PHAS0008 - Experimental Methods Coursework (2024-25)
To be submitted via Moodle/Turnitin by 17:00 on Monday 24th February 2025.
Answers to questions 1 - 3 should be type-written and submitted as a single pdf file. Please be careful to explain your methods and working in your pdf file.
Supporting Python notebooks or spreadsheets for Q1c should be uploaded separately, but please note that your pdf file should contain your answers and explain fully your working for these questions.
All files submitted must be named in the following format:
• {student number}-{description}.{extension}
Useful information can be found on the PHAS0008 Moodle pages, for example under Module Resources and Documentation.
Please remember we expect our students to maintain the highest Academic Integrity during their studies - please read the guidance and note that you will be required to submit your UCL Academic Integrity course Certificate before you can submit your coursework.
Provisional part marks are shown in [brackets].
Q 1. a) Write down expressions for r2, x2 and reduced xr(2)ed, and explain the meaning of each symbol in these equations. [3]
b) Explain how r 2 and reduced xr(2)ed tests can be used to provide guidance on which of two or more theoretical models is the best fit to experimental data. Explain also, using sketches if necessary, the meaning of the term overfitting in the context of theoretical fits to experimental data. [5]
c) Students were tasked to use a current balance to investigate how the magnetic force, F, perpendicular to a linear conducting wire varies with the current I. To this end, the position, y, of a small counterweight was measured such that F Ⅸ y. Diagrams and the data collected are given in the supporting file PHAS0008-CW-data-images-2024-25-v1 and the Table below.
Table 1: Current balance data for y vs I
|
Current (I) / A
Runs 1,2,3 ΔI
|
Counterweight position (y) / mm
|
|
Run 1
|
Run 2
|
Run 3
|
Δ y
|
|
0.2 0.005
|
1.6
|
1.6
|
1.4
|
0.2
|
|
0.4 0.005
|
3.2
|
3.4
|
3.2
|
0.2
|
|
0.6 0.005
|
4.8
|
5.0
|
4.8
|
0.2
|
|
0.8 0.005
|
7.4
|
6.6
|
6.6
|
0.2
|
|
1 0.005
|
8.6
|
8.8
|
8.6
|
0.2
|
|
1.2 0.005
|
11.2
|
10.8
|
11.0
|
0.2
|
|
1.4 0.005
|
12.6
|
12.8
|
12.8
|
0.2
|
|
1.6 0.005
|
14.8
|
14.6
|
14.6
|
0.2
|
|
1.8 0.005
|
17.0
|
17.2
|
17.2
|
0.2
|
|
2 0.005
|
19.4
|
19.2
|
19.2
|
0.2
|
By minimizing x2, fit the data for y vs I to a series of polynomials of form.: a0, a0 + a1I, a0 + a1I + a2I2, and a0 + a1I + a2I2 + a3I3 . Plot the data and the fits. For each fit, please also give r 2, x2 and reduced xr(2)ed. Please note: you should fit to and plot one combined mean dataset (with appropriate uncertainties) rather than Runs 1, 2 and 3 separately. Please also remember to show all your working in your main pdf file. [10]
Hence, discuss which order polynomial provides the best fit to the data and, therefore, whether the results are consistent with a linear relationship between the magnetic force, F, and current, I. Comment also on whether the students have estimated their uncertainties correctly, and whether their experiment would benefit from another repeat with the same equipment. [6]
Q 2. a) Summarise the steps involved in conducting a risk assessment for an experiment. When should a risk assessment be conducted? [2]
b) Explain what PAT testing means, and, in this context, Class 1, Class 2 and Class 3 appliances. Sketch the symbols for Class 1, Class 2 and Class 3 appliances, and give 2 examples of each type of appliance. [4]
c) With regards to laser safety, explain what is meant by the acronyms AOR, AEL and MPE. Describe the basis for the following classifications of lasers: Class 1C, Class 2M and Class 4. [4]
d) To provide the Laboratories with liquid nitrogen, a 150 L cryogen storage dewar is filled on the loading bay outside the Department (entrance near the Massey lecture theatre), carried up in the lift and thence into the Lab. Write a risk assessment for this procedure. Please remember to be quantitative where possible, for example, when considering the volume of nitrogen and the lift. [6]
Q 3. a) In the context of referencing, explain what is meant by the acronym “ DOI” . Please give the DOI for the PHAS0008 “Experimental Guidance Notes” on experiment NX741. [2]
Choose two research articles published in the last 12 months that you find interesting in the broad field of physics, selected from the JournalsNature,Science,Nature Physics, Nature CommunicationsorPhysical Review letters. At least one of your choices should include a UCL author, for example from the UCL Department of Physics & Astronomy, to be highlighted in bold.
Please be careful to choose original research articles, rather than reviews/commentaries.
b) For your chosen articles, provide the full reference in IEEE format, including the title and DOI. [2]
c) Write a short (maximum 100 word) summary of each of your papers (so, 2 summaries in total) in your own words, including the context, experimental methods, main results and conclusions/significance. An example, from 2023, is provided below. [6]
[1] Albrechtsen, S.H., Schouder, C.A., Viñas Muñoz, A., Christensen, J.K., Petersen, C.E., Pi, M., & Stapelfeldt, H. Observing the primary steps of ion solvation in helium droplets. Nature 623, 319–323 (2023).https://doi.org/10.1038/s41586-023-06593-5
The interaction of ions with solvents is an important fundamental process, with relevance across a broad range of natural and applied sciences. This paper describes experiments in which sequential solvation of a sodium ion by helium atoms was probed over picosecond time-scales. The team first created liquid helium nanodroplets. By exploiting laser-induced ionisation of neutral atoms, they then implanted a single Na+ and, a short time later, Xe+ ion. Spectroscopic interrogation of the ejection of Na+ Hen clusters was then used to track the sodium-helium solvation in realtime. This work opens the door for new insight into time-resolved ion-solvent binding. [100 words]