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Pepealej
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Homework Statement
Inside a very long, straight and hollow plastic tube (R << L) we have ionized liquid moving at a velocity v = 100 m/s. The net charge per unit volume is n = 106 electrons/m3. The radius of the tube is R = 10cm. Around the tube we have a solenoid, with n = 100 loops/m, through which circulates a current I = 2 A.
Estimate the magnetic field on the axis of the tube at a distance d >> L.
Book's answer
0 T or, considering the system as a dipole, [tex]B=\dfrac{\mu_0}{2\pi d^3}N\pi r^2[/tex]
My question
I understand how the magnetic field is 0 T but, how can I consider the system as a dipole to obtain the other answer?
Thanks in advance!
Inside a very long, straight and hollow plastic tube (R << L) we have ionized liquid moving at a velocity v = 100 m/s. The net charge per unit volume is n = 106 electrons/m3. The radius of the tube is R = 10cm. Around the tube we have a solenoid, with n = 100 loops/m, through which circulates a current I = 2 A.
Estimate the magnetic field on the axis of the tube at a distance d >> L.
Book's answer
0 T or, considering the system as a dipole, [tex]B=\dfrac{\mu_0}{2\pi d^3}N\pi r^2[/tex]
My question
I understand how the magnetic field is 0 T but, how can I consider the system as a dipole to obtain the other answer?
Thanks in advance!
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