EXPERIMENT E1 Resistors and logic circuits 1.0 Introduction An electric circuit is a complete path from the positive terminal to the negative terminal of a power source. If the elements of the circuit are arranged in such a way that only one path exists for current flow (i.e. the current is identical for all elements), then the circuit is a series one. If an identical voltage exists across a number of alternative current paths then the circuit is a parallel one. Most practical circuits involve various combinations of series and parallel components. Of course components can be connected so that they are neither in series or parallel. Answer the following questions books: 1. If voltages are identical, then how are the components connected? 2. If currents are identical, then how are the components connected? 2.0 Series circuits 2.1 Series circuit theory your lab A typical series circuit is shown in Figure 2.1, this circuit having four resistors and a power source R1 R2 Vs R4 R3 Figure 2.1 The total resistance R, in the circuit may be calculated by a simple summation of the individual resistors: R=R₁+ R₂+R3+ R4 This may be extended for n number of resistors. From Ohm's Law, the total current in the circuit may be calculated. V, IR, or I, V₁/R₁ An important requirement of a series circuit is that the current is identical throughout the circuit. This feature will be observed in this experiment. 2.2 Requirements for series connection test Select the resistors 1k2, 82002 and 68092, and use the DMM set as an ohmmeter to measure their values. Record your results in Table 2.2, which is to be drawn in your lab book. 680-673 680 Rnom- x100 Rmea X100% Ruam Nominal Resistance Measured Resistance % Difference R₁ = 6802 673 1.03% R₂ = 820л 803-4♫ 2.02% R₁ = 1000 986 Series Rot=2500 J 2462 A 1.4% 1.5.4% Table 2.2 Connect the resistors in series on your breadboard, and measure the total resistance, Riot (do not connect the DC power supply yet, and do the % calculations outside lab time). 2.3 Voltage tests Draw Table 2.3 in your lab book. 15x 680г 2500 R₁ VR, = Vsx Rtot Quantity Measured value from Theoretical values using % Difference nominal values for V, and R DMM Vs 15.1 V Riot 2462.2 VRI 4-127 V VR2 4.9276 V VR3 6.047V IA 6.132X103 A 18 6-132X10 A Ic 6.132X10 A ID 6.192x-3A 13= 10-3 6.132 x 10 15V 2500 4-08 V 9-667% 1-504% 1-15% 4.92 v 0-154% 6 V 0-71% 0806A 2-15% 0-006A 2-15'1 4.0060 2-15% 0-006 A 2-15% Table 2.3 red V=15V R1-6800 D EQ DMM COM black B R2=82002 R3 = 1k0 Figure 2.3 Connect the variable DC power supply and, using the DMM in voltmeter mode, adjust the output to 15V. Measure and record the actual value from the DMM into Table 2.3. It is essential that this voltage remains unchanged at the recorded value for the entire series test. Figure 2.3 shows the meter connections for measuring the voltage across R₁. You will need to reconnect the red and black wires to measure the voltages across the other resistors. 2.4 Current tests The next part of the experiment is to measure the current at various points in the circuit. Use the DMM set up in ammeter mode to measure milliamps through the four points A, B, C and D. Note that it will be necessary to break your circuit and remake it in order to insert the ammeter. Record your results in the appropriate fields in Table 2.3 in your lab book. 2.5 Comments and conclusions Discuss the reasons for any differences in Table 2.2. Use Ohm's Law to calculate the current flowing in the circuit I, and hence calculate the voltage drop expected across each resistor (e.g. voltage drop across R₁ is calculated as VRI = IR₁, etc). Use the nominal values for the power supply voltage and resistances. Compare these theoretical values with the measured values and express them as percentage differences using the following formula: (Measured value - Theoretical value)/Theoretical value × 100 List the possible reasons for any differences. If any difference is greater than 5%, there could be a serious problem with either your calculations or tests, and checks will be needed. Comment on the sum of the three measured resistor voltages. Is this result consistent with expectations? Also comment on your current measurements. 3.0 Parallel circuits 3.1 Theory for parallel circuits DMM AMMETER mA COM RA Re red black Figure 3.1 A typical parallel circuit is shown in Figure 3.1. Parallel circuits have more than one path for current flow and there must be the identical voltage across all parallel paths. Two such paths exist in the example circuit as shown. The identical voltage appears across all the resistors in the circuit and the current through each arm is inversely proportional to the circuit resistance (from Ohm's Law). The total current in the circuit is given by I, la+Is (from Kirchoff's current law). Note the 'break-then-remake' method in order to measure the current using an ammeter. By Ohm's Law: L=V, RA I=V,/RB These can be substituted into Kirchoff's Current Law equation to give: I-V(1/R+1/RB) -V.