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1- An electron lies at rest in the magnetic field of an infinite straight
wire carrying a current I. At t=0, the wire is suddenly charged to a
positive potential V0 without affecting I. The electron gains energy
from the electric field and begins to drift. Draw a diagram showing
the orbit of the electron and relative direction of I, B, VE, Vgard B,
and VR . (20)
-
Rc
B
B
VE
VB
E
VR
I
wire
+
VR
E
B
VB
Rc
VE
X
-
Reactor Wall
2- A 5-KeV H+ in a large mirror fusion device has a pinch angle Θ of
45 degrees at the midplane, where B=0.7 T. Determine its Larmor
radius. (10)
1
mV 2
2
mV
rLarmor 
eBmax
E
sin 2 () 
Bmin
Bmax
rLarmor 
2mE sin 2 ()
 0.0073
q  Bmin
[ m]
3- A HeIII make 1000 revolutions while moving 1 cm perpendicular to
an electric and magnetic field, which are in turn, perpendicular to
each other. How strong is the magnetic induction B when E is equal
to 10 V/m. (20)
 d
  qB  E
VE     g   is tan ce   

 nrevolution   2m  B
B
2mEN revolution
 0.3608
qd is tan ce
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