# Current and Resistance

This lecture is based on HRW, Sections 28.1 - 28.6. It covers more than we will discuss in class.
• Electromotive force is just another way to say the voltage produced by a battery
• Combining resistors in series produces an overall resistance of
```             Req = R1 + R2 + .... + Rn
```
• Combining resistors in parallel produces an overall resistance of
```              1              1
--- = ------------------------
Req   1/R1 + 1/R2 + ... + 1/Rn
```
• Kirchoff's Rules permit one to solve for the current running through a complex circuit with batteries and resistors
1. The sum of currents entering a junction is equal to the sum of currents leaving that junction
2. The sum of voltages across circuit elements in any closed circuit loop is equal to zero
• Applying Kirchoff's Rules to circuits often results in a set of simultaneous equations, which may be solved for the desired quantities

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