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Physics 2213 HW #11 — Solutions
Fall 2008
27.19
[Fusion Reactor]
In part (a), apply conservation of energy to the motion of the two nuclei. In part (b) apply
In part (a), let point 1 be when the two nuclei are far apart and let point 2 be when they are at their
closest separation.
(a)
.
so
and
.
(b)
gives
.
.
The speed calculated in part (a) is large, 4% of the speed of light, but still small enough to justify the use
of nonrelativistic formulas with a reasonable precision.
27.22
[Cosmic Ray Experiment]
For motion in an arc of a circle,
and the net force is radially inward, toward the center of the circle.
The direction of the force is shown in the figure to the right. The mass of a proton is
.
(a)
is opposite to the righthand rule direction, so the charge is negative.
gives
.
and
.
(b)
.
. The magnetic force is much larger than the weight of the
particle, so it is a very good approximation to neglect gravity.
(c)
The magnetic force is always perpendicular to the path and does no work. The particles move with
constant speed.
27.60
[TV Picture Tube]
Apply
. Assume
(a)
The path is sketched in the figure to the right.
(b)
Motion is circular:
(path of deflected
particle)
(equation for tangent to the circle, path of undeflected particle).
. If
,
. For a particle moving in a magnetic field,
But
Thus, the deflection
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(c)
which is fairly significant.
Note: In part (c),
and
, so the approximation in part (b) is valid.
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 Fall '07
 PERELSTEIN,M
 Electron, Magnetism, Conservation Of Energy, Energy, Force, Heat, Magnetic Force, Magnetic Field, Electric charge

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