Lab 06-Circuit Construction_updated

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Apr 3, 2024

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PHYS 2 Lab Spring 2023 umm Fall 2021er Lab Lab 06 DC Circuits By now you should have become familiar with the ‘Virtual Labs’ performed using Simulations using the Web-Links. Lab Objectives: 1. Calculating current and voltage in different parts of series/parallel resistor networks/circuits. 2. Measuring current and voltage using an ammeter and voltmeter, respectively. Introduction: In Lab #05, you investigated the relationship between voltage, resistance, and current in a simple circuit. In this lab simulation, you will design circuits that are a little more complicated. You will construct a circuit with resistors in series, in parallel , and a combination of series and parallel . In each of these constructions, you are going to predict the current flowing through a resistor as well as the voltage drop across the resistor using Ohm’s Law . We also learn using measuring instruments. An ammeter is a device used to measure the current through and is connected in series combinations in the circuit. A voltmeter is used to measure the voltage across and is connected in parallel. Series combination of resistors: Two or more resistors (it also applies to bulbs) are said to be connected in series if the same current flows through each resistor. Figure 3 shows two bulbs connected in series. In a series connection, since there will be no junctions in the circuit where the current would split, the magnitude of current passing through each resistor will be the same. The voltage drop across each resistor will, however, vary depending on the value of the resistors used. Thus , 𝑹 𝒆𝒒? = 𝑹 ? + 𝑹 ? + … . . +𝑹 𝒏 ………… (1) Where R eqv is the equivalent resistance.

PHYS 2 Lab Spring 2023 umm Fall 2021er Lab Parallel combination of resistors: Two or more resistors are said to be connected in parallel if the same voltage drop is across each resistor. Figure 4 shows two bulbs connected in parallel combination. In this combination, since there exists a junction, the current through the battery will split into two branches that contain the bulb. Hence the current across each bulb will vary depending on the resistance of the bulb. 1 𝑅 𝑒𝑞𝑣 = 1 𝑅 1 + 1 𝑅 2 + ⋯ + 1 𝑅 𝑛 ………………… (2) Simulations: Open Circuit Construction Kit: DC https://phet.colorado.edu/sims/html/circuit-construction-kit-dc/latest/circuit- construction-kit-dc_en.html Click on “ Intro ”. Take a few minutes to become familiar with the simulation. Look at th e description of different parts of the circuit on the next page. Drag different elements to make your circuit. Here are the basics of operations in the simulation: • To add elements to your circuits, simply drag an item into the work area. • To change the value of an element, click on the item. Change the value of the slider located at the bottom of the screen. • To uncouple two circuit elements, click on the circular junction and click on the scissor. • To measure current and voltage , drag the ammeter and the voltmeter respectively from the top left panel. Remember that voltage across an element is measured in parallel to the element whereas current passing through an element is measured by adding an ammeter in series. ● Write the resistance of the light bulb by clicking on it. 𝑹 𝒃?𝒍𝒃 10 Ohm ⮚ Move out of the “ Intro ” and select “ Lab ” for the rest of Lab 06 (Bottom of Screen) Note: You can view the flow of electrons or look at the conventional current. Keep the Wire Resistivity at “tiny” and the Battery Resistance at “0” – the default value.

PHYS 2 Lab Spring 2023 umm Fall 2021er Lab Different parts of the simulation you may find useful You may use the following circuit elements for this lab: Battery Light bulbs Low voltage (LV) Low resistance (LRB) High voltage (HV) High resistance (HRB) Connecting wire Resistors Low resistance ( LR ) High resistance (HR) Using Voltmeter and Ammeter An Ammeter is used to measure the current flowing through different parts of a circuit. You need to add an ammeter in series with the circuit. The figure on the right shows an ammeter connected between two resistors in series.

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PHYS 2 Lab Spring 2023 umm Fall 2021er Lab A Voltmeter is used to measure the potential (voltage) drop across a circuit element. You need to connect the voltmeter in parallel to the circuit element. The figures show a voltmeter used to measure the voltage drop across a light bulb and across a resistor. Notice that the probes are in parallel to the light bulb and to the resistor. The red probe of the voltmeter is designed to be at a higher potential. If you read a negative value in the voltmeter, just switch the probes. Lab Work: Activity 1: Connecting ammeter to measure the current passing through an element of the circuit Task 1 : Measuring current passing through each bulb when two bulbs are connected in Series Construct a circuit as shown aside. (a) Set the Value of Voltage to 10V resistance of each bulb to 10Ω and Connect the Ammeter (one like you see in “Using Voltmeter and Ammeter” section) in place of ‘Current Sensor’ and “A”, and record the value of current through each bulb below. Current across First bulb = .5 A [2 Points]

