Physics: Principles with Applications (7th Edition)

Published by Pearson
ISBN 10: 0-32162-592-7
ISBN 13: 978-0-32162-592-2

Chapter 20 - Magnetism - Search and Learn - Page 589: 2

Answer

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Work Step by Step

a. F=qE. The electron, which has negative charge, accelerates in a direction opposite to that of the electric field. For the electron to accelerate east, the electric field is directed to the west. b. The electron is moving north. By the right-hand rule, the magnetic field points upward, toward the sky, for the magnetic force to point toward the west. c. For zero net force on the electron, the magnetic force balances the electric force. Set the magnitudes of the forces equal and solve for the magnetic field. As derived before, the direction of the field is upward. $$qE=qvB$$ $$B=\frac{E}{v}=\frac{330V/m}{3.0\times10^4m/s}=0.011T$$ d. If the electron moves faster than that speed, the magnetic force exceeds the electric force. The electron would accelerate westward. If it is moving slower than that speed, the electric force exceeds the magnetic force. The electron would accelerate eastward. e. As before, the two forces must cancel for the electrons to have no net force. The ratio of the electric field to the magnetic field is v. $$qE=qvB$$ $$v=\frac{E}{B}=5.5\times10^4m/s$$ We cannot find B without knowing E.
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