Experimenting with RC and RL series circuits using smartphones as signal generators and oscilloscopes

Abstract

Simple, portable and low-cost experiments as RC and RL series circuits are proposed to experiment with DC circuits. Very common elements are used: a few electronics components (resistors, capacitors, coils and connecting wires) and two smartphones. We consider the charging and discharging of a capacitor in the RC circuit and also that of coil in the RL circuit. Using a smartphone as an oscilloscope we observe voltages variations which are the transient response to a square signal generated in the second smartphone. These voltage variations are directly related to the electrostatic or magnetic energy stored in the circuits. The experimental data have been collected with the smartphone used as an oscilloscope and corroborated with theoretical predictions based on Kirchhoff's laws. The comparison showed differences of the order of the 1% or less between the calculated capacitance or inductance compared to the manufacturer values. This approach which avoids the use of expensive signal generators, oscilloscopes, or any specialized hardware can be performed in less-favored contexts and even as a home assignment.

The internal resistance of a non-ideal inductor in an RLC series circuit at resonance

“…The sinusoidal electric signal sent to the audio port is bypassed by means of an audio-jack connector and used to power the RLC circuit. The reader can find more information about this setup in [5,10].…”

“…We have not used a second smartphone as an oscilloscope as in previous works [5,10] because it does not seem to be possible, to the best of our knowledge, to use a smartphone to visualize two signals at the same time. This is why we have used a conventional oscilloscope instead which also allows to measure small phase shifts accurately.…”

“…introductory physics courses [1][2][3][4][5][6][7][8][9] Examples of published works include the study of charge and discharge of a capacitor in an RC series circuit [1][2][3] and current variations upon connecting and disconnecting an RL series circuit [4,5]. In relation to RLC series circuits [6][7][8][9] an important phenomenon to look at is resonance.…”

“…The study of these simple circuits has been addressed in very recent works by using smartphones as signal generators and as oscilloscopes where the signals are sent in and out through the audio port by means of a jack connector [5,10]. The smartphone can be turned into a signal generator by using the Tone Generator option available in the free app for Android Physics Sensors Toolbox Suite [11].…”

“…Similarly, the smartphone can be turned into an oscilloscope by using an audio jack has been used the option Audio Scope included in the free Android app phyphox [12]. By using these possibilities of the smartphones, RC [5], RL [5], and RLC [10] series circuits have been made simple and portable.…”