Lab & Pre-lab #5: Voltage

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Name:Lab Partners:Date:ObjectivesLAB 5Fundamentals of Circuits III: Voltage & Ohm’s Law• Tofurtherourunderstandingoftheconceptofpotentialdifference(voltage)andtoexplainthe role of a power supply in a circuit.• To understand how potential difference (voltage) varies across the components in a circuitinvolving resistors that are connected in series.• To understand how potential difference (voltage) varies across the components in a circuitinvolving resistors that are connected in parallel.• To understand the quantitative relationship between the potential difference across aresistor and current through the resistor, and to understand the difference between componentsthat obey Ohm’s Law (Ohmic) and the components that do not obey Ohm’s Law(non-Ohmic).This lab has been adapted from the Real Time Physics Active Learning Laboratories [?].The goals, guiding principles and procedures of this labs parallel the implementation found inthe work of those authors [?, ?, ?].OverviewIn previous lab activities you examined currents through different elements in series and parallelcircuits. You saw that in a series circuit, the current is the same through all elements, and thatin a parallel circuit, the current is distributed among the branches in such a way that the totalcurrent through the battery equals the sum of the currents in each branch. You also saw thatin circuits with two or more parallel branches connected directly across a battery, making achange in one branch does not affect the current in the other branch or branches, while in seriescircuits, making a change in one part of the circuit changes the current in all parts of that seriescircuit.You also saw that connecting multiple light bulbs in series results in alarger net resistance tocurrent and therefore a smaller current results in the circuit, while adding multiple light bulbsin parallel results in a smaller net resistance in the circuit and consequently a larger current.You have also learned about electric potential difference, or Voltage, and its relationship towork. In this lab, you will establish that a battery produces an electric potential difference,and that this potential difference can cause a current in a circuit. You will then compare thepotential differences (voltages) across different parts of series and parallel circuits. In the lastpart of this lab you will explore the quantitative relationship between the current through aresistor and the potential difference (voltage) across the resistor and arrive at a mathematicalrelationship between current, voltage and resistance. When this relationship is a linear one, itis known as Ohm’s law.PHYS-204:Physics II Laboratory 1
Fundamentals of Circuits III: Voltage & Ohm’s Law v 0.1Investigation 1:Batteries and Voltages in Series CircuitsIn previous labs on the fundamentals of circuits, you developed a current model and utilizedthe concept of resistance to explain the relative brightness of bulbs in simple circuits. Yourmodel says that when a battery is connected to a circuit that provides a closed path, there is acurrent in the circuit. For a given battery, the magnitude of the current depends on the totalresistance of the circuit. In this lab you will investigate how adding batteries in series and inparallel changes the potential differences (voltages) between various points in circuits.In order to do this you will need the following items:• Computer with Logger-Pro software• Lab Pro interface• two voltage probes• Two 1.5 V D cell battery with holder• connecting wires• alligator clips• Two #14 bulbs in sockets• contact switchIn a previous lab you saw what happens to the brightness of a bulb in the circuit shown inFig. 1(a) if you add another bulb in series as shown in circuit 1(b). Neither of the two bulbs isas bright as the original bulb. Adding another bulb (resistor) to the first one in series increasedthe overall resistance in the circuit has increased, resulting in less current through the bulbs.SSS+−A+−BC+−+−BC(a)(b)(c)Figure 1: Series circuits with (a) one battery and one bulb, (b) one battery and two bulbs and(c) two batteries and two bulbs. (All batteries and all bulbs are identical.)Prediction 1.1 What do you predict would happen to the brightness of the two bulbs if youadded a second battery in series with the first at the same time that you added the second bulbas in Fig. 1 (c)? How would the brightness of bulb A in circuit 1 (a) compare to bulb B incircuit 1(c) and to to bulb C?PHYS-204:Physics II Laboratory 2
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Lab & Pre-lab #5: Voltage

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