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Kirchhoff’s voltage law (KVL)

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Presentation on theme: "Kirchhoff’s voltage law (KVL)"— Presentation transcript:

1 Kirchhoff’s voltage law (KVL)
Voltage (potential difference): total work per unit charge associated with the motion of charge between two points. 1 volt (V) = 1 joule (J) / coulomb (C) Potential energy: qV, produced by electric field mgh, produced by gravitation field

2 Kirchhoff’s voltage law (KVL): Cont.
The sum of voltages around a closed loop is zero. -v1 + v2 = 0 + - Potential different (V) vs. potential (V) Potential: at each node, va, vb Potential difference: v2=va-vb Ground: true ground (earth) chassis ground (enclosure)

3 Circuit Elements and Their i-v Characterisitcs
Resistance and Ohm’s Law: Resistance (R) depends on materials and geometry, and resistivity (r) only depends on materials.

4 Electric Power Electric power: moving charge  doing work (energy)
Power (P) = Work / time = work / charge x charge / time = V I P = Joules / sec = Watts (W) What are paying for electricity bill ? kW H = energy

5 More on Resistance Home electric appliances: what does a 1000 W hair dryer tell you? Always assume 120V if the voltage is not specified. Never exceed the rated power. Can you use these appliances in 220 V lines. You destroy the appliance! You can use appliances rated with 220V in 110 V, but with much lower power than rated. (Exercise)

6 Open and Short Circuits
Short Circuit: R=0, v=0 for any i. Particularly bad for voltage source. Open Circuit: R  ∞, i=0 for any v. Particularly bad for current source.

7 Series Resistors and the Voltage Divider Rule
Series Circuit: One branch  same current through each resistor. Voltage Divider:

8 Example: voltage divider
If you want to use your car battery (12 V) to power your laptop computer which requires 3V power supplier, how would you do it.

9 Parallel Resistors and the Current Divider Rule
Parallel Circuit: resistors share the same terminal  same voltage on each resistor. Current Divider: Large current though smaller R Advantage of parallel circuit: a broken branch will not affect other branches

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