1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
|
from visual import *
print """
Drag or click to show the magnetic field interactively.
Mark the magnetic field vector at the end of the drag.
"""
scene.width = 600
scene.height = 600
Rbig = 0.6
L = 2*pi*Rbig
Rsmall = 0.2
k = 1E-7 # mu-zero/4pi
I = 1.0
Ncoils = 20
Bscale = (2.*Rsmall)/(4*pi*1E-7*Ncoils*I/L)
dphi = 2.*pi/Ncoils/15.
phi = arange(0,2*pi+dphi,dphi)
helix=curve(x = Rbig*cos(phi)+Rsmall*cos(Ncoils*phi)*cos(phi),
y = Rbig*sin(phi)+Rsmall*cos(Ncoils*phi)*sin(phi),
z = -Rsmall*sin(Ncoils*phi))
helix.color = (1,0.7,0.2)
helix.radius = 0.01
delta = helix.pos[1:] - helix.pos[:-1]
center = (helix.pos[:-1] + helix.pos[1:])/2.
scene.range = 1.3*(Rbig+Rsmall)
vwidth = L/100
def BField(obs):
r = obs-center
rmag = mag(r)
rmag.shape = (-1,1)
return sum(k*I*cross(delta, r)/rmag**3)
Bvector = arrow(axis=(0,0,0), shaftwidth=vwidth, color=(0,1,1))
drag = 0
while 1:
if drag:
newobs = scene.mouse.pos
if newobs != obs:
obs = newobs
Bvector.axis = Bscale*BField(obs)
Bvector.pos = obs
if scene.mouse.events:
m = scene.mouse.getevent()
if m.drag:
drag = 1
obs = None # force update of position
scene.cursor.visible = 0
if m.drop:
drag = 0
scene.cursor.visible = 1
arrow(pos=obs, axis=Bscale*BField(obs), shaftwidth=vwidth, color=(0,1,1))
elif m.click:
arrow(pos=m.pos, axis=Bscale*BField(m.pos), shaftwidth=vwidth, color=(0,1,1))
|
