Physics 2020 Lab: DC Circuits III page 1 of 6Lab: DC Circuits IIIINTRODUCTION:This week we will continue with DC circuits. In order to fully understand any circuit,you need to take into account both voltage and current. We will again be using thecomputer simulation Circuit Construction Kit (CCK) instead of real wires, bulbs, andresistors. The goals of this lab are to complete ourunderstanding of how voltage, current, and resistance relateto each other in circuits.PRECAUTIONS & NOTES:To measure how much current is flowing through acircuit, the current needs to flow through the ammeter.Recall that when we measured voltage differences, weattached the voltmeter in parallel with whatever we weremeasuring. To measure current, the ammeter needs to beplaced in series with the element (resistor, bulb, battery)that we are measuring.PART I: COMPUTING THE RESISTANCE OF A LIGHT BULBBuild a circuit consisting of a 30 V battery in series with a 15 resistor and one lightbulb. (Right-click on the battery to set its voltage.Right-clicking on the resistor to set its resistance.)Using the voltmeter with needle probes, measurethe voltage difference VBATT across the battery, thevoltage difference VR across the 15 resistor, andthe voltage difference VBULB across the light bulb.Using Ohm's Law and the known resistance of theresistor, compute the current IR flowing though theresistor.Now set up the ammeter to directly measure the current IR flowing though the resistor.Does this value match the calculated IR from the previous step?University of Colorado at Boulder, Department of PhysicsAmmeter configured to measurecurrent.R =15 30 VPhysics 2020 Lab: DC Circuits III page 2 of 6How is the current flowing though the light bulb (IB) related to the current flowing throughthe resistor (IR)? What is the relationship between the three measured voltagedifferences VR, VBULB, and VBATT?From these measurements, compute RBULB. Using the measurements and calculations from this section, how much power isdissipated in the 15 resistor? How much power is dissipated in the light bulb?PART II: ADDING A RESISTOR IN SERIESDrag and drop two light bulbs and a R=2 resistor onto the stage.Construct the circuit shown on the right, consisting oftwo identical light bulbs in series with a 20V battery.(The R=2 resistor will be added later.) Measure the voltage difference across the battery,then put the ammeter in the circuit so that you canmeasure the current flowing through the battery.Measure and record the battery voltage Vbatt andcurrent Ibatt. University of Colorado at Boulder, Department of PhysicsPhysics 2020 Lab: DC Circuits III page 3 of 6Predict what will happen to the current Ibatt flowing through the battery when you placethe R = 2 resistor in parallel with bulb 2 as shown. Will the battery current increase,decrease, or remain constant? Explain your reasoning.Now add in the R = 2 resistor, and describe what happens. Was your predictioncorrect? What happens to the brightness of bulb 1 and why? What happens to thebrightness of bulb 2 and why? PART III: 2 BULBS IN SERIESConstruct the circuit shown at right, containing a single lightbulb. Set the battery voltage to 20 V. With the voltmeter,measure the voltage difference across the light bulb. Then usethe ammeter to measure the current. Record your results.Predict what will happen if a second bulb is added in series with thefirst bulb, as shown at right. Will the brightness of the 1st bulbchange? Will the current change? Will the voltage across the firstbulb change? How will the power from the battery change, if at all?Clearly explain your reasoning.University of Colorado at Boulder, Department of PhysicsPhysics 2020 Lab: DC Circuits III page 4 of 6Now add a second bulb to the circuit in series with the first bulb. Measure the voltagedifference across each bulb and record the result. Using the ammeter, measure thebattery current and record the result. Do these results match your predictions? PART IV: 2 BULBS IN PARALLELConstruct the circuit shown at right, containing a single lightbulb. Set the battery voltage to 10 V. Measure the voltagedifference across the light bulb and the battery current. Recordyour results.Predict what will happen if a second bulb is added in parallelwith the first bulb, as shown at right. Will the voltage acrossthe first bulb change? Will the brightness of the first bulbchange? Will the current flowing through the first bulbchange? Will the current through the battery change?Clearly explain your reasoning.University of Colorado at Boulder, Department of PhysicsPhysics 2020 Lab: DC Circuits III page 5 of 6Now add a second bulb to the circuit in parallel with the first bulb. Compare with yourpredictions.Measure the battery current, and the currents flowing through each of the bulbsindividually. Record your results here. How are these three measurements related?PART V: FOUR BULB CIRCUITDo not build the following circuit. First, rank the brightness of the identical bulbs A, B, C,and D in order from brightest to dimmest BEFORE the break in the circuit is made(circuit a).What happens to the brightness of each bulb (A, B, C, and D) AFTER the break ismade? Does each bulb get brighter, dimmer, or stay the same? Explain yourreasoning.University of Colorado at Boulder, Department of PhysicsPhysics 2020 Lab: DC Circuits III page 6 of 6Build the circuit now and test your prediction. Set the battery voltage to 30 V. Add aswitch where the “break” appears. Were your predictions correct?POTENTIAL EXAM QUESTIONS:1. Which of the following statements is/are true about the following circuits? Assumeall batteries and all bulbs are identical.a) Bulb A does not turn on, because the voltage difference across it is zero.b) Bulb B does not turn on, because the voltage difference across it is zero.c) Bulb C does not turn on, because the current flowing through it is zero.d) Answers (a) and (b) are both true.e) Answers (a), (b), and (c) are all true.2. What is the correct order for the total power dissipated in the following circuits, fromleast to greatest? Assume
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