Bergen Community College Physics II Lab Ohm’s Law PHY 290-002 Written By: Sait Bilal Cantas Team Members: Bruce Le, Mikhaiel Myshkin Prof. Haldo Date of Experiment: October 5, 2018 Report submitted on: October 13, 2018 OBJECTIVES: In this lab we observed and considered Ohm’s Law experimentally. The purpose of this lab was to verify Ohm’s Law, which explains current-voltage relationship in examining circuit resistance. PHYSICAL PRINCIPLES: Ohm's law has been one of fundamental principle in the field of electrical circuit. Ohm's suggested that a linear relationship existed between current flowing through the circuit and the voltage change in the circuit. As such a constant has to be present for such a relationship to be feasible. The constant is resistance. In equation form, Ohm’s law is: V = IR Where R is the resistance. Measured in Ohms. I, the current. Measured in amperes. V is the voltage. Measured in volts. As such a resistor, or any object with electrical resistance, the amount if current flowing through it has a direct correlation with the voltage recorded in the object. Assuming that a constant voltage is introduced in the object, then there will be an inverse relationship between the current and the resistance in the object. In the case of negative voltage, a reverse in the flow of current will happen. As such, the hallmark of Ohms law is, R = V/I where R, resistance is a constant, independent of V, voltage and I, current. Current measures the number of electrons in a certain point of electrical circuit in a given duration of time. The change in electrical potential, voltage influences the flow of current in a circuit. As such, the flow of current is such that it will flow from an area with high electrical potential to area with low electrical potential. This is owing to the fact that electrons in a circuit usually from a low electrical potential area, since like charges repel to a region with the opposite charge, that is high electrical potential. Some materials have very low resistance while others have high resistance. Low resistance materials are called conductors. High resistance materials are called insulators. Moderator resistance materials are usually used in making resistors.1,2,3 LIST OF EXPERIMENTAL EQUIPMENT: • Battery (6V) • Connecting wires • Multimeters • Unknown resistance • Decade resistance box • Graph paper • Paper towel PROCEDURE: The experiment was subdivided into parts. We started by checking the apparatus to ensure everything was in present and functional. In the first part of the experiment, we set the resistance of the decade at two values 50 and 30 ohms. The two acted as constants. We first did the experiment using the 50 ohms constant then the next part we used 30 ohms. In both, the voltage was adjusted on the ammeter and the respective values of the current recorded. As such, we got values for both voltage and current at 50 ohms resistance, then the values for the same at 30 ohms resistance. In the second part of the experiment, we created simple circuit with unknown resistance in the circuit. The connecting wires were joined to the battery and ammeter. The voltage was systematically decreased, and the respective current reading was recorded. This was aimed at determining the resistance of the material. In the last part of the experiment we arranged the apparatus as we did in the first part, then set the voltage of the ammeter at a constant level, 2.68v. In this case, the resistance of the circuit was adjusted using the decade resistance, starting from 100 and decreasing by 20. The equivalent values of the current were measured at each step. We thereafter drew the respective graphs in Microsoft excel. CALCULATIONS: The following equation was useful in our calculations: The calculations are provided. DATA TABLE 1 Terminal voltage: 30 CONSTANT 50ohm CONSTANT 30ohm Reading Voltage Current Voltage Current 1 4.89 0.09 4.72 0.15 2 3.52 0.07 2.95 0.09 3 2.77 0.05 2.15 0.07 4 2.28 0.04 1.69 0.05 5 1.95 0.03 1.39 0.04 Slope of lines: Percent error: 48.164 3.672% 30.539 1.796% In this part, 50 ohms and 30 ohms of electrical resistance were used. A constant level of voltage was thereafter used and the respective values of current measured. The graph plotted was thus of voltage against current. This represented the resistance used. The slope of the first graph generated was 48.164. The actual resistance for this was 50 ohms. As such an error of (5048.164)/50*100= 3.672% had occured in the experiment. In the second part, the gradient of the graph was 30.539. The actual resistance in the experiment was 30 ohms. Thus an error of (30.539-30)/30*100 = 1.796% had occured. Chart Title 6 y = 48.164x + 0.3848 4 2 0 0 0.02 0.04 0.06 0.08 0.1 Chart Title 5 y = 30.539x + 0.1368 4 3 2 1 0 0 0.02 0.04 0.06 0.08 DATA TABLE 2 READING VOLTAGE CURRENT 1 9.94 0.11 2 8.23 0.09 3 7.03 0.07 4 6.13 0.06 5 4.90 0.05 6 4.44 0.04 7 3.48 0.03 Slope: 80.225 0.1 0.12 0.14 0.16 In this experiment, the aim was to calculate the resistance of the material used. A certain amount of voltage was used, as shown the table, and the corresponding current measured. The voltage would thereafter be reduced and the respective current measured too. A graph generated from this would thus be voltage