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There are resources on the Moodle page which will help you write your report: a specimen report; Word and LaTex templates. Plus, there will be lectures and demonstrations. Please check these resources and this document for the information you require but we are always willing to answer questions by email or when you are in the lab. Practicalities You will write 3 formal reports during this module: • One formal report on the Crater Experiment carried out in the lab. You will gain experience of formatting correctly your reports, using the templates, typesetting equations, producing graphs etc. You will write the abstract, introduction, methods, results, discussion and conclusions etc. This report is formative (I.e. it is assessed and feedback/mark is given. It counts toward your engagement with the module). One formal report on the Diode Experiment. This report is formative (l.e. it is assessed and feedback/mark is given. It counts toward your engagement with the module). You will refine your report writing skills and put right any mistakes you have made in the first report. [this report is worth 5% of overall module mark One formal report on an experiment that you carry out during the module. This will be a free choice (not the Diodes Experiment or the Workshop exercises) of one of the main experiments [this report is worth 25% of overall module mark]. You will submit an electronic copy through Moodle (the Moodle deadline is always the end of a week, not your lab session day). The reports will then be marked by the staff demonstrators and handed back to you in time for you to write the next report. Please refer to your module timetable for report deadlines. Style of writing You should use good English grammar, punctuation and spelling. Try to avoid unnecessarily complicated words or sub-clause constructions. Remember that good scientific writing has to be unambiguous and clarity is the objective. Do not use colloquial language in the report such as 'plugging numbers into equations' or similar. You should use a passive voice and past tense for a report. 'The sensor voltages were measured' and not 'I will be measuring sensor voltages'. Do not write (particularly in the Method) instructions to the reader [no numbered or bullet points] - you are not writing a script. You should re-read each section of your report as you write it to check it flows logically. Use a spell checker (but note that the spell checker is not infallible and won't check for the use of a correctly spelled but wrongly used words). Re-read your report before submitting it. It is acceptable for someone else (not an expert in the field, so not a physics friend) to proof read your work, provided you follow the School policy on proofreading, which is available in your Undergraduate Handbook (now online). Formal report templates To encourage you to format your formal report correctly, you must write it using one of the templates provided on Moodle. Any formal report failing to comply with the template will be returned to be reformatted before being marked. The structure and formatting elements are already correct so that you can concentrate on writing. There are some further advisory comments embedded in these templates to guide you as well, but these are only basics and must not be used on their own. We advise you to use either Word or LaTex (a typesetting engine used extensively in scientific and other publishing). If you want to try LaTex for the first time then we recommend you try www.overleaf.com which provides you with a set of tools and on-line help which are easy to use. We are able to provide some LaTex resources for you to get you started but we are not providing training within this module. You may have seen some use of LaTex in your Computing module. We will endeavour to answer questions or find someone who can. How much detail should your write? A scientific formal report should be a complete, self-contained summary of how the experiment was carried out, the results obtained, and the interpretation and significance of the results in light of the estimated errors and limitations of the experimental methodology. Importantly, a report is not a neater version of your diary, so it should be a SUMMARY of what happened and it should not give the 'gory details' of all the problems you had along the way, the details of the individual data points you measured, or generic details of how to use equipment. In other words, we do not want you to reproduce an instruction manual, lab manual or diary. Instead it should distil the important methodological details, including tricks that may not be obvious, key findings, and conclusions. Sufficient information (experimental and theoretical details and results) should be included so that the reader could replicate your experiment if they wished. The report will generally need to present some of the information contained in the Experiment Sheet (or other resources), but in your own words. You should assume that the reader has the background physics knowledge of a first year undergraduate, but is unfamiliar with the specific experiment (and does not have access to the Experiment Sheet - hence you should not use the instructions as