Building Circuits MEASURING VOLTAGE AND CURRENT

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1 uilding ircuits In this experiment you will construct several circuits and use Ohm s Law to compare the current, resistance, and voltage in series and parallel circuits. GETTING STTED. Go to and log in using your Username and Password. 2. Select rowse Gizmos icon at the upper left. Select Grades 9 2 Physics Select Electricity and Magnetism Select dvanced ircuits and Launch the Gizmo. 3. To build a simple circuit with a single bulb and battery, use the cursor to drag a battery, two wires, and a bulb. Notice the light bulb glows. The slider at the bottom of the circuit board adjusts the voltage. 4. emove one of the wires and replace it with a switch. Turn the switch on and off. MESUING VOLTGE ND UENT. uild a simple circuit with one bulb, one battery, a switch and a wire. Set the voltage to 0 volts. 2. Using the cursor, drag the positive terminal of the volt meter to the positive side of the bulb and the negative terminal of the meter to the negative side of the bulb. The voltage in the circuit is displayed at the bottom left of the Gizmo. The voltmeter must be placed across the bulb. (see diagram to the right) 3. Using the cursor, drag the ammeter and place it near one of the connections in the circuit. The current (in amperes) is displayed below the voltage. The ammeter must be placed in series with the bulb. (see diagram to the right) Part I: Series ircuits. onstruct a circuit with two bulbs in series. Measure the overall voltage in the circuit by placing the appropriate terminal of the voltmeter at the terminals of the battery. Measure the voltage across each bulb. Next, place the ammeter in the circuit to determine the current at the designated points within the circuit. Draw your circuit in the box, label each bulb ( & ). ecord your data below. (cross) 5.0 V etween & 5.0 V etween ulbs & 0.0 V etween & urrent onstruct a circuit with three bulbs in series and measure the voltage and current as you did above. (cross) 3.33 V etween and 3.33 V etween & ulb 3.33 V etween & 0.0 V etween and urrent 0.22 O uilding ircuits

2 ompare the voltage across the battery (total voltage) and the voltage at each bulb for the two circuits. Write a generalized statement that describes the relationship between the total voltage and the voltage at each bulb. The sum of the voltage across each bulb totals the total voltage in the circuit. ompare the current at the battery (total current) and the current at each bulb. Write a generalized statement that describes the relationship between the total current and the current at each bulb. The current is the same throughout the circuit. 3. Using Ohm s Law ( V = I ), calculate the resistance in Ohms at the various points within the circuit. The unit for resistance, Ohm, is symbolized by the Greek letter omega (Ω). ulb 5. Ω 5. Ω 30 Ω 5. Ω 5. Ω 5. Ω 45.5 Ω 4. econstruct the series circuit with two bulbs without a battery. To check the total resistance in the circuit, place the Ohmmeter where the battery would normally be located. The Ohmmeter will only function when there is no current running through the circuit. Then, reconstruct the series circuit with three bulbs and check the total resistance and the resistance of each bulb. ulb 30 Ω 45 Ω Write a generalized statement that describes the relationship between the total resistance in the circuit and the resistance at each bulb. The total resistance in a circuit is the sum of the resistances at each bulb. How does the total resistance in a series circuit change when increasing the number of bulbs? Increasing the number of bulbs increases the total resistance. Does the resistance of each bulb change when increasing the number of bulbs in the circuit? The resistance of each bulb is the same regardless of how many bulbs are in the circuit. Part II: Parallel ircuits. onstruct a circuit with two bulbs in parallel. Measure the overall voltage in the circuit and across each bulb. hange the placement of the ammeter in the circuit to determine the current at several points within the circuit. Draw the circuit and record your data below. 0.0 V 0.0 V 0.0 V Near the Near Near urrent uilding ircuits 2

3 2. onstruct a circuit with three bulbs in parallel. Draw the circuit, measure and record the voltage and current in the circuit. cross cross cross ulb cross 0.0 V 0.0 V 0.0 V 0.0 V Near Near Near ulb Near the urrent ompare the voltage across the battery (total voltage) and the voltage at each bulb for the two circuits. Write a generalized statement that describes the relationship between the total voltage and the voltage at each bulb. The voltage is the same anywhere in the circuit. ompare the current at the battery (total current) and the current at each bulb. Write a generalized statement that describes the relationship between the total current and the current at each bulb. The total current is the sum of the currents at each bulb. 3. s you have seen, the total current in a parallel circuit, I, is equal to the sum of currents in each parallel branch: IT = I I2 I3 Using Ohm s Law ( V = I ), calculate the resistance for each bulb in the two circuits and the total resistance in the circuit. ulb 7.5 Ω 5.0 Ω 4. econstruct the parallel circuit with two bulbs without a battery. To check the total resistance in the circuit, place the Ohmmeter where the battery would normally be located. The Ohmmeter will only function when there is no current running through the circuit. Then, reconstruct the parallel circuit with three bulbs and check the total resistance and the resistance of each bulb. ulb 7.5 Ω 5.0 Ω How does the total resistance in a parallel circuit change when increasing the number of bulbs? Does the resistance of each bulb change when increasing the number of bulbs in the circuit? Increasing the number of bulbs in a circuit decreases the total resistance in the circuit. The resistance of the bulb does not change when placed in either a series or parallel circuit. uilding ircuits 3

