Day 13 Capacitor Voltage-Current Relations

The purpose of today's lab is to measure the relationship between capacitor voltage and capacitor current. The voltage applied will be three different types of time-varying signals: sine wave, triangle wave, and square wave voltages will be applied. Because our analog discoveries do not measure current we will use a math function to calculate the current.

From our studies we know that


Ic = C dv/dt

Below is a sketch of our pre-lab activity. Given a sinusoid and triangle wave input voltage, draw the resulting current. Current in a capacitor is proportional to the derivative of the voltage and our sketches reflect that below.

Lab :

The components we used in this lab were simply a 1uF capacitor and a 100 Ohm resistor connected in series. Using the oscilloscope function of the Analog Discovery we measure the output voltage of the resistor and the capacitor. By adding a Math Channel of (VR/100(ohms)) we can also see the plot of the current. It mirrors what we predicted.

Applying a 1kHz sine wave to the circuit results in a capacitor current that is proportional to its derivative. Vout for the capacitor is the plot of C2 above, and the current is the plot of M1. As expected, we see a plot of a sine and cosine wave.

Below is a 2kHz plot of the same:

Below is our successful circuit.

We were able to successfully measure, observe, and apply current- voltage relationship through a capacitor.