# appropriate resistance value

Measuring the capacitance of a reed switch

A variable resistor is connected in series with the microammeter to protect it from damage.

To set an appropriate resistance, connect the Y-input of a CRO across the variable resistance to monitor the pulse of discharge current through it. Set the variable resistance to the highest resistance so theat the capacitor discharges incompletely.Gradually reduce the resistance until the capacitor can just completely discharge.

Apart from the above method, suggest another method for setting an appropriate resistance value?

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Measuring the capacitance of a "reed switch" looks odd. I think you refer to the capacitance of a given capacitor, not the reed switch.

I don't known how your circuit is connected. Since you have mentioned that the variable resistance is connected in series with a microammeter, I further presume that the microammeter is connected in series with the capacitor so as to measure the discharge current.

The simplest way is to adjust (decrease) the variable resistance until the reading on the microammeter shows no further increase, i.e. a steady current is obtained. This is the appropriate resistance value for complete discharge of the capacitance. It is because on complete discharge, no more charges (and hence current) could be obtained from the capacitor by further decreasing the variable resistance.

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