Unformatted text preview: Introduction to Electrical Measurements Ali Munn and Paige Dreger PHYS 112 Sec L04 Purpose: The intention of this experiment was to gain experience in measuring current, voltage and resistance in DC circuits. As well as to verify some of the basic relationships that govern purely resistive circuits, like Ohm’s Law. Lastly to examine the behavior of resistors when placed into a series and parallel arrangement. Introduction: This lab is one of the most fundamental in the study of current electricity. Ohm’s Law deals with the relationship between voltage and current in an ideal conductor. This relationship states
that for a given conductor at a given temperature the current, I through the conductor is proportional to the difference in potential, delta V, which is established between the ends of the conductor. Commonly written as: I = delta V/R where R is resistance. In this lab we worked with circuit elements for which Ohm’s Law is valid, meaning the ratio of potential difference to current is constant as the potential difference is varied. If the conductor is not Ohmic, Ohm’s Law is not valid, the ratio of delta V to I does not remain constant. Procedure: Part 1: One of the resistors was picked and the colours of the bands were recorded. The nominal value of the resistor’s resistance were recorded as 675.0 Ohms, 466.19 Ohms and 674.0 Ohms. A circuit was constructed using the single resistor, the applied emf was varied and 10 ammeter and voltmeter readings were recorded, see Figure 1. A graph of I vs delta was plotted and the value of the resistance of the resistor was determined from the slope. Part 2: Resistors R1, R2 and R3 were selected, with resistance of 675.0 Ohms, 466.19 Ohms and 674.0 Ohms. Two of the resistors were connected in series and and using the DMM the total resistance was 1.1408 k Ohms. When all three resistors were connected in series the total resistance was 1.814 k Ohms. When the three resistors were connected in series with the direct current power supply, the total delta V was recorded as 12.086 V. The potential difference across each resistor were recorded as 4.496 V, 3.105 V and 4.485 V, for R1, R2 and R3 respectively. The current leaving the power supply was measured at 6.645 mA, and the current leaving each resistor was 6.633 mA, 6.403 mA and 6.521 mA for R1, R2 and R3 respectively. Part 2.2 Two of the resistors were connected in parallel and the total resistance was measured at 275.72 Ohms, three resistors connected in parallel had a total resistance of 195.69 Ohms. The three resistors were connected in parallel with the direct current power supply, the power supply was recorded at 7.98 V. The potential difference across each resistor was recorded at 7.98 Ohms, 7.98 Ohms and 7.98 Ohms for R1, R2 and R3 respectively. The current leaving the power supply was 38.62 mA, the current leaving each resistor was 11.6 mA, 16.75 mA and 11.656 mA through R1, R2 and R3 respectively. Results: Figure 1 R delta V (amps) I 0.9513 1.41 0.6746808511 1.9819 2.937 0.674804222 2.974 4.408 0.6746823956 3.9864 5.909 0.6746319174 4.9331 7.315 0.6743814081 5.906 8.762 0.6740470212 6.922 10.274 0.6737395367 7.967 11.831 0.6734003888 8.847 13.145 0.6730315709 9.827 14.611 0.6725754568 Figure 2 Analysis: In Figure 1 the current remains roughly around 0.674 mA even though the volts and resistance increases. The current was calculated using Ohm’s law, I = delta V/R ex. 1 volt = 0.9513 volts/1.410 R = 0.674680851 aM In Figure 2 the slope of the graph is negative, the I goes down as the delta V increases. The slope of the resulting line is the value of the resistance of the resistor, which is 2.501E 4. The equation of the line is y = 2.501E 4*x + 0.675. 2.1 vi) Use Ohm’s Law to calculate the resistance of each resistor. R1 = delta V/I = 4.496 V/ 6.633 mA x 10^3 = 678 Ohms R2 = delta V/I = 3.105 V/ 6.4003 mA x 10^3 = 484.9 Ohms R3 = delta V/I = 4.485 V/ 6.521 x 10^3 = 687.8 Ohms These values for the resistance are very close to the resistance values measured earlier with the DMM, R1, R2 and R3 respectively. 2.2 v) Use Ohm’s Law to calculate the resistance of each resistor. R1 = delta V/I = 7.98 V/ 11.656 mA x 10^3 = 674.6 Ohms R2 = delta V/I = 7.98 V/ 16.75 mA x 10^3 = 476.4 Ohms R3 = delta V/I = 2.98 V/ 11.6 x 10^3 = 687.0 Ohms These values for the resistance are very close to the resistance values measured earlier with the DMM, R1, R2 and R3 respectively. Discussion: ...
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