Deflection of an Electron in a Magnetic Field
Deflection of an Electron in a Magnetic Field
Deflection of an Electron in a Magnetic Field
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magnetic field that is generated by a current-carry<strong>in</strong>g wire. In this setup, the electron is<br />
mov<strong>in</strong>g perpendicular to the magnetic field. Thus, the force on the electron is:<br />
F = evB (3)<br />
Additionally, we know from last semester that, when the force act<strong>in</strong>g on a body is<br />
perpendicular to the motion, the result<strong>in</strong>g motion is circular. Us<strong>in</strong>g this <strong>an</strong>d conservation<br />
<strong>of</strong> energy SHOW that the electrons<br />
!<br />
will move <strong>in</strong> a circle <strong>of</strong> radius R, given <strong>in</strong> equation 4:<br />
R = m eB<br />
2eV acc<br />
m<br />
(4)<br />
The radius <strong>of</strong> curvature is related to the spot that is made on the screen, as seen <strong>in</strong><br />
Figure 2. The electron beam is travel<strong>in</strong>g from the left (where it is emitted by the electron<br />
gun) to the <strong>an</strong>ode, <strong>an</strong>d then ! on towards the screen. In the absence <strong>of</strong> a magnetic field this<br />
trajectory would be a straight l<strong>in</strong>e path, a dist<strong>an</strong>ce S long; however, when a magnetic<br />
field is added (<strong>in</strong>to the page) the electron beam will curve away from its orig<strong>in</strong>al course,<br />
as seen <strong>in</strong> Figure 1.<br />
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