Sasha Cruz Lab 9 Ohm's Law QMPHYS1115 Rev11.30.2023

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Laredo College *

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1115

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Electrical Engineering

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Jan 9, 2024

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Lab 9: Ohm’s Law © 2023 by Orlando Patricio adapted from https://phet.colorado.edu/en/simulations/category/physics Name: Sasha Cruz INSTRUCTIONS: (1) Download this lab document, CLICK on “ enable editing ” located at the top, middle of the downloaded document and type out answers on the space provided for then save your answers. (2) If the spacing automatically moves, adjust so that your answers are not all over the place. (3) Upload this document, with your answers on it, on the designated Lab 9 Dropbox on Canvas Lab Reports/Module Tab. (4) If possible, ALL answers must be in green font or highlighted in yellow background with black font . Grading Policy for Lab Reports WITH Pre-/Post-lab Questions Grading Policy for Lab Reports WITHOUT Pre-/Post-lab Questions Completeness and accuracy of answers (with required screenshots) for the: 1. Warm-up and lab activities – 70% 2. Pre-/Post-lab questions – 10% 3. Conclusions and real-life applications – 20% Completeness and accuracy of answers (with required screenshots) for the: 1. Warm-up and lab activities – 80% 2. Conclusions & real-life applications – 20% This lab uses the Ohm’s Law simulation from PhET Interactive Simulations at University of Colorado Boulder under the CC-BY 4.0 license. Purposes/Objectives: In this lab, you will be able to: 1) explore the relationship between voltage, current, and resistance in simple electric circuit. 2) relate the slope of voltage versus current ( V vs. I ) to the resistance of a wire. 3) differentiate series and parallel circuit connections. Procedure: A. Electric circuit basic concepts: Ohm’s law: Current, I or electric charges flowing through a resistor (with resistance, R ) is directly proportional to the potential (voltage, V ) applied across it. Mathematically, ? = ? × ? or I = V / R or R = V / I Series connection: Cells are joined end to end in a series connection. Positive terminal of a cell is connected to negative terminal of the next cell. B. Develop your understanding: 1) Click the link below (hover mouse on the link then press at the same time: ctrl and left click )

https://phet.colorado.edu/sims/html/ohms-law/latest/ohms-law_en.html 2) Once Ohm’s law PhET Sim opens, your screen should look like the one below. 3) Explore using the sliders for voltage and resistance. The control panels are located on the right side of the lab area. The circular orange button at the bottom right corner is the Reset button. What did you discover? Write your answers below. Also, paste below screenshot to support your answers. 4) Select a value of resistance (say 416 ohms,  or so). Now, increase the (electric) potential or voltage (say, 4.5 V) across resistor. How does current change? The mA unit for current means milliampere. Milli means 1/1000 or 10 -3 . Write your answer below. After experimenting with all of the switches, I observed that the voltage and flows increase or decrease in tandem The current stayed the same number 0.0107A

5) Hit the Reset button. Select a value of the (electric) potential or voltage. Now, increase resistance. How does the current change? Write your answer below. 6) If a battery of 9.0 volt is connected across resistor of 1000 ohms, what will be the value of current flowing through the circuit? Write your answer below. 7) For a resistor (resistance) of 173 ohms or so, apply five different (electric) potentials or voltages then measure the current through the resistor. Read the current this way: If you have a current of 8.7 mA or 0.0087 A, this needs to be recorded in the Data Table as 0.0087. Divide the current reading by a thousand and express units as A or Ampere or Amp. Potential or Voltage (Volt) 1.5 3.0 4.5 6.0 7.5 Current (Amp) 0.0087 0.0712 (0.0259 .0345 0.0431 Plot Potential ( ? ) vs. Current ( ? ) curve on graph paper or Excel Spreadsheet. Paste the graph below inside the (box) space. Hint in creating a graph using Excel spreadsheet: To create/plot a graph of Potential vs. Current. (a) open an Excel spreadsheet, (b) type in the cells, current (Amp) for the first column and voltage or potential (Volt) for the second column and the corresponding data points, (c) highlight all entries, (d) click insert then click on insert scatter (X, Y) located above Charts at the middle top of the control panels, (e) on the drop-down menu that appears, click on the first selection composed of dots alone, (f) on the graph that appears, click on the title and edit to become Potential vs. Current Graph or Voltage vs. Current Graph , (g) right click on any of the plots or dots, (h) on the drop-down menu, select Add Trendline , I chose 4.4 as the estimation of potential and expanded the protection from 721. The current diminished as I expanded the obstruction. 0.0092A

