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PHYS 219 Recitation. Kevin Ralphs Week 4. Overview. HW Questions Kirchoff’s Rules Capacitors, Current, Time. Kirchoff’s Rules. Loop Rule Based on conservation of energy Node Rule Based on conservation of charge. Kirchoff’s Rules. General Procedure:
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PHYS 219 Recitation Kevin Ralphs Week 4
Overview • HW Questions • Kirchoff’s Rules • Capacitors, Current, Time
Kirchoff’s Rules • Loop Rule • Based on conservation of energy • Node Rule • Based on conservation of charge
Kirchoff’s Rules General Procedure: • Choose loops so that every branch is covered by at least one loop • Choose current directions in each branch – this does not have to correspond to the direction of your loop • Write down each loop/node equation and solve using method of your choice. You need as many independent equations as you have currents to solve.
Kirchoff’s Rules • The most common errors in applying Kirchoff’s rules are sign errors Voltage Source Resistor (Black arrows denote a positive change in voltage; red negative) Current
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