COMPOUND CIRCUITS. Voltage (volts) Across Bulb B. Across the Battery. Across Bulb A. Current (amperes) Between A & B. Between Battery & B

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1 OMPOUN IUITS LOGGING ON Go to and log in using your Username and Password. Select rowse Gizmos icon at the upper left. Select Grades 9 2 Physics Select Electricity and Magnetism Select dvanced ircuits and Launch the Gizmo. GETTING STTE 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. emove one of the wires and replace it with a switch. Turn the switch on and off. MESUING VOLTGE N 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) PT I: SEIES IUITS onstruct a circuit with two bulbs in series. Set the voltage to 0.0 volts. 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. ecord your data in the tables. cross ulb Voltage (volts) cross ulb cross the attery attery & urrent (amperes) & attery & uilding ircuits

2 onstruct a circuit with three bulbs in series and measure the voltage and current as you did above. Voltage (volts) cross ulb cross ulb cross ulb cross the attery urrent (amperes) attery & & & attery & 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 for a series 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. LULTING ESISTNE Using Ohm s Law ( V voltage = I current x resistance ), 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). Express your answers to 3 significant figures. ulb ulb attery ulb ulb ulb attery uilding ircuits 2

3 MESUING ESISTNE econstruct the series circuit with two bulbs without a battery. The Ohmmeter will only function when there is no current running through the circuit. To check the total resistance in the circuit, place the Ohmmeter where the battery would normally be located. Then, place the Ohmmeter at opposite terminals for each bulb to measure the resistance of the bulb. Then, reconstruct the series circuit with three bulbs and check the total resistance and the resistance of each bulb. ulb ulb Total ulb ulb ulb Total Write a generalized statement that describes the relationship between the total resistance in the circuit (as measured where the battery would be located) and the resistance at each bulb. How does the total resistance in a series circuit change when increasing the number of bulbs? oes the resistance of each bulb change when increasing the number of bulbs in the circuit? PT II: PLLEL IUITS onstruct a circuit with two bulbs in parallel and set the voltage to 0.0 volts. 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. ecord your data in the tables. cross ulb Voltage (volts) cross ulb cross the attery attery & urrent (amperes) & attery & uilding ircuits 3

4 onstruct a circuit with three bulbs in parallel and measure the voltage and current as you did above. cross ulb cross ulb Voltage (volts) cross ulb cross the attery urrent (amperes) attery & & & attery & 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. 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. LULTING ESISTNE Using Ohm s Law ( V = I ), calculate the resistance for each bulb in the two circuits. ulb ulb ulb ulb ulb LULTING TOTL ESISTNE FO PLLEL IUITS The total resistance of a parallel circuit can also be calculated using the equivalent resistance equation, where the total resistance in a parallel circuit TOTL can be calculated from the following formula: t... s you have seen, the total resistance in a series circuit increases as the number of bulbs increases, for a parallel circuit, the total resistance decreases as more bulbs are added. uilding ircuits 4

5 Using the equivalent resistance equation, substitute the values for the resistances of each bulb and calculate the total resistance in each parallel circuit. Show your work below. (Hint: educe the fraction rather than calculate.) Total esistance for Two Parallel ulbs Total esistance for Three Parallel ulbs How does the total resistance in a parallel circuit change when increasing the number of bulbs? PT III: UILING OMPOUN IUITS 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 in each circuit. The total resistance of a circuit follows the relationship: t... uilding ircuits 5

6 Use the voltmeter and ammeter to measure the voltage and current at each bulb,, &. ecord your values in the table. ulb esistance (Ohms) urrent (amperes) Voltage (volts) Use Ohm s Law to calculate the resistance for each bulb. Total ETEMINING TOTL ESISTNE, UENT & VOLTGE Using the information from the table above, you will next determine the total current, voltage, and resistance in the compound circuit. To determine the total current:. Use the series rule for current for the right-hand circuit (bulbs & ). urrent is the same in both bulbs. 2. Use the parallel rule for current for the entire circuit (right and left hand): Total current is the sum of the currents in each circuit. Total urrent = + (bulbs & ) (bulb ) To determine the total voltage:. Use the series rule for voltage for the right-hand circuit. Voltage in circuit is the sum of voltages in the bulbs. 2. Use the parallel rule for voltage for the entire circuit (right and left hand). Total voltage is the same as the voltage in each circuit. Total Voltage = To determine the total resistance:. Use the series rule for the resistance for the right-hand circuit: The resistance in this circuit is the sum of the resistances for bulbs & ight-hand circuit resistance = 2. Use the Equivalent esistance ule for the entire circuit (right and left hand). / total = / right hand + / left hand TOTL = uilding ircuits 6

7 LULTING POWE The power of a light bulb, measured in Watts, is determined by the following equation: Power (Watts) = urrent (mperes) x Voltage (Volts) or P = I V alculate the power (in Watts) for each of the bulbs in the circuit diagram ulb ulb ulb onstruct a statement that relates the power of the bulb to its apparent brightness. UILING OMPOUN IUITS (ONTINUE) Examine the circuit shown in the diagram to the right. How many different pathways are there for the current in the compound circuit? Which bulbs does each circuit contain? Left Side: ight Side: re the bulbs in each circuit in series or parallel with each other? re the two pathways (Left and ight Side) in series or in parallel with each other? Notice that some of the values have been included in the table below. The first step in determining the missing values is to assess which bulbs in the circuit are identical to each other. Then, information which is known concerning one bulb can added to the information known about similar bulbs. Using this information fill in the missing data without constructing the circuit. Then, calculate the total current, voltage, and resistance in the compound circuit. Now, construct and test the circuit using the voltmeter and ammeter to determine the voltage and current at each bulb to confirm your solution. Finally, calculate the power (in Watts) at each light bulb. Power (Watts) ulb ulb ulb ulb ulb Voltage (Volts) 5.0 urrent (mperes) 0.33 esistance (Ohms) 5 Total uilding ircuits 7

8 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. emember to first assess which bulbs in the circuit are identical to each other, then the missing information can be determined from similar bulbs. ircuit ircuit ulb Voltage urrent esistance V 5 Ω Total 0.0 V ircuit 2 ircuit 2 ulb Voltage urrent esistance Power V 5 Ω E 4.28 V E Total ircuit 3 ircuit 3 ulb Voltage urrent esistance Power V 6.0 V 5 Ω Total uilding ircuits 8