((RA) + (RB)) =V(RARB)/[RA+ RB]) The term RRB / (R₁+ Rs) expresses the total value of resistance (R, V./I) in the circuit. In practice the inverse form, (R.)"' = (Ra) + (Ra)", is often simpler to work with as a calculator's inverse button (r) can be used thus reducing the amount of resistance data inputting. In addition this inverse form is directly extendable to any number of resistors. 3.2 Requirements for parallel tests The following table is to be drawn in your lab books. Quantity Measured DMM Value from Theoretical Values Calculated V₁ 10-03 v lov VRA 10-03 V OV VRS 10-03V lov VR6 NO-03V lo V =→/ 37-2 mA 0.0369 A Ib 14.9 MA I 12-5 CI 10-17 MA Riot 267.1 V=IR 0.0147 A 10 = Ix271 G-0122 A 0-01 A 10 = I 2717 271 Table 3,1: Parallel Circuit - 3 Resistors 680 1000 Select the resistors R4, Rs and R6 (k2, 82002 and 6802 respectively) as used in section 2.2. Use the DMM to measure their values and record your results. 3.3 Tests on three resistors in parallel b V₁-10V R₁ Rs Re 9 Figure 3.3 Connect the circuit as shown in Figure 3.3. Use the DMM to measure the total resistance, Riot and record it in Table 3.1. Then, using the DMM connected in the correct configuration, measure and record all the currents and voltages associated with this circuit, recording your results in your lab books in Table 3.1. 3.4 Comments and conclusions Comment on the relation between your measured V and I results and the voltage and current principles of the parallel connection./n 1. In the first part of the lab you will investigate the series circuits with resistors. a. Connect the resistors in series on your breadboard, and measure the total resistance Rtot (do not connect the DC power supply yet, and do the % calculations outside lab time). b. Voltage Tests: Connect the variable DC power supply and, using the DMM in voltmeter mode, adjust the output to 15V. Measure and record the actual value from the DMM into Table 2.3. It is essential that this voltage remains unchanged at the recorded value for the entire series test. Figure 2.3 shows the meter connections for measuring the voltage across R₁. You will need to reconnect the red and black wires to measure the voltages across the other resistors. c. Current Tests: the next part of the experiment is to measure the current at various points in the circuit. Use the DMM set up in ammeter mode to measure milliamps through the four points A, B, C, D. Note that it will be necessary to disconnect your circuit and remake it in order to insert the ammeter. Record your results in the appropriate fields in Table 2.3 in your lab book. 2. In the second part you will investigate the parallel circuits with resistors. a. Parallel circuits have more than one path for current flow, and there must be an identical voltage across all parallel paths. The identical voltage appears across all the resistors in the circuit, and the current through each resistor is inversely proportional to its resistance (from Ohm's Law). The total current in the circuit is given by I₁ = la + lɓ (from Kirchoff's current law). Note the 'break-then-remake' method in order to measure the current using an ammeter. b. Tests on 3 resistors in parallel: Connect the circuit. Use the DMM to measure the total resistance Rtot and record it in Table 3.1. Then, using the DMM connected in the correct configuration, measure and record all the currents and voltages associated with this circuit, recording your results in your lab books in Table 3.1. You should download the logbook Excel file from the VLE, and enter your measurements into the Excel file. You will use your logbook (and guidance from the Key Questions) to write a lab report. The lab report will be submitted on the FC312 Physics VLE page, via a Turnitin link in the Module and Assessment tile. Guidance: For this assessment you should make use of the following materials: • Resistors lesson notes Core textbook: AQA Physics A Level, Year 1 13.1-13.5 and Year 2 23.1 Please note: This is an individual assessment so you should not work with any other student. Your tutor will also ask for a draft copy of your report and provide written feedback. Before you submit this assessment, you will have an opportunity to receive feedback from your peers (other students in the class). Your tutor will arrange a time for you to share and discuss your progress with your classmates. You do not have to act on their feedback, but you may find it useful to enhance your final submission. Kaplan International Pathways 2 kaplanpathways.com Structure: Your lab report should contain the following sections: • • • ● • • • • Introduction. You should give a brief overview of the main theories behind the experiment. What is the background to this experiment? Aim. Clearly state the aim of the experiment - what are you trying to determine? Materials and methods. You should explain how the experiment was carried out. You should give enough detail so that another person can repeat the experiment in the same way you did. Results. You must include all your results. Results tables should be clearly labelled. All measurements must include units. If graphs are required, they should be an appropriate size and clearly labelled. Discussion. You need to explain what your results mean. You should link your results to relevant theories and explain how they fit together. You must use in-text citations where