Exercises with Magnetic Monopoles - Kurt Nalty
Exercises with Magnetic Monopoles - Kurt Nalty
Exercises with Magnetic Monopoles - Kurt Nalty
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Field Angular Momentum due to Charge/Monopole<br />
Interaction<br />
This section follows homework problem 8, chapter 3 of Julian Schwinger’s<br />
Classical Electrodynamics. Place an electric charge at (0, 0, R/2). Place a<br />
magnetic charge at (0, 0, −R/2).<br />
The electric field is<br />
⎡ ⎛<br />
⎤<br />
⃗E(x, y, z) = q e<br />
4πɛ<br />
⎞<br />
⎣−∇<br />
⃗ ⎝<br />
1<br />
√<br />
⎠⎦<br />
x 2 + y 2 + (z − R/2) 2<br />
= q e x⃗a x + y⃗a y + (z − R/2)⃗a z<br />
4πɛ<br />
(<br />
x2 + y 2 + (z − R/2) 2) 3/2<br />
The magnetic field is<br />
⃗B(x, y, z) = µq m<br />
4π<br />
= µq m<br />
4π<br />
The power flux Poynting vector is<br />
⃗S = 1 µ ( ⃗ E × ⃗ B)<br />
⎡ ⎛<br />
⎞⎤<br />
⎣−∇<br />
⃗ ⎝<br />
1<br />
√<br />
⎠⎦<br />
x 2 + y 2 + (z + R/2) 2<br />
x⃗a x + y⃗a y + (z + R/2)⃗a z<br />
(<br />
x2 + y 2 + (z + R/2) 2) 3/2<br />
= 1 q e x⃗a x + y⃗a y + (z − R/2)⃗a z<br />
µ 4πɛ<br />
(<br />
x2 + y 2 + (z − R/2) 2) × µq m x⃗a x + y⃗a y + (z + R/2)⃗a z<br />
3/2<br />
4π<br />
(<br />
x2 + y 2 + (z + R/2) 2) 3/2<br />
= q eq m 1<br />
yR⃗a x − xR⃗a y<br />
16π 2 ɛ<br />
(<br />
x2 + y 2 + (z − R/2) 2) 3/2 (<br />
x2 + y 2 + (z + R/2) 2) 3/2<br />
The momentum density is<br />
ɛµ ⃗ S = µq eq m<br />
16π 2<br />
yR⃗a x − xR⃗a y<br />
(<br />
x2 + y 2 + (z − R/2) 2) 3/2 (<br />
x2 + y 2 + (z + R/2) 2) 3/2<br />
3