PHYS 2 Lab Spring 2023 umm Fall 2021er Lab Current across Second bulb = .5 A [2 Points] (b) Change the resistance of the second bulb to 20Ω and record the following: Current across First bulb = .33 A [2 Points] Current across Second bulb = .33 A [2 Points] Task 2 : Measuring the current passing through each bulb when two bulbs are connected in parallel With the same value settings as Task 1, set up a circuit as shown alongside above. The blue dots right next to Bulb 1 represent a switch that you need to add and control. (a) With the switch closed (i.e., current flowing through both bulbs), record the following: Current across Bulb 1: 1 A [2 Points] Current across Bulb 2: 1 A [2 Points] (b) With the switch open (i.e., current not flowing through both bulbs), record the following: Current across Bulb 1: 0 A [2 Points] Current across Bulb 2: 1 A [2 Points] (c) With the switch closed , change the resistance of Bulb 1 to 20 Ω and record the following: Current across Bulb 1: .5 A [2 Points] Current across Bulb 2: 1 A [2 Points] Follow-up Questions: (i) In Task 1 (a) and (b), How are the currents related? [2 Points] They are the same between the two bulbs (ii) Derive the value of current/s you obtained in Task 1 (a) and (b) theoretically using the concept of resistor in series and Ohm’s law. [2+2 = 4 Points] I = V/R 10/20 = .5

PHYS 2 Lab Spring 2023 umm Fall 2021er Lab 10/30 = .33 (iii) How did the current change between Task 2 (a) and (b)? [2 Points] The current change because the switch was open or closed. When it was closed bulb 1 was in a closed circuit but when the switch was open it was not in a closed circuit so the current became 0. (iv) How did the current change between Task 2(b) and (c)? [2 Points] The major change between B and C was the switch was closed so bulb 1 gets current and the resistance of the light bulb increases which is why the current is less than A. (v) Derive the value of current/s you obtained in Task 2(a), (b), and (c) theoretically using the concept of resistors in parallel and Ohm’s law. [2 + 2+ 2 = 6 Points] A) I = 10/10 = 1A I = 10/10 = 1A B) I = 0/10 = A I = 10/10 = 1A C) I = 10/20 = .5A I = 10/10 = 1A Activity 2 : Connecting Voltmeter to measure Voltage across an element of the circuit Task 3 : Measuring the voltage across each bulb when two bulbs are connected in Series Construct a circuit as shown below on the right side.

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PHYS 2 Lab Spring 2023 umm Fall 2021er Lab (a) Set the value of the Voltage to 10V, and the resistance of each bulb to 10Ω and connect a Voltmeter (one like you saw in the “Using Voltmeter and Ammeter” section) across Bulb 1 and record the voltage. Now move the voltmeter to Bulb 2 and record the voltage. Voltage across First bulb = 5 V [2 Points] Voltage across Second bulb = 5 A [2 Points] (b) Change the resistance of second bulb to 20Ω and record the following: Voltage across First bulb = 3.33 V [2 Points] Voltage across Second bulb = 6.67 V [2 Points] Task 4 : Measuring voltage across each bulb when two bulbs are connected in parallel With the same values settings as Task 1, set up a circuit as shown alongside. (a) Record the following: Voltage across Bulb 1: 10 V [2 Points] Voltage across Bulb 2: 10 V [2 Points] (b) Now, change the resistance of Bulb 1 to 20 Ω and record the following: Voltage across Bulb 1: 10 V [2 Points] Voltage across Bulb 2: 10 V [2 Points] Follow-up Questions: (i) In Task 3 (a), how are voltages across two bulbs related? [2 Points] They are the spread the same between the 2 bulbs (ii) In Task 3 (b), how does the voltage differ compared to 3(a) across both bulbs? [2 Points]

PHYS 2 Lab Spring 2023 umm Fall 2021er Lab The voltage is split unevenly between 2 bulbs but it add back to the voltage of the battery (iii) Derive the value of voltages you obtained in Task 3 (a) and (b) theoretically using the concept of resistor in parallel and Ohm’s law. [2 + 2 = 4 Points] A) I = 10/20 =.5 V1 = .5*10 =5 V2 = .5*10 =5 R = 10+10 = 20 V = 5+5 = 10 B) I = 10/30 =.33 V1 = .33*10 =3.33 V2 = .33*20 =6.67 R = 10+20 = 30 V = 3.33+6.67 = 10

PHYS 2 Lab Spring 2023 umm Fall 2021er Lab Activity 3: Measuring current and voltage across circuit elements in a mixed circuit. Construct a circuit, as shown above, paste a screenshot [2 Points] of the circuit below and complete the following table: [14 Points] R1 R2 R3 R4 R5 R6 R7 Current .5 .25 .25 .25 .12 .13 .12 Voltage 2 1 2 2.5 .5 .25 .25

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PHYS 2 Lab Spring 2023 umm Fall 2021er Lab Calculate the current and voltage across resistor R1 and R2 theoretically. Show your work to get full credit. [3 + 3 = 6 Points + 5 points bonus it all correct!] [Hint: The following video link will help you how to proceed for calculations: [ https://www.youtube.com/watch?v=nqS-gHq2Ylo ] R67 = 2+2 =4 ohm R23 = 4+8 = 12 ohm

PHYS 2 Lab Spring 2023 umm Fall 2021er Lab R567 = (1/4+1/4)^-1 = 2 ohm R4567 = 2+10 =12 ohm R234567 = (1/12+1/12)^-1 = 6 ohm Rt = 6+4 = 10 ohm V = 5V I = 5/10 = .5 A V1 = .5*4 = 2V V2 = .5/2*4 = 1V