Lab 2: Summary Questions

Today we observed that the fully charged capacitor began to discharge immediately after being disconnected from the voltage source (batteries) prior to it being placed in the circuit with the ohmic resistor.  The reason for this is that the BK DMM has its own internal resistance and therefore an RC circuit existed with the DMM and the capacitor.  So be aware that sometimes measuring instrumentation can influence the value of what is being measured!

It turns out that the internal resistance of the BK DMM when measuring voltage is 10M Ohm.  This value is generally great enough to not influence voltage measurements.  It certainly is fine for what we do in Lab.  However an ideal volt meter should have infinite internal resistance. There are volt meters available with extremely high internal resistance, but as you might guess, these are much more expensive than our BK DMM’s.

Given that the internal resistance of the BK Voltmeter is 10M Ohm, what is \(\tau\) (without uncertainty) of the RC circuit consisting of just the DMM and the capacitor?

Background Equipment Data Collection and Analysis

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