In the fiesta of knowledge we were asked to find the resistance and resistivity of a copper extension cord, the max current through a copper wire and some other stuff that I do not remember.
After the fiesta we started unit 7: Direct current circuits,we skipped the first couple sections.
we started on 7.7 Using a multimeter
we built a circuit with a resistor and were given a multimeter.
We learned how to use the multimeter to measure measure DC current(amps), potential difference (volts) and resistance and this is how is done for the multimeter we were using:
1)To measure DC current the selector on the multimeter has to be on Amps, the correct range, connected in series with the circuit element and the positive test lead in the amps receptacle.
2)To measure potential difference(volts) the selector has to be in volts, correct range, connected parallel to the circuit element, and the positive test lead in the volts receptacle.
3)To measure resistance(ohms) the selector has to be on ohms, correct range, the resistor has to be disconnected from the battery, and the positive test lead in the resistance receptacle.
the negative test lead stays at the same position on the negative charge receptacle for this multimeter.
Then we moved on to Electric Power
we found out that if you multiply voltage (Joules/coulombs) and current (coulombs/seconds) the coulombs cancel and we end up with Joules/seconds which are the units for power. so, we get the definition of power:
P=VI (power=voltage X current
Resistance and its measurement
In a circuit potential energy is lost due to resistance. one of the most common resistors is the light bulb which turns potential energy into heat and light. But most electric circuits use resistors made of carbon, known as graphite, for resistance. Carbon is used because its resistance does not vary with the current passing trough them. They are cheap make and and can be made with low or high resistances.
Carbon resistors are color coded with different color bands that tell us its value in ohms. To get the value of the resistor we use the following table:
The Resistor code Table
Black =0
Brown =1
Red =2
Orange=3
Yellow =4
Green =5
Blue =6
Violet =7
Gray =8
White =9
silver =(+/-) 10%
gold =(+/-) 5%
so this is how we use the table to get the value of a resistor
value of the resistor (ohms)= AB x 10^C (+/-)D
Gold, and silver bands represent the tolerance of the resistors(if your first line is gold or silver turn the resistor around you are reading it backwards).
once you is turned around the fist two color band are A and B.(do not multiply A and B)
A and B are just placed next to each other and that is the first number.
the third color line is the exponent C, and finally the fourth line is you tolerance, D.
Prof. Mason gave a 2 resistors and we calculated their resistance using the Resistance Value Table, the we did the same for some combinations he wrote on the board. Then he proceeded to show what happens when a resistor is subjected to a higher current that what is rated for. Using a generator he burned a poor defenseless resistor to a crisp.
Measuring Resistances in Series and Parallel
We were given two identical resistor and then three identical resistor using a multimeter we measured the resistance in parallel and in series and we found that resistors in series in parallel the voltage stays the same but the two currents add up to the total current.
When we put the resistors in parallel the current stays the same voltages coming from the two resistor in parallel add to the total voltage of circuit
so this are the formulas:
Resistors in Parallel:
1/Req=(1/R1)+(1/R2)+(1/R3)+..........
Resistors in Series:
Req=R1+R2+R3+............
We also found that we have circuit with two resistors in parallel we can find the equivalent resistor using these formulas and then replace it with a single resistor.
Introduction to Kirchhoff 's Laws
First law: Junction Rule(based on charge conservation)
The sum of all the current entering any node or branch point of a circuit entering any node or branch point of a circuit must equal the sum of all currents leaving the node.
Second law: The Loop Law (based on energy conservation)
Around any closed loop in circuit, the sum of all emfs, voltage gains provided by batteries or other power sources, and all potential drops across resistor and other circuit elements must equal zero.
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we stopped because the class ended I agree with professor Mason this class is to short. Thursday, Friday, Saturday, and Sunday, four days without going to class is too much.
P.S I missed some of the stuff we did right after brake because Dante and Joy were holding up the line at the Mountie grill. It took them 25 minutes to order water and a cookie.
BAM!! + BAM! = 2BAM!
Jesus
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