38. one point, from Lecture 39, one diagram and short explanations

(a) .4 Feynman Diagram. Draw the Feynman diagram for two electrons approaching each other and exchanging a virtual photon (.1), and give the rules for external lines (.1), internal lines (.1), and vertices (.1).

(b) .2 Virtual Particle. How does the Uncertainty Principle allow the existence of a virtual particle (.1)? What do a photon and a virtual particle have in common (.1)?

(c) .2 Newton Lives! What are the two key differences (.1 apiece) between the new quantum rule for force in quantum electrodynamics (QED) and Newton's Second Law (in the form of change of momentum over time)?

(d) .2 Electric Charge. State the new role for electric charge in QED (.1) in a way which makes it clear that this is just a quantum version of the classical role for charge (.1).

Revised December 2, 1997.