Download DC Circuits Lab: Exploring Ohm's Law, Diodes, and Voltage Dividers and more Lab Reports Physics in PDF only on Docsity! Lab Date Lab 1: DC Circuits Student Name1, name1@ufl.edu Student Name2, name2@ufl.edu I. Introduction The purpose of this lab is to allow the students to become comfortable with the use of lab equipment, through exercises involving simple DC circuits. This lab introduces us to the use of a power supply, multimeter, and voltmeter. We examine the properties of DC circuits containing resistors and diodes. We also become familiar with the use of an oscilliscope and a function generator. In this lab we will be connecting a DC power supply to circuits containing various resistive sources (resistors, light bulbs, diodes). We plot voltage (x-axis) vs current (y- axis) and compare the plots for the various setups. This will allow us to understand the following: how voltage and current are affected by devices that follow Ohm’s law, devices that are not ideal resistors, and devices that do not follow Ohm’s law. We also try to calculate and build a Thevenin equivalent circuit. II. Results 1-1. Ohm’s Law A. Experimental Setup We connect a power supply, voltmeter, multimeter, and resistor to the breadboard. Circuit Diagram: B. Results 12 k Resistor V (V) I (mA) 1.00 0.084 2.00 0.169 2.99 0.252 4.00 0.338 4.99 0.422 10.00 0.846 18 k Resistor V (V) I (mA) 1.00 0.055 2.00 0.112 3.00 0.168 4.00 0.224 5.00 0.280 10.00 0.561 V vs. I 0 20 40 60 80 100 120 140 0 1 2 3 4 5 6 Voltage (V) C u rr e n t (m A ) The curve is not linear. Instead, it curves down slightly towards the voltage axis. Thus, the light bulb does not obey Ohm’s Law. Since resistance can be thought of as the derivative of voltage with respect to current, the light bulb has no clear, constant resistance. Instead, one can only specify the resistance as a function of the current. One possible explanation for the funny shape of the curve is that as voltage increases, the lamp filament heats up. This heating can directly change the resistance of the filament. Another possible explanation is that as the light bulb grows brighter and heats up, more power is extracted from the circuit. This power is tapped from the current, causing the curve to slope down as it does. 1-3. The Diode A. Experimental Setup We connect two resistors in series to a multimeter. The multimeter is also connected to a diode, and to a voltmeter. Circuit Diagram: B. Results 1N914 Diode V (V) I (mA) 0.37 0.009 0.45 0.045 0.48 0.088 0.53 0.210 0.54 0.297 0.56 0.403 V vs. I 0 0.1 0.2 0.3 0.4 0.5 0 0.2 0.4 0.6 0.8 1 Voltage (V) C u rr e n t (m A ) V vs. I Semi-Log Plot 0.001 0.01 0.1 1 0 0.2 0.4 0.6 0.8 1 Voltage (V) C u rr e n t (m A ) The linear plot curve looks exponential. The semi-log plot curve looks linear. Thus, we can safely assume the V-I dependence is exponential. If you were to put 5 volts across the diode, as the curve tells you, the current would increase to a gigantic amount. This would definitely blow out the diode. When we reversed the direction of the diode, no current flowed across it, no matter what resistor value we used. 1-4. Voltage Divider A. Experimental Setup Circuit Diagram: Open circuit output voltage: 7.56 V Loaded circuit output voltage: 5.05 V Short circuit current: 1.497 mA VTh = Vopen = 7.56 V RTh = VTh / Ishort = 7.56V / 1.497mA = 5.05k Thevenin Circuit Diagram: Open circuit output voltage: 7.59 V Loaded circuit output voltage: 5.02 V Short circuit current: 1.474 mA The Thevenin equivalent circuit behaves identically to the original circuit, as expected. Open Loaded
