A trip through magnetic fields
A positively charged particle, which was initially moving in the
direction on the
-plane, passes through points
P
,
Q
and
R
, as shown above. The magnetic field intensities of area
I
and area
II
are
and
respectively, and
P
and
Q
have the same distance from the origin
O
. If it takes
for the charged particle to move from
P
to
Q
, how long will it take for it to move from
Q
to
R
?
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Radius, R of the trajectory (circle) of a charged particle, (m,q) moving with speed v in magnetic field, B is given by R = q B m v . From this we can see that OQ is half the radius of the original arc QR. Thus the particle traverses an angle of π / 3 about the center of revolution. Also the time period of circular motion is given by T = q B 2 π m . Combine the two to get 3 4 T