Physics
Physics
Problem
An electron travels through a region containing two consecutive sets of parallel plates. It begins at plate 1 and ends at plate 3, passing through plate 2 on the way. Measured electric potentials are: • Plate 1: • Plate 2: • Plate 3: Assume the electron is released from rest at plate 1 and that the only force acting on it is electrostatic. Use the electron mass and charge magnitude . (a) Determine the net electric potential difference experienced by the electron as it travels from plate 1 to plate 3. (b) Calculate the change in electric potential energy of the electron–field system over the entire trip. (c) Find the electron’s speed immediately after it has passed plate 3.Intuitive explanation
The key is using energy conservation with electric potential energy rather than tracking forces plate by plate. Since the electron starts from rest, all its kinetic energy at any point comes from the work done by the electric field—which equals the change in electric potential energy. Remember that an electron has negative charge, so it's repelled by negative potentials and attracted to positive ones; the potential energy is (negative charge times voltage). Calculate the total potential difference the electron "falls through" from start to finish, then convert that directly to kinetic energy.
Intuitive explanation
The key is using energy conservation with electric potential energy rather than tracking forces plate by plate. Since the electron starts from rest, all its kinetic energy at any point comes from the work done by the electric field—which equals the change in electric potential energy. Remember that an electron has negative charge, so it's repelled by negative potentials and attracted to positive ones; the potential energy is (negative charge times voltage). Calculate the total potential difference the electron "falls through" from start to finish, then convert that directly to kinetic energy.