DC Circuits. October 15, 2008. This is the week that will have been. Today Complete Resistance/Current with some problems Friday Examination #2: Potential Resistance & Current Next Week: DC Circuits Next Topic: Magnetism Next Quiz: One week from Friday. Good Luck on the Exam.
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October 15, 2008
Good Luck on the Exam
12 volts 0 volts
The figure below gives the electrical potential V(x) along a copper wire carrying a uniform current, from a point at higher potential (x=0m) to a point at a lower potential (x=3m). The wire has a radius of 2.45 mm. What is the current in the wire?
What does the graph tell us??
*The length of the wire is 3 meters.
*The potential difference across the
wire is 12 m volts.
*The wire is uniform.
Let’s get rid of the mm radius and
convert it to area in square meters:
A=pr2 = 3.14159 x 2.452 x 10-6 m2
A=1.9 x 10-5 m 2
Material is Copper so resistivity is (from table) = 1.69 x 10-8 ohm meters
In this Figure, find the equivalent resistance between points (a) F and H and [2.5](b) F and G. [3.13]
The ideal battery does work on charges moving them (inside) from a lower potential to one that is V higher.
This trip around the circuit is the same as a path through space.
THE CHANGE IN POTENTIAL FROM “a” AROUND THE CIRCUIT AND BACK TO “a” is ZERO!!
ADD ENOUGH RESISTORS, MAKING THEM SMALLER
AND YOU MODEL A CONTINUOUS VOLTAGE DROP.
Watch the DIRECTION !!
Let’s write the equations.
batteries have an emf of 4.0 V. What is the current through resistor R?
Resistors and Capacitors in the same circuit??
Is this cruel or what??
How Fast ?
I need to use E for E
Note RC = (Volts/Amp)(Coul/Volt)
= Coul/(Coul/sec) = (1/sec)
qinitial=CE BIG SURPRISE! (Q=CV)
Looking at the graph, we see that the
resistor dissipates 0.5 mJ in one second.
Therefore, the POWER =i2R=0.5 mW