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Published byEthan Lawson Modified over 2 years ago

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Potential energy is lost as charge moves through a circuit. This Is measured in Volts. As an electron moves toward the (+) Terminal it will lose potential energy which is usually Converted into heat. The symbol (V) actually means V. V=ED or EL means Energy lost/charge = Force/charge x Length V = ED or EL Work = Force x Distance V = E D D Volts Potential Energy

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Nichrome VoltageAmperes V= E L e e e e V I = 8.4 watts

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Copper Voltage Current V=EL V I =33.6 watts

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Copper Nichrome Voltage Current - electrons

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Go back and check it out!

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Nichrome Copper VoltageCurrent Ed=V V I < V I I I I

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E Length Copper Nichrome Electrons build up at the Cu/Nichrome junction and reduce the electric field in copper while increasing the electric field in nichrome UNTIL the two currents are the SAME. It takes less force (electric field) to push the current through the copper wire than through the nichrome wire. EL= Volts VI=(volts)(3a)= cool V I=( volts )(3a)= HOT

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Cu wire Nichrome wire Electric field in the Nichrome wire must be larger because of its larger resistance. El cu + El nic.= V 6v 6v 2a Cool hot Have students touch the wires. Electric field in a Series Circuit:

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Conclusion about Series Circuits: 1. All the currents must be the same! 2. The resistor with the most resistance must have the largest electric field in it. 3. Therefore, The resistor with the most volts lost (greatest resistance) must get the hottest. V I = watts V = E d

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Copper Nichrome Voltage Current 12 amps 3 amps close to 15

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E Length V=EL Copper Wire Length E V=EL Nichrome Wire 2.8 volts Power= VI Which wire gets Hotter? Power = (2.8 v)(12a)=34watts The resistance of copper wire is small so the current should be larger than in the Nichrome. V I= hotter The resistance of nichrome wire is large so the current should be smaller than Cu. V I= cooler Power=(2.8v)(3a)=8.4watts

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In a parallel circuit the voltages across the resistances are equal. (Logic tells us this must be true) The currents add up to the total current. The electric fields which push the electrons around are equal in each resistor…since V=Ed and the ds are =.

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Copper Nichrome Copper Voltage Current

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E copper nichrome copper Volts lost Volts lost Volts lost L cu = L nichrome Electric force field in the copper wires is very small; as in the previous example the field in the nichrome must be larger to produce the same current throughout. R Extension CordLight bulb Therefore, negligible heat is generated in the ext. cord V I + V I + V I = total power

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In Ohmic devices…..that follow ohms law the current is proportional to the voltage. V α I therefore the ratio of V to I is a constant V/I = constant This constant is called the resistance. Therefore V/I = R or V = IR

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Graphing Ohms Law: A demo on the black- board. VIV Variable resistor: Vary R and record V and I. Graph. V I R =4 R=2 physics.ph. msstate.ed u/jc/library /18- 2/ohmslaw. htm

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In Ohmic devices…..that follow ohms law the current is proportional to the voltage. V α I therefore the ratio of V to I is a constant V/I = constant This constant is called the resistance. Therefore V/I = R or V = IR What happens to the total resistance of a circuit when you add resistors in series??

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Variable resistor: Vary R and record V and I. Graph. V I R =4 R= a b What happens when you add another resistance in series? Is the resistance going up staying the same or going down ?? If you compare slides 4,5,and 7 you can see that adding wires in series increases the resistance and lowers the current. Adding two 2 ohm resistors in series will make the current half and therefore must double the total resistance. Look at the graph from point a to point b. Resistors placed in series have their values added to find the total resistance.

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Conclusion about Series Circuits: 1. All the currents must be the same! 2. The resistor with the most resistance must have the largest electric field in it. 3. Therefore, The resistor with the most volts lost (greatest resistance) must get the hottest. V I = watts V = E d 4. R total = R 1 + R 2 + R 3 etc

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