File:VFPt magnet B.svg
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Original file (SVG file, nominally 400 × 300 pixels, file size: 30 KB)
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Summary
| Description |
English: Magnetic B-field inside and outside of a cylindrical bar magnet. The field is accurately computed with a physical model. Discrete field lines are drawn. |
| Date | |
| Source | Own work |
| Author | Geek3 |
| Other versions |
 with electric current symbols |
| SVG development |  This plot was created with VectorFieldPlot. |
| Source code | Python code# paste this code at the end of VectorFieldPlot 1.4
import scipy.optimize as op
M = 1.0 # magnetic moment
r = 0.65; l = 1.2
n = 10
fieldB = Field({'coils':[[0, 0, 0, r, l, M/(r**2*pi)]]})
fieldH = Field({'charged_discs':[[-l, -r, -l, r, -0.5*M/l],
[ l, -r, l, r, 0.5*M/l]]})
inside = lambda p: -min(1-fabs(p[0]/l), 1-fabs(p[1]/r))
outside = lambda p: min(1-fabs(p[0]/l), 1-fabs(p[1]/r))
for field in ['B', 'H']:
fname = 'VFPt_magnet_' + field
doc = FieldplotDocument(fname, width=400, height=300, commons=True)
for i in range(n):
r_rel = 2 * (0.5 + i) / n - 1
y0 = r * (r_rel + 0.16 * (r_rel - r_rel**3))
p0 = sc.array([l, y0])
line1 = FieldLine(fieldB, p0*(1+1e-9), directions='forward',
maxr=1e4, maxn=1e4, stop_funcs=2*[outside])
doc.draw_line(line1, arrows_style={})
# B-field inside magnet
line2 = FieldLine(fieldB, p0*(1-1e-9), directions='backward',
stop_funcs=2*[inside])
if field == 'B':
doc.draw_line(line2, arrows_style={})
# H-field inside magnet
line3 = FieldLine(fieldH, p0*(1-1e-9), directions='forward',
stop_funcs=2*[inside])
if field == 'H':
doc.draw_line(line3, arrows_style={
'min_arrows':0, 'dist':0.6, 'max_arrows':2})
p1 = line3.nodes[-1]['p'] # where lines leave the magnet on the side
if fabs(p1[1]) >= r * (1-1e-8):
p1[1] = copysign(max(r, fabs(p1[1])), p1[1])
line4 = FieldLine(fieldH, p1, directions='forward',
stop_funcs=2*[outside])
doc.draw_line(line4, arrows_style={'max_arrows':2})
p2 = line4.nodes[-1]['p'] # where lines re-enter the magnet
line5 = FieldLine(fieldH, p2, directions='forward',
stop_funcs=2*[inside])
if field == 'H':
doc.draw_line(line5, arrows_style={
'min_arrows':0, 'dist':0.6, 'max_arrows':2})
line6 = FieldLine(fieldB, p1*(1-1e-9), directions='backward',
stop_funcs=2*[inside])
if field == 'B':
doc.draw_line(line6, arrows_style={})
if field == 'H':
doc.draw_object('path', {'d':'M {},{} V {} M {},{} V {}'.format(
-l, -r, r, l, -r, r), 'style':'stroke:#999999; stroke-width:0.02'})
doc.draw_magnets(fieldB)
# postprocessing: strip text and add opacity
for el in doc.svg.iter():
if el.tag.endswith('g'):
if el.get('id') != None and 'magnet' in el.get('id'):
el.set('opacity', '0.4')
if el.tag.endswith('text'):
el.getparent().remove(el)
doc.write()
|
Licensing
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.
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File history
Click on a date/time to view the file as it appeared at that time.
| Date/Time | Thumbnail | Dimensions | User | Comment | |
|---|---|---|---|---|---|
| current | 13:25, 1 May 2017 | | 400 × 300 (30 KB) | Geek3 | User created page with UploadWizard |
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