The Laws of Circuit - you can learn and practice by just reading

Copyright. Charles Kim 2006

Do We Need This?
The same old and same old problem pops up once in a while and this semester is not an exception. The culprit is how to measure current through a resistor using a digital Multimeter (DMM). DMM could sound like double coated M&M chocolate candy, but its taste is not that sweet even in the Valentines' Day. DMM can work as a voltmeter, ammeter, and ohmmeter. Measuring the voltage across a resistor seems to be easy to everybody. However, seemingly easy and honest current measurement using a DMM seems to be still uneasy an tasks in lab. Voltage is defined as "voltage across" and measured across a resistor. No problem. Current is defined as "current through" and should be measured through a resistor. Therefore, we have to cut a branch at the end of the resistor, then we connect the two probes of the DMM to the two ends of the cutting. Of course in the DMM, two proper terminals must be selected for the probes. The point in current measurement is that current should flow through the resistor and through the DMM (as Ammeter). In other words, the resistor and the DMM (as Ammeter) should be in series in a branch.