,048 × 2,048 pixels.
Original file (SVG file, nominally 600 × 600 pixels, file size: 90 KB)
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Summary[edit]
| Description |
English: Drawing of a homogeneously magnetized spherical magnet with exactly computed magnetic field lines. A spherical magnet has the remarkable property that its field outside the magnet is identical to that of an ideal point-like dipole. Inside the magnetized volume, the field is exactly constant and aligned along the north-south axis. The magnetic scalar potential 𝜓 is shown in the background from positive (fuchsia) through zero (yellow) to negative (aqua). Note that the field lines follow the gradient of the scalar potential. |
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| Date | |||
| Source | Own work | ||
| Author | Geek3 | ||
| Other versions |
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| SVG development |  This W3C-invalid vector image was created with Inkscape, or with something else.
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| Source code | SVG code# paste this code at the end of VectorFieldPlot 2.2
doc = FieldplotDocument('VFPt_sphere-magnet_potential', commons=True,
width=600, height=600)
R = 1.0
c = sc.array([0., 0.])
M = sc.array([0., 1.])
field_outside = Field([ ['dipole', {'x':c[0], 'y':c[1], 'px':M[0]*4./3.*pi*R**3, 'py':M[1]*4./3.*pi*R**3}] ])
Bfield_inside = Field([ ['homogeneous', {'Fx':2./3.*M[0], 'Fy':2./3.*M[1]}] ])
Hfield_inside = Field([ ['homogeneous', {'Fx':-1/3.*M[0], 'Fy':-1/3.*M[1]}] ])
def spheremagnet_Bfield(xy):
if vabs(xy - c) < R:
return Bfield_inside.F(xy)
else:
return field_outside.F(xy)
def spheremagnet_potential(xy):
if vabs(xy - c) < R:
return Hfield_inside.V(xy)
else:
return field_outside.V(xy)
field = Field([ ['custom', {'F':spheremagnet_Bfield, 'V':spheremagnet_potential}] ])
U0 = field.V(c + R * vnorm(M))
doc.draw_scalar_field(func=field.V, cmap=doc.cmap_AqYlFs, vmin=-U0, vmax=U0)
nlines = 20
for iline in range(nlines):
p0 = (R * (2 * (iline + 0.5) / nlines - 1), 0.)
line = FieldLine(field, p0, directions='both', maxr=7)
if fabs(iline - (nlines - 1) / 2.) < 1.:
of = 0.2
elif fabs(iline - (nlines - 1) / 2.) < 2.:
of = 0.23
elif fabs(iline - (nlines - 1) / 2.) < 3.:
of = 0.3
elif fabs(iline - (nlines - 1) / 2.) < 4.:
of = 0.53
elif fabs(iline - (nlines - 1) / 2.) < 5.:
of = 0.4
elif fabs(iline - (nlines - 1) / 2.) < 6.:
of = 0.38
else:
of = 0.3
off = {'start':0.9, 'leave_image':of, 'enter_image':of, 'end':0.9}
doc.draw_line(line, arrows_style={'dist':2.0,
'max_arrows':2, 'offsets':off})
# draw the spherical magnet
g = doc.draw_object('g', {'id':'sphere',
'transform':'translate({},{})'.format(*c)})
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', '0.8'], ['#ffffff', '0.04', '0.7'],
['#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:#00cc00; 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:#ff0000; stroke:none;'}, group=gc)
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'
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'
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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Licensing[edit]
I, the copyright holder of this work, hereby publish it under the following license:
This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.
- You are free:
- to share – to copy, distribute and transmit the work
- to remix – to adapt the work
- Under the following conditions:
- attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
- share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
|---|---|---|---|---|---|
| current | 10:55, 22 September 2019 | | 600 × 600 (90 KB) | Geek3 (talk | contribs) | User created page with UploadWizard |
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