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 fieldmgh, 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, vbPotential difference: v2=va-vbGround: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 IP = Joules / sec = Watts (W)What are paying for electricity bill ?kW H = energy
5 More on ResistanceHome 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 RAdvantage of parallel circuit: a broken branch will not affect other branches