against current. This corresponds to resistance. As such, we found out that the value of the unknown resistance material was 80.225 ohms. Chart Title 12 10 y = 80.225x + 1.1499 8 6 4 2 0 0 0.02 0.04 0.06 0.08 0.1 0.12 DATA TABLE 3 CONSTANT VOLTAGE: 2.68V READING CURRENT RESISTANCE I/RS 1 0.02 100 (50) 0.01 2 0.03 80 (33) 0.0125 3 0.04 60 (27) 0.0166 4 0.06 40 (20) 0.025 5 0.12 20 (8) 0.05 Slope of lines: 2.4478 Percent error from Vs: 8.6642% The results above show the results obtained from an experiment with a constant voltage of 2.68 V. The various values of current and resistance were recorded. We later calculated the values of current/resistance. A graph was thereafter generated of current against current/resistance. The graph is shown below. The gradient obtained from the graph would therefore represent the voltage used in the experiment. The gradient was 2.4478. Our actual voltage used in the experiment was 2.68 V. As such, it is clear that there was an error of (2.68-2.4478)/2.68 *100% This correlates to 8.6642% error. Chart Title 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 y = 2.4478x - 0.0019 0 0.01 0.02 0.03 0.04 0.05 0.06 DISCUSSIONS: Resistance is a constant of current and voltage. In our experiment, this was clearly brought out as linear graphs were generated from such. A graph that plotted current vs voltage led to a linear relationship. A constant of which comprises of the resistance. Certain factors affected the effectiveness of our outcome thus making the results to have some errors. For instance, in one experiment we used a resistance of 30 ohms, yet the value we found from our experiment was 30.539 thus the error witnessed can be calculated as (30.539-30)/30*100 = 1.796% Such factors include; The resistance of the unknown object might not have been perfect, some parts might have had higher or lower electrical resistance than others, The apparatus used might have had slight errors that affected the outcome. Human errors, our measurement and recordings might have not been perfect. CONCLUSION: In our experiment, it turned out clearly that a relationship existed between the current, voltage and resistance recorded. The circuit behavior was as such in line with the Ohms law. Resistance of unknown object could be measured using the respective current, and voltage. For instance, in one of the experiments, the values obtained from voltage and current were used to plot a graph of voltage against current. The value of the gradient was thus the resistance as Ohms law states that R=V/I. Thus the 80.225 ohms was the value of the unknown object. As such, this clearly indicated that there was a direct relationship between the two. The voltage, could as well be manipulated in order to enable collection of other data such as resistance, which goes in line with the concept presented by Ohms law. The different configurations of the circuit, parallel or series, played a role in giving different results as such, their significance in Ohms law cannot be ignored. Thus, the experiment rightly validated Ohms law. QUESTIONS: 1) If the switch were kept close during the procedures and the circuit components heated up, how could this affect the measurements? A switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another. The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts. Each set of contacts can be in one of two states: either 'closed' meaning the contacts a retouching and electricity can flow between them, or 'open', meaning the contacts are separated and nonconducting. When the switch is closed the current flows through the circuit. Then the circuit components heated up. Measurement system requirements such as accuracy, speed, and number of DUTs, dictate the equipment and cabling that can be used within the ATS. As requirements become more stringent, general use-case measurement techniques and switching configurations may no longer deliver adequate performance when the circuit is heated up. So, we can’t get accurate measurements. 2) Devise and draw a circuit using a long, straight wire resistor, instead of a decade box, that would allow the study of the variation of voltage with resistance. According to Ohm’s Law, what would a graph of the data from this circuit show? The figure is as shown below. Now the potential across the resistor is proportional to the current across the resistor or V α I or V = RI Where R is a proportionality constant or R = V/I When you summarize the results graphically, we get 3) Compute the values of Rh and the voltage drops across this resistance for the two situations in TI data table 1, reading 1. How the values compare? Terminal voltage: Vt = 30.00V RS =50.00 ohm VS= 4.89V IS= 0.09A Series current is same in all parts of circuit. IS= Vt / (Rs + Rh) 0.09 = 30.00 / ( 50.00+Rh) Rh = 283.3ohm Rs= 30.00 ohm Vs= 4.72V Is= 0.15A Vt= 30.00V IS= Vt / (Rs + Rh) 0.15A = 30.00 /(30.00+Rh) Rh= 170.0ohm REFERENCES: 1 Halliday, David, et al. Fundamentals of Physics. 10th ed., Wiley, 2014. 2 Schroeder, Peter A. “Electrical Resistance.” AccessScience, McGraw-Hill Education, 2014. 3 Wilson, Jerry D, and Hall Cecilia A. Hernandez. Physics Laboratory Experiments. Custom ed., Cengage Learning, 2015. DATA:
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