appropriate. Any unexpected results should be explained. Conclusion. State what has been learned from this experiment. Have you met the aim of the experiment? Errors. What may have affected your results? This section should include errors such as systematic, parallax and human errors ones that cannot be avoided. References. You should list all sources used. - Appendix. The raw data tables and the detailed calculations should be included here. Theory and/or task resources required for the assessment: You should refer to the appropriate chapters in the key texts as well as the lecture materials for the topic relevant to your experiment. Referencing style: You should refer to a minimum of 5 relevant sources for your report. You must include a Harvard style reference list at the end of your report. Expected word count: The lab report usually contains 1500-2000 words, excluding references. In each section you should include around the following number of words: • Introduction & Aim: 300-500 words Materials and methods: 300 words Results: 200 words Discussion: 500-600 words • Conclusion & Errors: 200 words Learning Outcomes Assessed: Apply good laboratory practice to the conduct of experiments, and to measure, record and interpret outcomes accurately using a lab report format Submission Requirements: You must include the following paragraph on your title page: I confirm that this assignment is my own work. Where I have referred to academic sources, I have provided in-text citations and included the sources in the final reference list. Kaplan International Pathways 3 kaplanpathways.com You must type your assessment in Arial font 11, with single spacing. You must submit the assessment electronically via the VLE module page. Please ensure you submit it via Turnitin. Assessments submitted after the submission deadline may incur penalties or may not be accepted. Addition submission information - check you have done the following: Formatting Consistent font, spacing, page numbers, formatting and subheadings Citations Correct format and location throughout the report Referencing Harvard referencing system used correctly in the reference list Summarising Paraphrasing Spell check Proof-reading Grammar Summarising the results of research Paraphrasing the contents of research findings Spell check the report Proof-reading completed Grammarly has been used to check the report How will this assessment be marked? Lab Report - (80% of assessment score) Experimental Procedure and Plan of experiment (10%) We will be looking for: • • • • • • Clearly defined aim of experiment Appropriate theoretical context Hypothesis with reasons List of equipment and consideration of safety procedures Clear explanation of method Clearly labelled diagram showing the equipment set-up Methodical practical skills (instructions followed correctly) Appropriate safety precautions Data Handling - Results (Tables, graphs, calculations) (15%) We will be looking for: • Good quality results with units • Recognition of outliers, repeat measurements to reduce uncertainty Equations, structural formulae • Correct mathematical manipulation in calculations, including units • Units on graph axes and/or table headings • Results quoted to correct precision, with consideration of errors Data Handling – Results (Uncertainty & Errors) (10%) We will be looking for: Identification of errors and discrepancies • Analysis of impact on results Kaplan International Pathways 4 kaplanpathways.com Discussion and Conclusion (30%) This will mainly be found in the Introduction, Discussion and Conclusion sections. We will be looking for: Clear explanation of the science underlying your observations Interpretation of results and graphs • Explanation of all results • • Confirmation (or otherwise) of hypothesis and/or aims Well-explained links to theory with equations Overall structure and quality of presentation (10%) We will be looking for: Attractive, clear layout with title page, headings, sub-headings • Neat, well laid-out tables with column headings • • • Neat graphs with titles, labelled axes and well-spaced, numbered scales Correctly formatted chemical and mathematical equations Calculations that are well laid out and easy to follow References correctly formatted and attributed • • Correct use of academic English: О Good English sentence structure Correct English spelling ○ ○ ○ 3rd person passive voice used correctly throughout lab report Paragraphs for each new section Academic integrity (5%) Information from sources is appropriately paraphrased/summarised rather than relying on quotes • Any direct and indirect quotations are clearly marked and acknowledged with correct citations • References match the citations and are correctly formatted • Data/facts presented are genuine and accurate Practical Skills - (20% of assessment score) Hazard identification video task - (10%) Health & Safety VLE quiz – (10%) The overall mark will be a percentage (0-100%). How will you get feedback? Your tutor will mark the assessment and provide you with a written feedback sheet. You can use this feedback to guide your further learning on the module. Kaplan International Pathways 5 kaplanpathways.com