4 5. The total resistance of a parallel circuit can also be found using the equivalent resistance equation, where the total resistance in a parallel circuit t can be calculated from the following formula: t =... Substitute the values for the resistances of each bulb and calculate the total resistance in each parallel circuit. for Two Parallel ulbs / t = / 5 / 5 = 2 / 5 = / 7.5 t = 7.5 Ohms for Three Parallel ulbs / t = / 5 / 5 / 5 = 3 / 5 = / 5 t = 5.0 Ohms ( in the circuit decreases when additional bulbs are placed in the circuit.) Part III: uilding ompound ircuits In this part, you will build several examples of compound circuits that combine parallel and series components.. uild the circuit shown in the diagram to the right. This circuit should look familiar since it is the compound circuit that was constructed in the previous laboratory. Set the voltage of the battery to 0.0 V. Notice that bulbs & are in series, and that bulbs & are parallel with bulb. s you have concluded from the previous experiments: FO SEIES IUITS: The total voltage in the circuit is the sum of the voltages across each bulb. The current is the same anywhere in the circuit. The total resistance in a circuit is the sum of the resistances at each bulb. FO PLLEL IUITS: The voltage is the same anywhere in the circuit. The total current is the sum of the currents at each bulb. The total resistance of a circuit follows the relationship: = t Use the voltmeter and ammeter to determine the voltage and current at each bulb,, &. Then, use Ohm s Law to calculate the resistance of each bulb. ecord your values below. ulb urrent 5.0 Ω V 5.0 Ω V 5.0 Ω V uilding ircuits 4

5 3. Using the information from the table above, determine the total current, voltage, and resistance in the compound circuit. urrent at at urrent: dd currents in each branch: = V 0.0 Ω : at battery is same as bulb. : Use equivalent resistance equation for resistances of each branch: /30 /5 = /30 2/30 = 3/30 = /0 t = 0 Ω 4. The power of a light bulb, measured in Watts, is determined by the following equation: Power = urrent x or P = I V alculate the power (in Watts) for each of the bulbs in the circuit diagram and record your answers in the data table above. ulb Power.65 W.65 W 6.70 W 0.0 W onstruct a statement that relates the power of the bulb to its apparent brightness. The greater the Wattage the brighter the bulb. Part II: uilding ompound ircuits (continued). uild the circuit shown in the diagram to the right. This compound circuit was also constructed in the previous laboratory. Set the voltage of the battery to 0.0 V. How many pathways for the current are there in the compound circuit and which bulbs do they contain? ulbs, & D ulbs & D 2 Use the voltmeter and ammeter to determine the voltage and current at each bulb,,, & D. Then, use Ohm s Law to calculate the resistance of each bulb. ecord your values below. ulb urrent 2.0 V Ω 2.0 V Ω D 4.0 V Ω D 6.0 V Ω urrent at at V 25.0 Ω 3. Using the information from the table above, calculate the total current, voltage, and resistance in the compound circuit. Then calculate the power at each light bulb. ulb ulb D Power 0.26 W 0.26 W.04 W 2.40 W 3.96 W uilding ircuits 5

6 POST LOTOY POLEMS Without using the computer simulation, determine the missing values in the data tables for each of the following circuits. fterwards, build the circuit and test your answers using the ammeter, voltmeter, and Ohmmeter. ulb urrent Power 5.0 V Ω.65 W 5.0 V Ω.65 W ircuit 5.0 V Ω.65 W D 5.0 V Ω.65 W 0.0 V Ω 6.6 W D ircuit 2 ulb urrent Power 4.0 V Ω.0 W 2.0 V Ω.0 W 2.0 V Ω.0 W D 4.0 V Ω.0 W 0.0 V Ω 4.0 W D ircuit 3 ulb urrent Power 4.28 V Ω.35 W.43 V Ω 0.5 W.43 V Ω 0.5 W D.43 V Ω 0.5 W D E 4.28 V Ω.35 W 0.0 V Ω 3.5 W E uilding ircuits 6

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