Series and Parallel Circuits 1 Lab - University of Michigan



SERIES AND PARALLEL Circuits – IUM Physics Demo Lab 07/2013Pre-Lab QuestionWhat is the difference between voltage and current? Use the flow of water in a pipe as an analogy.EXPLORATIONMaterials1 green multimeter (with leads)1 battery board1 alligator lead card1. Build the circuit shown in the schematic below. The numbers indicate contact points where you will use the multimeter probes to measure voltage. Build the 6V battery from 1.5V cells.Figure SEQ Figure \* ARABIC 1: A Simple CircuitMeasure the voltage across the battery. Although the cells are labeled 1.5V, the actual cell voltage may vary. The actual voltage can be greater than 1.5V for brand new cells, and less than 1.5V for cells that have been used. It is alright if the voltage is not exactly 6V for the assembled battery. To measure the total battery voltage, be sure to measure from bottom-to-top for the combined cells.Actual Battery Voltage: Number of Cells: _______________ 2. First, predict the voltages (V) you will measure between the labeled points on the circuit. Close the switch, and measure the voltages. Place the probes at contact points shown on the circuit diagram above and record below. Second, measure the current at each of the three points. To measure, you interrupt the circuit with the multimeter which means you disconnect the circuit at a point and use the multimeter to complete the circuit. Measure the current at the test points with the meter set to milliamperes (mA) and record below. Contact PointsPredictedMeasuredExplanation of Prediction and MeasurementV1-2V2-3V1-3I1XI2XI3XExplain your observations. How does the voltage across the light bulb compare to the battery voltage? Does current behave differently than voltage in a circuit and how? Series Circuits3429000-40005003. Build the circuit drawn in the schematic below. Predict the voltage for each pair of test points. Measure the voltages and record below.Predict whether the measured currents will be greater, smaller or the same as you measured for a single bulb in the simple circuit of Figure 1. Measure the current at each point and record.Figure SEQ Figure \* ARABIC 2: A Series CircuitContact PointsPredictedMeasuredExplanation of PredictionV1-2V2-3V1-3I1I2I3Explain your observations. How do light bulbs in series share voltage? How does this compare to the voltage of the battery? Why are they the same or different? How does the current compare to that of the single-bulb circuit and why is it the same or different?Parallel Circuits4. Build the circuit shown below.Figure 3: A Parallel Circuit5.Predict what the voltage will be across each light bulb when you close the switch. How does this compare with the total potential of the battery? Discuss with your group. After recording your prediction, close the switch and measure the voltages across the two light bulbs. Explain what you observe.Based on the current you measured for a single light bulb in the simple circuit of Figure 1, predict the current for each bulb and for the whole circuit (test points a, b, and c). Discuss with your group and explain your prediction. Will current behave the same as with two bulbs in series? Measure the current at points a, b and c and compare with your prediction.Contact PointsPredictedMeasuredExplanation of PredictionV1-4V2-3IaIbIcExplain your observations. How do voltage and current behave in a parallel circuit compared to a series circuit? Power6. Fill in the table below with the values for voltage and current you measured for a series circuit of two bulbs at 6V (Figure 2) and a parallel circuit of two bulbs at 6V (Figure 3) Calculate and compare the power consumed by each of the bulbs. Recall from the circuits lab: (Power = Current x Voltage)BulbCurrentVoltagePower1 of 2 in series2 of 2 in series1 of 2 in parallel2 of 2 in parallelChallenge Work: 1. Describe a fast way to check if a light bulb circuit is series or parallel, without tracing the circuit.2. (Series) Using the series circuit, remove one battery from the circuit by re-wiring. How did this change the brightness of the bulbs? How does the voltage of the batteries affect the brightness of the bulbs?3. (Parallel) Why do you think most Christmas tree lights are wired in parallel?4. Which circuit, Figure 2 or Figure 3, consumes more power from the battery? Justify your claim by calculating the power consumed by the circuit in each case.Summary:The total voltage available to a circuit is determined by the number of cells in series for the source battery.The electric force in a DC circuit is conservative, like gravity.The sum of the component voltages in a series circuit is equal to the voltage of the source (Kirchhoff’s Loop Rule). The Loop Rule results from the conservative nature of the electric force and is equivalent to the statement that the electric force does no net work over a closed loop path, exactly the same as for gravity. Equivalently, the sum of the voltages around any closed loop in a circuit must be zero.The current is the same throughout each element of a series circuit.The current is inversely proportional to the number of resistors (bulbs) in the circuit (a consequence of Ohm’ Law).The current divides in a parallel circuit, but the total current must be conserved (continuity, charge conservation and the Junction Rule for electric current).The voltage across each component in a parallel circuit is the same and equal to the source voltage. This implies that the voltage across each element in a series circuit is less than that for a parallel circuit for the same source potential (battery voltage). Power/brightness is the product of the voltage across a bulb and the current flowing through it.Final Clean-upPlease disconnect all alligator leads and reattach them to the clip card. Replace all equipment to the carts. Voltage and CurrentCurrent and voltage are the two quantities used to describe the behavior of electricity in a circuit.VoltageThe total electric potential (“voltage”) across a circuit cannot exceed the voltage of the power source (battery). The power source provides stored electrical energy ready to power a circuit. Voltage, like pressure in a fluid, is applied across two points in a circuit. Voltage does not “flow through a circuit”.The voltage across a single component depends on three factors: the component itself (the electrical resistance of the component), the resistance of all the other components in the circuit, and the total voltage of the power source. When you measure the voltage across a light bulb (a device with resistance) the voltage is high. When you measure the voltage across a length of wire (very low resistance), the voltage is very low. Ohm’s Law relates current, voltage and resistance.CurrentCurrent is the flow of electric charge from one point to another within a circuit.Current depends on the electric potential of the power source and the challenge the circuit presents to the flow of current known as electrical resistance. The current is the same at any point in a series circuit. The current is not the same everywhere in a parallel circuit; it divides between the parallel paths.Current is a conserved quantity. Thus, in a parallel circuit the total current at the source (the positive pole of the battery) is equal to the sum of the current flowing in all the parallel branches:This of course must also be the total current returned to the negative pole of the battery. ................
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