TOPS Physics
Teacher Reference
Introduction:
In this exercise, students verify experimentally Kirchoff’s Loop and Junction Rules for
DC circuits.
Experimental goals:
After completing this experiment, students will be able to determine the value of
resistors from their color codes, assemble components as instructed on a
breadboard, and state and define Kirchoff’s Loop and Junction. They will also be
able to take resistance, voltage, and current measurements with a digital multimeter.
Equipment:
Electronics Trainer
Multimeter
Resistors: 1000, 2200, & 4700Ω
Keywords:
Resistance, Voltage, Current, Kirchoff’s Loop and Junction rules, Parallel Circuits,
Series Circuits.
Notes:
The biggest danger in this lab is that students will leave the red meter probe
connected to the current (“µAmA”) terminal of the meter. If they then put the probes
across a voltage source they will blow the fuse inside the meter. For this reason,
current measurements are left to last, and the students are instructed specifically on
what to do. Make sure that the red probe is kept plugged into the “VΩ” terminal
unless the students are actively taking current measurements! If you get a meter
that reads “0” when trying to make a current measurement, you can pretty much be
sure that the fuse is blown!
If the voltage and current reading are fluctuating, try wiggling the components and
jumpers to make better contact with the breadboard
Answers:
The experiment verified Kirchoff’s loop rule because the voltages around a loop did
add up to zero.
The experiment verified Kirchoff’s junction rule because the currents going into a
junction equaled those going out of a junction.
Possible sources of error:
1. Resistors not of the marked value
2. Meter might not be accurate
3. Mathematics errors
4. Precision (number of significant digits) error
5. Stray resistance in circuit due to jumpers, connections, etc.
6. Changes in supply voltage while circuit is being measured.
TOPS Electronic Trainer Kirchoff's Laws.doc
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