-SQA- SCOTTISH QUALIFICATIONS AUTHORITY HIGHER NATIONAL UNIT SPECIFICATION GENERAL INFORMATION

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1 -SQA- SCOTTISH QUALIFICATIONS AUTHORITY HIGHER NATIONAL UNIT SPECIFICATION GENERAL INFORMATION -Unit Number Superclass- -Title- RC ELECTRICAL AND MAGNETIC FIELDS DESCRIPTION- GENERAL COMPETENCE FOR UNIT: Solving problems associated with electrostatic and magnetic systems. OUTCOMES 1. solve problems involving electrostatic systems; 2. solve problems involving magnetic systems; 3. evaluate losses in magnetic materials. CREDIT VALUE: 1 HN Credit ACCESS STATEMENT: Access to this unit is at the discretion of the centre. However, it would be beneficial if the candidate had competence in basic electrical theory and practice. This may be evidenced by possession of NC module: Electrical Fundamentals Electromagnetics Electrostatics or similar qualifications or experience For further information contact: Committee and Administration Unit, SQA, Hanover House, 24 Douglas Street, Glasgow G2 7NQ. Additional copies of this unit may be purchased from SQA (Sales and Despatch section). At the time of publication, the cost is 1.50 (minimum order 5.00).

2 HIGHER NATIONAL UNIT SPECIFICATION STATEMENT OF STANDARDS UNIT NUMBER: UNIT TITLE: ELECTRICAL AND MAGNETIC FIELDS Acceptable performance in this unit will be the satisfactory achievement of the standards set out in this part of the specification. All sections of the statement of standards are mandatory and cannot be altered without reference to SQA. OUTCOME 1. SOLVE PROBLEMS INVOLVING ELECTROSTATIC SYSTEMS PERFORMANCE CRITERIA (a) (b) (c) (d) (e) (f) Explanation of the concept of an electrical field is clear and concise. Explanation of terms commonly used in electrical field theory are correct. Sketches of the field pattern associated with different types of capacitor are correct. Description of the construction of various types of fixed capacitor are correct. Calculation of total capacitance and electrical field strength of each dielectric of a parallel plate capacitor with two dielectrics is correct. Calculation of various electrical quantities associated with a series-parallel network of capacitors is correct. RANGE STATEMENT Terms: charge; electric flux; flux density; electrical field strength; absolute permittivity; relative permittivity. Different types of capacitor: parallel plate; concentric. Fixed Capacitor: paper; electrolytic; mica; polyester ceramic; tantalum. Various Electrical Quantities: total capacitance; total charge; charge on capacitors; voltage on capacitors; energy associated with capacitors. EVIDENCE REQUIREMENTS 2

3 Graphical and written and/or oral evidence of the ability to explain electrostatics field concepts, terms, components and sketch field patterns, and perform calculations on capacitive systems. OUTCOME 2. SOLVE PROBLEMS INVOLVING MAGNETIC SYSTEMS PERFORMANCE CRITERIA (a) (b) (c) (d) (e) Explanation of the concepts of a magnetic field is clear and concise. Explanation of terms commonly used in magnetic field theory are correct. Explanation of the concept of self and mutual inductance is correct in terms of the magnetic field patterns associated with an energised magnetic circuit. Calculations involving self and mutual inductance are performed correctly. Calculation of the magneto-motive-force in the coil of a three part composite ring magnetic circuit with a single air-gap and a coil wound round one of the composite parts is correct in terms of a given flux density in the air-gap. RANGE STATEMENT Terms: poles; magnetic flux; flux density; magnetic field strength; absolute permeability; relative permeability. EVIDENCE REQUIREMENTS Graphical and written and/or oral evidence of the ability to explain magnetic field concepts and terms, and perform calculations involving magnetic field quantities. Written evidence is required to show that the candidate can calculate 2 examples involving self inductance and 2 examples involving mutual inductance as detailed in PC(d). OUTCOME 3. EVALUATE LOSSES IN MAGNETIC MATERIALS PERFORMANCE CRITERIA (a) (b) Explanation of hysteresis losses in magnetic materials is clear and concise. Explanation of eddy current losses in magnetic materials is clear and concise. 3

4 (c) (d) Description of methods of minimising hysteresis and eddy current losses in magnetic circuits is clear and concise. Calculations on hysteresis and eddy current losses in magnetic materials are accurately performed. RANGE STATEMENT Minimising methods: composition of materials; heat treatment; mechanical handling; reduction in frequency; lamination. EVIDENCE REQUIREMENTS Written and/or graphical and/or oral evidence of the ability to explain different losses in magnetic materials and describe methods of minimising these losses and perform calculations to determine the losses as detailed in performance criteria (a)-(c). Written evidence is required to show the candidate can calculate one example involving hysteresis losses and one example involving eddy current losses as detailed in performance criterion (d). MERIT To gain a pass in this unit, a candidate must meet the standards set out in the outcomes, performance criteria, range statements and evidence requirements. To achieve a merit in this unit, a candidate must demonstrate a superior or more sophisticated level of performance. This may be demonstrated by: (i) (ii) explaining field concepts and terms (eg, a greater depth of knowledge or more penetrating grasp of concepts); transferring knowledge and skills to more complex field situations ASSESSMENT In order to achieve this unit, candidates are required to present sufficient evidence that they have met all the performance criteria for each outcome within the range specified. Details of these requirements are given for each outcome. The assessment instruments used should follow the general guidance offered by the SQA assessment model and an integrative approach to assessment is encouraged. (See references at the end of support notes). Accurate records should be made of the assessment instruments used showing how evidence is generated for each outcome and giving marking schemes and/or checklists, etc. Records of candidates achievements should be kept. These records will be available for external verification. 4

