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PHYS 241 Recitation. Kevin Ralphs 3 Oct 2012. Overview. HW Questions Capacitors, Current, Time Right-Hand Rule and the Cross Product Magnetic Fields Magnetic Moment. HW Questions. Ask Away…. Capacitors, Current, Time.
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PHYS 241 Recitation Kevin Ralphs 3 Oct 2012
Overview • HW Questions • Capacitors, Current, Time • Right-Hand Rule and the Cross Product • Magnetic Fields • Magnetic Moment
HW Questions Ask Away…
Capacitors, Current, Time • You will be responsible for understanding how a capacitor behaves at various times during charging/discharging • The end points are simple • If uncharged, a capacitor acts as a short • If charged, a capacitor acts as an open • The words “after a long time” or similar mean it has gone from charged to uncharged or vice versa
Capacitors, Current, Time • In between it is governed by equations • Note: vary depending on whether you are charging/discharging and what resistors you are charging/discharging through
Right-Hand Rule and the Cross Product • Cross product is perpendicularto BOTH of the vectors in theproduct • You sweep your hand from thefirst vector to the second throughthe smallest angle between • Measures how perpendiculartwo vectors are
Magnetic Fields • Lorentz Force • What does it tell me? • The force a charged particle experiences in an electromagnetic field • For a wire this becomes
Magnetic Fields • Lorentz Force (cont.) • Why should I care? • Forces describe the acceleration a body undergoes • The actual path the body takes in time can be found from the acceleration in two ways • Use integration to get the particle’s velocity as a function of time, then integrate again to gets its position • Kinematic equations (the result when method 1. is applied in the case of constant acceleration) • This along with Maxwell’s equations describe all electromagnetic phenomena
Magnetic Moment • What does it tell me? • How a current loop or magnet responds to an external magnetic field • Why should I care? • This drastically simplifies your calculations • You end up treating it like an electric dipole