In: Physics
The very high internal resistance of digital multimeters, in their voltage-measuring ranges, can be used to measure extremely low currents (even though the DMM may not offer a low current range explicitly). Suppose, for example, you want to measure the small current that flows through a 1000 M ohm "leakage" resistance (that term is used to describe a small current that ideally should be absent entirely, for example through the insulation of an underground cable). You have available a standard DMM, whose 2 V dc range has 10 M ohm internal resistance, and you have available a dc source of +10V. How can you use what you've got to measure accurately the leakage resistance
We can measure the leakage current by connectin everything in series. Then we can use the voltage divider equation to find the leakage current.
As you know the electrical components when connected in series have the voltage divided across the components, according to their resistance. Thus we can use this principle to get the I leakage. Please refer to the following image
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