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Practice question ( join code: 540522 for 2 pm ; 584961 for 3 pm )

Practice question ( join code: 540522 for 2 pm ; 584961 for 3 pm ) Who was mostly responsible for arbitrarily choosing the negative sign (–) that we now use to designate the sign of the electric charge carried by the electron? A. Andre-Marie Ampere B. Charles Augustin de Coulomb

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Practice question ( join code: 540522 for 2 pm ; 584961 for 3 pm )

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  1. Practice question (join code: 540522 for 2 pm; 584961 for 3 pm) Who was mostly responsible for arbitrarily choosing the negative sign (–) that we now use to designate the sign of the electric charge carried by the electron? A. Andre-Marie Ampere B. Charles Augustin de Coulomb C. Benjamin Franklin D. Georg Simon Ohm E. Alessandro Volta Oregon State University PH 213, Class #2

  2. Review: The Law of Gravitation expresses the magnitude of the gravitational attraction force between two masses: |FG| = Gm1m2/r122 where r12 is the distance between the two centers of mass, and G is the universal gravitational constant (G = 6.67 x 10-11 N·m2/kg2). Example: Suppose that a proton (mp = 1.67 x 10-27 kg) and an electron (me = 9.11 x 10-31 kg) are separated by 0.100 nm. Find the magnitude of the gravitational force between the particles. Oregon State University PH 213, Class #2

  3. Coulomb’s Law Coulomb’s Law expresses the magnitude of the electrostatic force between two charges: |FE.21| = |FE.12| = k|q1||q2|/r122 where r12 is the distance between the two charges and k is a constant (k = 8.99 x 109 N·m2/C2). Note the magnitude of the constant, k, suggesting already how much more powerful electrostatic force is than gravitational force. Example: Find the magnitude of the electrostatic (“Coulomb”) force between a proton and electron at .100 nm. Conclusion: When two small bodies with both mass and net charge encounter one another, the force that governs—overwhelmingly—is the electrostatic force. Oregon State University PH 213, Class #2

  4. Example: Point charge A (qA = +2e) sits at x = 0. Point charge B (qB = +8e) sits at x = 1. Point charge C (qC = –37e) sits on the x-axis somewhere between A and B. Charges A and B are anchored (fixed in space). Charge C is free to move, but it remains at rest. Find the x-position of charge C. A.xC = 0.250 B.xC = 0.333 C.xC = 0.375 D.xC = 0.667 E. None of the above. Oregon State University PH 213, Class #2

  5. Example: A point charge of unknown value (q1) is located at the origin. An electron (q2 = –e) is located at the point (4, 0). An alpha particle (that’s a helium nucleus; q3 = +2e) is located at (0, 2). All coordinates are in meters. How many times stronger is FE.31than FE.12? A. 2 B.8 C. 1/4 D. Not enough information. E. None of the above. Oregon State University PH 213, Class #2

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