reference in your report). Clarity of presentation and expression should be the overall aim in a report. You should write what is required to meet that aim. The target number of words should be 1800 to do this adequately with 1600 and 2000 being the recommended limits. We will not penalise you for straying past these limits: you will be penalising yourself as either you will be losing marks for insufficient detail, or you are spending too long on the work. Dealing with errors and mistakes in your data and analysis Data must never be made up or altered. We are aware that this sometimes happens at school; it is not acceptable at university and amounts to scientific misconduct. We take scientific integrity very seriously at all levels in this School. Likewise, do not copy someone else's results, even if your experiment has gone wrong, this is plagiarism. However, don't worry... unexpected features in your data can provide an opportunity for an interesting and thoughtful discussion. First, you do not have to report all the mistakes you made in the lab if you were able to correct them. For instance, you do not have to mention that you had to start the experiment again when you realised you were using a multimeter incorrectly. However, once you have left the lab it is impossible to be certain what you did. So if, when you are writing a formal report, you realise that you probably made a mistake in collecting the data, you should simply explain this possibility and use the discussion to discuss how this will have affected your results. Demonstrating your understanding of the experiment and analysis is the important skill we are assessing. When you plotted your data in the lab you may have noticed 'outliers'. Again, you may have been told not to plot these at school, on the assumption that they were noisy points that would average out if you acquired more data. This is also unacceptable practice at university - all outliers must be plotted, even in formal reports. Outliers are often interesting since they can indicate where the theory is breaking down. Again, if there is a good reason to believe that a particular data point was not acquired correctly you must plot it in your formal report but can comment on this and consider the effect on the fit or results of missing out that point. Very occasionally, if something goes seriously wrong with your experiment, a demonstrator will give permission for you to use some existing example data. In that case you must report the source of your data (to avoid plagiarism). If when you are writing your report you find a mistake in the analysis in your lab diary, you must correct it for the report: you still have the original data and you are not changing that. Similarly, you must correct error analysis, or complete it if you did not have time. You must also use a more sophisticated method of analysis for your formal report (for instance you must use python, Excel or other suitable software to calculate the gradients (and uncertainty in gradient of your graphs). As you have to use a graphing process on a computer, this is what you will be doing anyway. Remember you are adding value to your experiment in a report - you have already been marked for getting the data. Structure Reports must always be conventionally structured, as laid out in the First Year Lab Report template (available on the First Year Lab Moodle page): Title Information: A meaningful title – which doesn't have to be the one from the original script, which describes simply what the report is about. You should have your name, the day and date you did the experiment. Abstract: The abstract should be about 150 words. The purpose of the Abstract is to inform the reader as succinctly as possible what the report (or paper) is about. The Abstract is a stand-alone document in- itself, to be read independently of the main report and should be a summary of main points. There is a reason for the format and content, which might seem a bit old-fashioned and odd at the top of your report. Journals, papers, and other published works are indexed by databases such as Web of Science or Google Scholar. With the citation information the abstract rather than the whole paper is searchable. A researcher can search and locate interesting papers and see which ones they want to read (or buy). We ask you to do this because as a researcher writing a paper, getting the abstract right is an important part of your work. We suggest thinking about the abstract in a similar way to the main report. This is not fixed formatting but write one or two sentences about each of the following themes: Context and Experiment Aims; The physics involved; Brief description of important parts of method (what specific measurements were made) so how aim was achieved; The key values and their uncertainties found; a simple conclusion commenting on main contribution to uncertainty. There should be no citations unless spelled out completely (really no need in this type of report) and all abbreviations should be defined as well as in main report text. There must not be any reference to figures or equations from the main text. It should contain the outcomes and key finding(s), e.g. a value and its uncertainty. The abstract is not an introduction or a list of aims. Think of it as a completely independent document from the main report (although contained within the report). Introduction: Should contain several key points which are: 1. Context and Background - You need to explain why we might want to do this experiment. You should identify the important physics underpinning the experiment and read up on this. There may be a historical perspective or even a current application you feel is relevant to the experiment that you wish to highlight. Putting your own background research findings (with citations) in the introduction will earn you more marks than simply repeating material from the experiment sheet. We would expect one or two diagrams/graphics to highlight an aspect of this background or context. 