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# 7. kirchhoff s_rules

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### 7. kirchhoff s_rules

1. 1. Kirchhoff’s Rules<br />
2. 2. Kirchoff’sRules: Junction Rule<br /><ul><li>The algebraic sum of the currents into any junction is zero.
3. 3. A junction is an intersection of three or more conductors.</li></li></ul><li>Kirchoff’sRules: Junction Rule<br /><ul><li>The algebraic sum of the currents into any junction is zero.
4. 4. I = 0 ( at any junction )
5. 5. I is + when it enters a junction.
6. 6. I is - when it enters a junction.
7. 7. I = 0
8. 8. I1 + I2 - I3= 0
9. 9. I1 + I2 = I3</li></ul>I3<br />
10. 10. Kirchoff’sRules: Loop Rule<br /><ul><li>The algebraic sum of the potential differences or voltages in any loop, including those associated with emfs and those of resistive elements, must equal zero.
11. 11. A loop is any closed conducting path.
12. 12. V = 0 ( at any loop)
13. 13. 3 loops</li></li></ul><li>Kirchoff’sRules: Loop Rule<br /><ul><li>Sign convention for V:</li></ul>+V<br />-V:<br /><ul><li>electron flow</li></li></ul><li>Examples:<br />1. The circuit shown contains two batteries, each with a voltage and an internal resistance, and two resistors. Find: (a) the current in the circuit and (b) the potential difference Vab.<br />-<br />+<br />I<br />-<br />+<br />I<br />I<br />I<br />+<br />-<br />I<br />-<br />+<br />
14. 14. Examples:<br />2. In the circuit shown, find: (a) the current in resistor R; (b) the resistance R; (c) the unknown voltage V and (d) if the circuit is broken at point x, what is the current in resistor R? (Ans. (a)2.00 A, (b) 5.00 , (c) 42.0 V, (d) 3.5 A )<br />V=?<br />a<br />b<br />
15. 15. Examples:<br />3. Find the voltages V1 and V2 in the circuit below and find the potential difference of point b relative to a. (Ans. V1=18.0 V, V2=7.00 V, Vba=-13.0V.)<br />V1=?<br />V2=?<br />
16. 16. ---FIN--- <br />