18.25. Set Up: Apply with and Solve: (a) An electron gains energy when it moves to higher potential, so and so (b) Reflect: A positive charge gains kinetic energy when it moves from high potential to low potential but a negative charge gains kinetic energy when it moves from low potential to high potential. 18.26. Set Up: From Problem 18.25, for a particle with charge of magnitude e. The speed of light is An electron has mass and a proton has mass Solve: (a) (b) From Problem 18.25, the kinetic energy the particle gains is so gives electrons and protons the same kinetic energy. But the protons must be accelerated by a potential decrease whereas the electrons are acceler-ated by a potential increase. (c) 18.27. Set Up: and Solve: (a) so which is constant. Let the accelerating voltage. Then and Thus (b) so Reflect: If the charge is positive it is accelerated by a decrease in potential. If it is negative it is accelerated by an increase in potential. 18.28. Set Up:
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