2. The theory underpinning this experiment - what we already know. You may describe the basis for and derive the key equations. Show, for example, diagrams of field lines or similar concepts where relevant. In your first year reports this section is not likely to be big enough to warrant a Theory section all on its own. In future years you may wish to do this depending on the type of project you are reporting. A diagram can be usefully employed to assist in explaining the theory, for example this could be to show the geometry of the theory described. 3. Aim(s) what you wanted to do. The hypothesis you are testing if applicable. Methods: Here you describe the important features of your experimental method. This should be a report on what was done, not an instruction sheet. Again, it is about adding value in the report over and above the information you were given. 1. Experimental details relevant to others who want to repeat the experiment. For example, it may be helpful to give the make and model number of an important piece of equipment but you do not need to give obvious details on how to operate it (for instance, you do not need to give the sort of information that is found in a user manual). This is where a good diagram (with connections and important dimensions) comes into its own. A photograph can be a useful 2. addition if the layout of apparatus is important, but a diagram is far more valuable. If we only put photographs in the Lab Manual rather than diagrams there would be complaints! Having said that we want you to draw your own diagrams so we have deliberately only given you the minimum number of diagrams to do the experiment. Hence there are photos in the instructions where specific features are being highlighted. Do not write as instructions, as lists of bullet points. Write what you did in past tense, passive voice. 3. How you analysed the data you collected. This is part of the method because it can sometimes - be integral to the working of the experiment – like software or fitting of data to functions. In the first year this is limited to linear fits and graphing, but this should be stated. There is no need to include formulae for mean, SD or SEM in methods, these are assumed knowledge. 4. An outline of how you analysed your errors. Avoid saying 'the results were analysed in python/matlab/excel' when you really mean that you performed an unweighted least-squares fit. Results: This section should contain words to link the results together, not just diagrams! Discussion of your own measurements and results should be carried out where the graphs are. The Discussion section has a separate function of its own. e.g. 'Figure 1 plots the relationship between A and B, and the gradient of this graph was found to be m. This was then used to calculate Z via Equation N'. Other points to be aware of: 1. If you made a mistake in analysis in the lab or diary you must rectify it in your report - but obviously you can't change your raw data! 2. You should never tabulate raw data in a report, but rather you should always plot a graph from which you derive a result. 3. Graphs should include a line of best fit or trend line, labelled axes, units and error bars (as required). Axes should be scaled appropriately and the graph formatted for clarity (markers, axes, lines and text should have good visibility). Graphs should never have a title above, but have a suitable caption below. Please see video and lecture material about graphing. 4. Experimental data should be plotted as un-joined points (use suitable markers) whereas fits to the data should be plotted as lines. It is worth repeating again how the fitting was achieved, either a weighted or an un-weighted least-squares fit. 5. All numerical results must be quoted with an estimate of their uncertainty and a unit, but you do not need to give the detailed calculation of the errors (we don't need to see explicit numerical calculations in the report, formulae for basic equations such as mean). We have already marked and commented on such detail in your diary anyway. You just need to indicate how you arrived at that uncertainty (e.g. 