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(i) on the right side of the screen, the Format Trendline appears, select Linear , check off set-intercept to 0.0 , check-off Display Equation on Chart , (j) on the graph, edit the equation that shows, change y to Voltage, x and change x to Current , (k) click on the “ +” sign located at the top right corner of the graph, check-off Axis Titles , (l) click on the Axis Title at the bottom of the graph and change it to Current (Amp) , (m) click on the Axis Title at the left side of the graph and change it to Voltage (Volt) , (n) click the inside part of the graph then right click and select copy , (o) open this lab document and paste the graph below these instructions, (p) on Excel spreadsheet, highlight the all data points then right click and select copy , (q) on the lab document, paste the data table before or next to the graph, (r) edit all entries as needed. Piggyback to Lab 2 about graphing using Excel spreadsheet, if you need help or ask your lab instructor/professor. 8) D etermine the slope of this graph from the results of the graph. How does this slope relate with resistance? Paste the created graph here. If you cannot paste the graph here, then DESCRIBE completely the graph you plotted including the SLOPE of the graph which is equal to the (electric) RESISTANCE value . The slope is 173.98 and the ohms is the resistance of the wire

9) If the value of resistance were 288 Ohms or so instead of 173 Ohms (or so), how will this slope change (steeper or less steep slope)? Why? C. Making connections – Ammeter and Voltmeter: 10) Click the link below (hover mouse on the link then press at the same time: ctrl and left click ) https://phet.colorado.edu/sims/html/circuit-construction-kit-dc/latest/circuit-construction-kit- dc_en.html 11) Open the Lab tab on PhET sim. You see on the screen the raw materials to create a circuit. Take a moment to look over this site and find all the different materials. To build a circuit you will need several wires, light bulbs, resistors, voltage source, voltmeter, and ammeter. Drag and drop them into the lab area then connect the parts. Play with circuit elements to see how to grab and manipulate these tools including assembling a simple circuit. Remember to put a check mark on the Show Current , Labels , and Values on the control panel located at the top right corner of the lab area. Tap a resistor. When a slider window shows at the bottom of the screen, adjust the resistance as desired. Your screen may look like the one below for a series circuit. Pay close attention to the way voltmeter and ammeter were connected. Flip the polarity If the value of resistance were 288 Ohm it has a much higher slope instead of the 173 Ohm since it is a higher value

(terminal) of the voltmeter if the voltmeter reading displays a negative voltage. The negative terminal of the voltmeter must be connected close to the negative terminal of the battery while the positive terminal of the voltmeter with the positive end of the battery. The voltmeter is connected across or parallel to a circuit element while an ammeter is connected in series. To complete the circuit, the red circles at the end of each circuit element must overlap. Please note that the light bulb also has TWO circles. Your circuit is complete and working when the light comes on and the blue dots (electrons) begin moving. Hence, remember to close the switch (if included) to make the circuit work. To edit your circuit, tap the circuit and delete or add some circuit elements. 12) A voltmeter is connected in select answer as series or parallel with the circuit. 13) An ammeter is connected in select answer as series or parallel with the circuit. D. Extend your understanding: 14) Which among the following connections is a (correct) series combination of cells? a) b) c) Multiple Choice: a or b or c? Answer is A …

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15) What is wrong with option c in #10? Write your answer below. 16) How do you call the cell combination in #10 b? 17) If you need to make 9.0 Volt battery by using 1.5 Volt cells, how many minimum cells you will need? And how will you connect them? In option C, the first two batteries make contact with the negative side. This is not the correct connection. Parallel connections You would require at least six cells. I would interface them by putting negative with the positive. Post-lab Questions: 1) Explain Ohm’s law, in your own words, but using the results of the lab activity. Ohms law states that the current flowing through an obstacle is proportional to the expected voltage. 2) What is the relationship between the slope of the Voltage vs. Current graph and the resistance of the wire in the circuit? The incline approaches the obstruction of the wire