RC Circuits - General Physics with Calculus II - Lab | PH 106, Lab Reports of Physics

Download RC Circuits - General Physics with Calculus II - Lab | PH 106 and more Lab Reports Physics in PDF only on Docsity! Introduction At this point you should have connected the lab box to a USB port and started the software. Needed: 4 “banana” wires 1 capacitor 1 resistor 1 BamaLab source/measure box In this experiment we will measure the charging and discharging of a capacitor in an RC circuit. This will allow us to determine the time constant of an RC circuit. Through an independent measurement of the value of the resistor, this will also allow us to determine the value of the ca- pacitor. Figure 1 below shows the basic circuit we will consider. Figure 1: A basic “RC” circuit In the actual lab, the switch S is controlled by the software, as is the value of the source voltage ∆V.If the capacitor C is discharged at time t=0, and we suddenly close switch S, the capacitor will start to charge up. While this happens, the potential difference on the capacitor will follow: The quantity RC is the “time constant” of the circuit, and represents how long it takes to charge the capacitor. If we wait long enough to fully charge the capacitor, and then suddenly close S, the capacitor will discharge through the resistor R. While this happens, the potential difference on the capaci- tor will follow: In our experiment, we will use the lab software to charge and discharge the capacitor while si- multaneously measuring the voltage, giving us our ∆VC(t) curve directly. PH106 Lab: RC Circuits 1/4 !VC(t) = Q C ! 1 ! e!t/RC " = !V ! 1 ! e!t/RC " R !V C S !VC(t) = !V e !t/RC Part I: Charging & discharging the capacitor This laboratory uses the tutorial software and hardware you were introduced to previously. a) Connect your resistor and capacitor in series by stacking the “banana” plugs. b) Connect the free end of the resistor to the “+Vout” terminal on your laboratory box, and the free end of the capacitor to “-Vout” to complete the circuit as shown above. This is for applying a voltage to the R and C in series. c) Connect wires from “+Vin” and “-Vin” to either end of the capacitor. Keep the polarity pre- served, i.e., connect the “-Vin” to the same point that “-Vout” is connected. This is for measuring the voltage on the capacitor.. d) In the tutorial software, choose “Voltage vs. Time” from the “ac Circuits” menu. Figure 2: The voltage vs. time panel. e) We first want to apply a potential difference ∆V for a set amount of time, and then remove it. On the right side of the window, set the “Wait time” to 10 seconds, and choose “Initially” from the “Apply Voltage” pull-down menu. (You can change the voltage if you like, but 2 Volts works well.) These settings mean the program will immediately apply a voltage of 2.00 Volts (or what- ever you choose) once you press “Start V(t)”, leave it on for 10 seconds, and then turn it off. Time “t=0” is defined as the point when the voltage is turned off. f) Adjust the delay time until you see a curve like the one above, such that the curve rises and is nearly flat before t=0. g) Have an instructor verify that your graph is OK and INITIAL HERE _____________ (there is no need to print any plots) PH106 Lab: RC Circuits 2/4