'R was found from the gradient of the graph shown in Figure 2, and the error in R was found using an unweighted least-squares fit.'; or ‘using the theory outlined in the introduction, and propagating the errors through Equation 4, the value of T was found to be ...'). No need to reproduce calculation details in a report./n Diodes Assumed knowledge and recommended study You will have covered the following topics at A level: • the current-voltage curve for a diode when used in forward bias; • the equation E = hf, where E is the energy of a photon, h is Planck's constant and f is the frequency of the photon; the electron volt as a unit of energy and how to convert between joules and electron volts; • • how to calculate wavelength from a given frequency using the wave equation; • • constructing circuits from circuit diagrams using a range of components, including those where polarity is important; how to measure current and voltage in a circuit using electrical multimeters; • using V = IR to calculate current through a resistor. It is recommended that you revise how to set-up a circuit on a breadboard (see the Lab Handbook and https://www.sciencebuddies.org/science-fair-projects/references/how-to-use-a-breadboard). Planning 1. Read this worksheet. Watch the video series on Semiconductors and Diodes. View the experiment equipment by watching the video named 'Diodes Experiment Equipment'. 2. Sketch the expected I-V curve for a diode in forward bias. 3. Sketch the expected I-V curve for a diode in reverse bias. 4. Research the ideal diode equation (also known as Shockley diode equation) and write down the simplified version for a diode in forward bias. Include a reference for where you obtained the information for this equation. State what all the letters/symbols in the equation represent. You do not need to show the derivation of the equation or explain what the letters/symbols in the equation mean. 5. In your Lab Diary write a brief plan of your experiment. Include: a statement of aims; a summary of the experimental procedure; equations needed for data analysis; expected results and sketch graphs with the expected trend line; suggested sources of expected uncertainty and appropriate error propagation equations. Experiment You are provided with: • A variable power supply unit (PSU) (0-30 V dc @ 3 A). To turn on: switch on and press the button marked OUTPUT. • Two digital multimeters. Do not connect the ammeter across the output of the power supply, as you will fuse it. • A piece of breadboard. ● Red wire to use for +V and black wire to use for -V. • A silicon diode. • 5 different coloured LEDs. • A 220 Q resistor, a 2200 resistor and a 1 M 2 resistor. The forward characteristic Set the circuit up as in Figure 1. Please check the following before switching on: • • • All knobs on the power supply are fully anticlockwise. If a yellow light shows on the power supply, turn up current slightly until it turns green. The milliammeter is set on the DCA 200 m range and terminals COM and mA are used. The voltmeter is set on the DCV 20 range and 220 Ω Figure 1 Experimental setup for measuring the forward characteristics of the semiconductor diode. I. terminals COM and V are used. The diode is connected correctly. Plot the current-voltage characteristic. Use currents of no more than 30 mA. Pay particular attention to the region around 0.6 V where the diode turns on (just use the fine voltage adjust knob). The reverse characteristic II. Rebuild the circuit as in Figure 2. The reverse current is very small and it is too small to be measured using the current setting on the multimeter. Therefore, use the voltage across the 1 M resistor to determine the current through the circuit. III. Plot the I-V curve for reverse voltages up to 12 V. 1 ΜΩ + Figure 2 Experimental setup for measuring the reverse characteristics of the semiconductor diode. LEDs (Light Emitting Diodes) IV. You are provided with a set of LEDs of different colours; the wavelength, 1, of the light produced by each LED is given. Build the circuit as in Figure 3 with one of the LEDs and a 2200 resistor in series with the LED (the 2200 Q resistor limits the current flow and protects the LED). Measure the voltage at which you can see light first being emitted, V₁, for each LED when it is forward biased. V. When an LED is forward biased and the applied voltage is raised to the depletion potential, electrons from the n-type material and holes from the p-type material flow into the active region of the LED. When an electron and a hole recombine in the active region a photon of frequency f is emitted. 2200 Ω + Figure 3 Experimental setup for measuring the turn-on voltage across an LED. The energies of the electrons and holes within a doped semiconductor can be affected by other processes, such as thermal effects, so it's possible that some electrons and holes might have enough energy to move into the active region of the LED before the depletion potential has been reached. This means that light will start to be emitted before this potential is reached, however, you will only see light being emitted when the intensity of the light is high enough for your eyes to detect. Assuming all the LEDs in this experiment have the same (or very similar) characteristics (or ideality factors), then the energy of the photons emitted can be given by, hf = eV₁ + C, [1] where e is the charge on the electron, h is Planck's constant, and C is a constant to account for the difference in energy caused by thermal and statistical processes. Plot a graph of V₁ against f. Use the gradient of your graph to estimate a value for Planck's constant.