TMA 03 S217 Physics: from classical to quantum

Faculty of Science, Technology, Engineering and Mathematics S217 Physics: from classical to quantum

In answering these questions, take care to show your working throughout, and always indicate any principles or definitions you are using.

Take care to express all final answers to an appropriate number of significant figures, but also ensure that any intermediate values, or answers carried forward to another part, have sufficient significant figures to avoid propagation of rounding errors.

Please do not repeat the question text from this document in your eTMA submission as this is likely to be registered as possible plagiarism by our automatic detection system, and may lead to delays in returning your assignment.

We recommend that you look over Section 3 of the S217 Introduction and Guide before starting work on this assignment.

PLAGIARISM WARNING – the use of assessment help services and websites

The work that you submit for any assessment/examination on any module should be your own. Submitting work produced by or with another person, or a web service or an automated system, as if it is your own is cheating. It is strictly forbidden by the University.

You should not:

• provide any assessment question to a website, online service, social media platform or any individual or organisation, as this is an infringement of copyright
• request answers or solutions to an assessment question on any website, via an online service or social media platform, or from any individual or organisation
• use an automated system (other than one prescribed by the module) to obtain answers or solutions to an assessment question and submit the output as your own work
• discuss examination questions with any other person, including your tutor.

The University actively monitors websites, online services and social media platforms for answers and solutions to assessment questions, and for assessment questions posted by students. Work submitted by students for assessment is also monitored for plagiarism.

A student who is found to have posted a question or answer to a website, online service or social media platform and/or to have used any resulting, or otherwise obtained, output as if it is their own work has committed a disciplinary offence under our Code of Practice for Student Discipline. This means the academic reputation and integrity of the University has been undermined.

The Open University’s Academic Conduct Policy defines plagiarism in part as:

• using text obtained from assignment writing sites, organisations or private individuals
• obtaining work from other sources and submitting it as your own.

If it is found that you have used the services of a website, online service or social media platform, or that you have otherwise obtained the work you submit from another person, this is considered serious academic misconduct and you will be referred to the Central Disciplinary Committee for investigation.

TMA 03

Cut-off date 16 January 2025

This TMA is designed to test your achievement of the following learning outcomes for this module:

Knowledge and Understanding: KU2 Cognitive Skills: CS1–CS6

Key Skills: KS1, KS2

Practical and/or Professional Skills: PPS1, PPS2

This TMA contributes 5% towards your overall score for S217.

Question 1 - 20 marks

This question is designed to assess your reflection on your learning, your communication skills and your engagement with interactive Quiz 3, covering Units 7, 8 and 9. It also assesses your understanding of domestic electric power (Unit 10) and your application of physical principles in relevant situations.

(a) To demonstrate your engagement with Quiz 3, paste into your TMA answers a screenshot of either the summary page showing your performance on Quiz 3 or the screen that gives your overall score for this quiz. It does not matter what score you obtained, we are interested in your engagement with the quiz. Remember also that you may attempt the quiz questions as often as you wish, and each question has multiple variants that will be presented to you in turn, each time you try it. [2]

(b) In a few sentences, describe one thing that you learned from answering the questions in Quiz 3 that improved your understanding of gravitational or electric forces, fields or potentials. Your answer should be clearly explained and you should not need to write more than 100 words to answer part (b). [4]

(Even if you scored full marks on the quiz the first time you tried it, hopefully you learnt something of relevance in completing it. If you feel that this was not the case, your statement to this effect should be supported by your screenshot in part (a).)

(c) (i) In Unit 10 Section 5.2 Activity 3, you completed Table 10.2, reviewing your own use of domestic energy. Before attempting this activity, which of your electrical household devices would you have expected to use the most energy per day? Now you have completed the activity, was your initial assessment correct? Will you alter your use of your electrical household devices as a result of this calculation? Clearly explain your answer in one or two sentences. [5]

(ii) Assume that each of the electric lights in your home is a light emitting diode with a power rating of 11 W and is switched on for an average over the year of 2 hours per day, and that before the introduction of energy efficient lighting, all the light bulbs were rated at 60 W (and switched on for the same length of time). How many joules of energy has the change in lighting method saved per year?

(d) As explained in Developing your transferable skills and competencies, during your study of S217 you are likely to be developing important employability skills, many of which are also UNESCO’s key sustainability competencies. In Question 1 of each S217 TMA, you have the opportunity to reflect on your skills development.

(i) To what extent has reflecting on your skills development been useful so far in your study of S217?

(ii) How do you feel that reflecting on your skills development will be useful in the rest of your study of S217 and beyond?

Your answers should be clearly explained and you should not need to write more than about 50 words to answer part (d). [4]

Question 2 – 18 marks

This question is designed to test your understanding of gravitational forces and fields (Unit 8).

Consider two point-like objects M₁ and M₂, with M₁ having four times the mass of M₂. They are placed a distance d apart from each other.

(a) Sketch (in 2-dimensions) the gravitational field lines that are present in the region of space around the two masses. Show the direction of the field on the field lines. [8]

(b) Explain quantitatively where you should place a test particle such that it experiences a net gravitational force of zero from the two point-like objects. Indicate this position on your diagram. [10]

Question 3 24 marks

This question is designed to test your understanding of electric potential and potential energy (Unit 9).

(a) Two point charges with q₁ = +3.5 × 10⁻⁷ C and q₂ = −4.5 × 10⁻⁷ C are initially separated by a distance of r = 2.8 × 10⁻⁴ m.

(i) How much energy is required to double their separation?

(ii) What is the electric potential at the point midway between the two charges when their separation is 2r? [14]

(b) A uniform electric field of magnitude 1.0 × 10² N C⁻¹ exists between two parallel conducting plates, one of which is positively charged and the other of which is negatively charged. The plates are 1.0 × 10⁻² m apart.

(i) Calculate the magnitude of the potential difference between the plates.

(ii) If a proton is moved from the positive plate to the negative plate, what is the magnitude of the change in its electrostatic potential energy?

(iii) If this device operates as a capacitor, how is it able to store electrostatic potential energy? [10

Question 4  20 marks

This question is designed to test your understanding of electrical circuits (Unit 10).

(a) The circuit shown in Figure 1 can be used to measure the resistance of a platinum resistance thermometer (PRT). AB is a uniform resistance wire of length 1.00 m and C is a sliding contact on this wire. A standard resistor R is included in the circuit. The position of C is adjusted until the voltmeter V reads zero.

Figure 1 For use in question 4.

(i) By applying Kirchhoff’s laws to loops ADCA and BCDB, deduce an expression for the resistance of the PRT in terms of l₁, l and the value of the standard resistor. [5]

(ii) The PRT consists of 9.00 m of wire of diameter 8.4 × 10⁻⁵ m. The voltmeter reads 0 V when l₁ = 0.702 m and the standard resistor, R, has a resistance of 68 Ω. Use these values to calculate a value for the resistivity of platinum at the temperature of operation. Show that you have checked that the value for the resistivity and its unit are sensible. [12]

(b) Indicate briefly what factors might affect the precision of the measurement when using such a simple circuit to measure the resistance of the PRT. [3]