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Part E review

Part E review. March 9, 2012. Three “rules”. Charge is conserved (#1) Current flowing into a location = current flowing out V=IR (#2) Voltage across object is related to current through it (definition of resistance)

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Part E review

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  1. PHYS132 Spring 2012 Part E review March 9, 2012

  2. PHYS132 Spring 2012 Three “rules” Charge is conserved (#1)Current flowing into a location = current flowing out V=IR (#2)Voltage across object is related to current through it(definition of resistance) Energy is conserved (#3)For every complete path,total voltage provided by batteries = total voltage dissipated by other elements

  3. PHYS132 Spring 2012 Using rule #1 (Charge is conserved) • What you should be able to do: Determine current given other currents • Series circuit: Current in a series circuit is the same throughout the circuit • Parallel circuit (see below): How are Itotal, I1, I2 and I3 related?

  4. PHYS132 Spring 2012 Using rule #3 (Energy is conserved) • What you should be able to do: Determine voltage given other voltages • Series circuit: Voltage is split among the elements • Parallel circuit (see below): Voltage across each branch is the same

  5. PHYS132 Spring 2012 Using rule #2 (Definition of resistance: Ohm’s law: V=IR) • What you should be able to do: Given two of V, I and R, find the third • This can be applied to individual elements or to total circuit

  6. PHYS132 Spring 2012 Using rule #2 (continued) • Series circuit: voltage across each element is less than total voltage (rule #3) • so current through each element is less than if it were present alone (V=IR) • same total voltage but less total current (rule #1) • so total resistance is more (V=IR)

  7. PHYS132 Spring 2012 Using rule #2 (continued) • Parallel circuit: voltage across each element is same as total voltage (rule #3) • so current through each element is same as if it were present alone (V=IR) • same total voltage but more total current (rule #1) • so total resistance is less (V=IR)

  8. PHYS132 Spring 2012 Equivalent resistance Resistors in series  Resistance is higher than highest resistance Resistors in parallel  Resistance is lower than lowest resistance

  9. PHYS132 Spring 2012 Examples • Three resistors are in series: 1 Ω, 2 Ω and 3 Ω. What is total resistance? • What if they were placed in parallel?

  10. PHYS132 Spring 2012 Mixed circuit • Order the currents (Itotal, I1, I2, I3) from largest to smallest. • Which branch has the largest equivalent resistance? • How are the voltages related?

  11. PHYS132 Spring 2012 For Monday after break • Exam on parts A through E • Nothing due for Wednesday after break • Second half of textbook should be available that week

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