5 SPECIAL NEEDS Proposals to modify outcomes, range statements or agreed assessment arrangements should be discussed in the first place with the external verifier. Copyright SQA 1997 Please note that this publication may be reproduced in whole or in part for educational purposes provided that: (i) (ii) no profit is derived from the reproduction; if reproduced in part, the source is acknowledged. 5

6 HIGHER NATIONAL UNIT SPECIFICATION SUPPORT NOTES UNIT NUMBER: UNIT TITLE: ELECTRIC AND MAGNETIC FIELDS SUPPORT NOTES: This part of the unit specification is offered as guidance. None of the sections of the support notes is mandatory. NOTIONAL DESIGN LENGTH: SQA allocates a notional design length to a unit on the basis of time estimated for achievement of the stated standards by a candidate whose starting point is as described in the access statement. The notional design length for this unit is 40 hours. The use of notional design length for programme design and timetabling is advisory only. PURPOSE This unit will allow candidates to develop a knowledge and understanding of electric and magnetic field concepts and terms and to apply these field concepts to the calculation of important quantities in electric and magnetic field systems. The candidate will also be able to explain losses in magnetic materials and describe methods of minimising these losses. This unit would be suitable as a component of a Higher National course of study. CONTENT/CONTEXT The following information gives further clarification regarding the context in which outcomes and performance criteria could be achieved. Outcome 1 It is recommended that for performance criteria (a) to (c) the emphasis should be on the candidate obtaining a clear understanding of electric fields and terms used in electric field theory rather than an in-depth mathematical treatment of the subject. Field plots should be used to illustrate a number of typical field patterns (particularly the direction of flux lines and the position of equi-potential lines). Fringing effects associated with the two capacitor configurations in performance criterion (c) could be illustrated. Practical examples from both electronics and heavy current electrical engineering should be used to illustrate the beneficial and adverse effects of electric fields and capacitance. For example, in the case of electric fields such examples as lighting strikes and spark emissions in hazardous environments may be considered. In the case of capacitance such examples as smoothing in rectifier circuits, by-pass capacitors, stray capacitance associated with printed circuit boards and capacitive effects in high voltage cables may be taken. 6

7 Outcome 2 As in outcome 1 the teaching/learning strategy should emphasise fundamental magnetic field concepts and the meaning of magnetic field terms rather than the application of a heavy mathematical treatment. Field plots of typical magnetic field configurations should be used to illustrate such points as the direction of magnetic flux lines. Both permanent magnetic and electro-magnetic fields should be considered. Once again practical examples of magnetic fields should be used to illustrate both the beneficial and adverse effects of magnetic fields and inductance. For example the action of magnetic fields in motors/generators, in electromagnetic relays, in car ignition systems and stray magnetic field effects associated with cables could be considered. In the case of inductance, the effects of a choke in smoothing and lighting circuits and stray inductive effects in printed circuit board technology and cables could be taken. With reference to performance criterion (c) the application of both Lenz s and Faraday s laws should be included in both teaching/learning strategies and assessment. With regard to performance criterion (d) a double core transformer may be used as an example of an energised magnetic circuit. Both stray inductive effects associated with self and mutual inductance should be illustrated. It would be a useful exercise to compare typical electric and magnetic field patterns and the terms used in electric and magnetic field theory. Such a comparison should help to enhance the candidate s understanding of field concepts. APPROACHES TO GENERATING EVIDENCE During the work of the unit candidates should have a number of opportunities to develop problem solving and communication skills. Each candidate should be assessed at appropriate points throughout the unit. Where a candidate is unsuccessful in achieving an outcome, provision should be made for remediation followed by re-assessment. ASSESSMENT PROCEDURES In order to achieve this unit, it is suggested that the candidate attempts sequentially, at appropriate times, three summative assessments in a formal context and must present sufficient evidence that they have met all performance criteria for each outcome, as specified within the criteria for each outcome. Examples of Instruments of Assessment which could be used are as follows but should not be taken as mandatory. Outcome 1 A combination of restricted response and structured questions. Restricted response questions to measure performance criteria (a) to (d) and structured questions to measure performance criteria (e) and (f). For performance criterion (f) it is recommended that the series parallel network should have a minimum of five capacitors. 7

8 Outcome 2 A combination of restricted response and structured questions. Restricted response questions to measure performance criteria (a) and (b) and structured questions to measure performance criteria (c) to (e). Outcome 3 Use could be made of a multi-part extended response question. PROGRESSION It is recommended that this unit be offered in the early stages of the following HND awards: HND Engineering: - Electronics, Electrical, Telecommunications, Electronic Manufacture and Computer Technology. REFERENCES 1. Guide to unit writing. 2. For a fuller discussion on assessment issues, please refer to SQA s Guide to Assessment. 3. Information for centres on SQA s operating procedures is contained in SQA s Guide to Procedures. 4. For details of other SQA publications, please consult SQA s publications list. Copyright SQA 1997 Please note that this publication may be reproduced in whole or in part for educational purposes provided that: (i) (ii) no profit is derived from the reproduction; if reproduced in part, the source is acknowledged. 8