162 Magnetic FieldsQ29.7Since FvBBq=×af, then the acceleration produced by a magnetic field on a particle of mass misavBBqm. For the acceleration to change the speed, a component of the acceleration must be inthe direction of the velocity. The cross product tells us that the acceleration must be perpendicular tothe velocity, and thus can only change the direction of the velocity.Q29.8The magnetic field in a cyclotron essentially keeps the charged particle in the electric field for alonger period of time, and thus experiencing a larger change in speed from the electric field, byforcing it in a spiral path. Without the magnetic field, the particle would have to move in a straightline through an electric field over a distance that is very large compared to the size of the cyclotron.Q29.9(a)The qvB×force on each electron is down. Since electrons are negative, ×must be up.With vto the right, Bmust be into the page, away from you.
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This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .