# Reading current through a capacitor

• limofunder
In summary, when biasing a voltage with Langmuir probes, you must place a resistor between the probes and the ammeter to get a reading of the current density in the plasma.
limofunder
I am working on an experiment involving Langmuir probes. I believe the probes act as capacitors when placed in a plasma to get a reading of the current density in the plasma. However, since we are biasing a voltage, I know that in order to read the current we must insert a resistor between the probes and the ammeter. How should this resistor be placed, in series or in parallel?

You don't need a resistor if you are using an ammeter. The only time is you need a resistor in series is if you want to use a VOLTMETER to read a current (in which case you get the current from I=U/R).
But maybe I missunderstood the question? There could be other reasons for putting a resistor in series (e.g. current limiting) but that has nothing to do with the ammeter.

f95toli said:
You don't need a resistor if you are using an ammeter. The only time is you need a resistor in series is if you want to use a VOLTMETER to read a current (in which case you get the current from I=U/R).
But maybe I missunderstood the question? There could be other reasons for putting a resistor in series (e.g. current limiting) but that has nothing to do with the ammeter.

Yes, I apologize, I understand the ammeter already has internal resistors to measure the current. I plan to run this through a DAQ which requires a resistor to measure the current sent to the computer (the program I'm using asks for a resistance value since the DAQs are configured to measure potential), and I wasn't sure if I should have the resistor in series with or parallel to the probes.

Totally out of my field but I think at least with the double probe it is biased between the 2 electrodes and current across or through the sensor is measured. The bias voltage is varied to extract specific current v.s. voltage anomalies. Can be thought of as a source/measure device. The plasma is the current sense "resistor" albeit very non-linear but that's what your looking for right ?

## 1. What is a capacitor and how does it work?

A capacitor is an electronic component that stores electrical energy in the form of an electric field. It is composed of two conductive plates separated by an insulating material called a dielectric. When a voltage is applied to the capacitor, one plate becomes positively charged and the other becomes negatively charged, creating an electric field between them. This electric field stores energy, which can then be released when the capacitor is connected to a circuit.

## 2. Why is reading current through a capacitor important?

Reading current through a capacitor is important because it allows us to understand how the capacitor is behaving in a circuit. Capacitors can affect the flow of current and voltage in a circuit, and by reading the current through it, we can determine its role in the overall circuit operation.

## 3. How do you read current through a capacitor?

To read current through a capacitor, it must be connected in series with a current measuring device, such as an ammeter. The capacitor will then act as a barrier to the flow of current, and the ammeter will measure the amount of current that passes through it. The reading can then be recorded and analyzed to understand the behavior of the capacitor in the circuit.

## 4. What factors affect the current flow through a capacitor?

The current flow through a capacitor can be affected by several factors, including the capacitance of the capacitor, the voltage applied to it, the frequency of the current, and the type of dielectric material used. These factors can influence the amount of charge that can be stored in the capacitor and how it affects the current flow in the circuit.

## 5. Can current flow through a capacitor continuously?

No, current cannot flow through a capacitor continuously. Capacitors are designed to store electrical energy, not to conduct continuous current. Once the capacitor is fully charged, it will act as an open circuit, preventing any further current flow. However, in AC circuits, the current can flow through the capacitor as it charges and discharges with the changing voltage.

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