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PHYS 221 Recitation

PHYS 221 Recitation. Kevin Ralphs Week 1. Introduction. TA: Kevin Ralphs Email: kralphs@purdue.edu Web Site: http://web.ics.purdue.edu/~kralphs Office: PHYS 137 Office Hours: Email to request Help Center Hours: M 9:00-11:00, 2:00-3:30 Th 1:30-3:30. Preliminaries.

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PHYS 221 Recitation

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  1. PHYS 221 Recitation Kevin Ralphs Week 1

  2. Introduction • TA: Kevin Ralphs • Email: kralphs@purdue.edu • Web Site: http://web.ics.purdue.edu/~kralphs • Office: PHYS 137 • Office Hours: Email to request • Help Center Hours: M 9:00-11:00, 2:00-3:30Th 1:30-3:30

  3. Preliminaries • Recitations will largely focus on a conceptual approach to the material • Memorization of equations and constants will not help you on the exam • Understanding the concepts sometimes allows you to almost instantly answer a question

  4. Useful Math • Working with Vectors • Solving Systems of Equations • Varying Quantities in an Equation

  5. Coulomb’s Law • What does it tell me? • It tells you the force between two charged particles • Why do I care? • Forces describe the acceleration a body undergoes • The actual path the body takes in time can be found from the acceleration using kinematic equations

  6. Coulomb’s Law • Forces have magnitude and direction so Coulomb’s law tells you both of these • Magnitude: • Direction: Along the line connecting the two bodies. It is repulsive in the case of like charges, attractive for opposite charges

  7. Principle of Superposition • What does it tell me? • The electric force between two bodies only depends on the information about those two bodies • Why do I care? • Essentially, all other charges can be ignored, the result obtained in pieces and then summed… this is much simpler

  8. Electric Field • What does it tell me? • The force a positive test charge would experience at a point in space • Why do I care? • Calculating the force a particular charge feels doesn’t directly tell you how other charges would behave • The electric field gives you a solution that applies to any charge, so it reduces your work • Philosophically,

  9. Electric Field • Electric field due to a point charge at distance r with charge q • Principle of superposition still applies • You can sum individual fields due to discrete charges

  10. Electric Field • Word of caution when summing: • ALWAYS verify what changes from charge to charge • Constants may be removed from the sum • Remember that you are adding vectors, so the direction unit vector often changes between particles

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