2009 HSC Notes from the Marking Centre – Electrotechnology
This document has been produced for the teachers and candidates of the Stage 6 course in Electrotechnology. It contains comments on candidate responses to the 2009 Higher School Certificate examination, indicating the quality of the responses and highlighting their relative strengths and weaknesses.
This document should be read along with the relevant syllabus, the 2009 Higher School Certificate examination, the marking guidelines and other support documents which have been developed by the Board of Studies to assist in the teaching and learning of Electrotechnology.
Teachers and students are advised that, in December 2008, the Board of Studies approved changes to the examination specifications and assessment requirements for a number of courses. These changes will be implemented for the 2010 HSC cohort. Information on a course-by-course basis is available on the Board’s website.
Teachers and candidates should be aware that examiners may ask questions that address the syllabus outcomes in a manner that requires candidates to respond by integrating the knowledge, understanding and skills they developed through studying the course.
Candidates need to be aware that the mark allocated to the question and the answer space (where this is provided on the examination paper), are a guide to the length of the required response. A longer response will not in itself lead to higher marks. Writing far beyond the indicated space may reduce the time available for answering other questions.
Candidates need to be familiar with the Board’s Glossary of Key Words which contains some terms commonly used in examination questions. However, candidates should also be aware that not all questions will start with or contain one of the key words from the glossary. Questions such as ‘how?’, ‘why?’ or ‘to what extent?’ may be asked or verbs may be used which are not included in the glossary, such as ‘design’, ‘translate’ or ‘list’.
Candidates were required to recognise and name three components from circuit diagrams. Most candidates recognised the fuse (a) and the variable resistor or potentiometer (b), but the change in context to the symbol for double insulation in Part (c) was a challenge for most, with few correct responses.
- This question was answered well by most candidates, with V=IR being the most common formula submitted. Not all candidates provided a formula as required in the question. Some provided the symbolic representation of the relationship, but this did not adequately answer the question.
- Many candidates correctly applied Ohm’s law and determined that I=2.5A.
- Candidates had little difficulty translating the colours from the chart to the figures required. Poorer responses did not use the multiplier or the tolerance value and obtained the wrong answer.
- Many errors were made in reading the question, which asked for the maximum value of the resistor. Many candidates calculated the 5% tolerance of the 20MΩ resistor correctly as 1MΩ but did not add it to the 20MΩ value to give the correct maximum value of 21MΩ. This part of the question was not generally well answered.
- Most candidates were able to recognise the fuse and lamp in the circuit diagram. Some variations, such as ‘light globe’ or ‘light’ were equally rewarded. Responses such as ‘load’ were too general to meet the requirements of the question.
- Better responses described the flow of current in the circuit and the resulting lamp illumination. Poorer responses referred only to the light coming on, or listed the results of a closed switch rather than describing what occurs.
- This question was poorly answered by most candidates. Only the best responses identified the short circuit caused when Switch 2 was closed, with the result being that the fuse blows and the circuit goes ‘open’. Many candidates misunderstood the true nature of electricity and reported that the lamp would dim or the current would be shared down the paths provided by the closing of both Switches 1 and 2. These poorer responses gained no marks.
- Better quality responses recalled the formula for the time constant of a circuit, T=RC. They calculated the result and did not lose track of the decimal point. Poorer responses misplaced the factors of 10 and were left with 705 seconds or other incorrect variations.
- Most candidates applied the formula for Ohm’s law by correctly reading the values from the circuit diagram and accurately calculated the maximum circuit current (6.67mA).
- Better responses not only calculated the total resistance for the circuit using R=T/C but also recognised that there was an existing 15kΩ in the circuit and calculated the difference between the two resistances to give 6276Ω correctly. Poorer responses either missed this subtraction or did not transpose the time constant formula correctly.
- Variations in the name of a pop rivet gun were accepted as correct. Most candidates were able to identify an application for it. Poorer responses misnamed both the tool and consequently its application. Correct applications of the pop rivet gun were presented by some candidates without specifying its name.
- Good responses to this question correctly identified the combination pliers and identified many uses for them. Most candidates were able to respond regarding an application of twisting, holding or the cutting of wire in the electrotechnology context.
- Many candidates responded to this question as if it related to a small-scale generation. Better responses explained that the current flow is generated by a conductor moving through a magnetic field in a turbine. Some mentioned wind-powered turbines for operating a generator. Poorer responses did not give any correct explanation of how electrical current is generated.
- Most candidates correctly identified a renewable generation technology such as wind, geothermal, tidal or hydro. Poorer responses indicated that solar cells or oil provided renewable generation, which did not answer the question and could not be awarded marks.
Better responses to this question included the setting-up of the analogue ohmmeter by zero adjustment and range selection, going on to describe the checking of its operation against a known quantity. They referred to possible reading errors due to parallax or viewing at an angle. Some candidates made reference to only ‘not contaminating’ a correct reading with finger touch. Poorer responses generally referred to only one aspect of setting up the meter such as zero adjustment.
Better responses showed the working that was asked for and showed calculations of the series and parallel resistances, and arrived at the correct answer of 85.1Ω. Some candidates rounded this value down to 85Ω, which was considered a practical approach. Poorer responses misunderstood the circuit diagram, or did not apply the process for totalling parallel resistors or, in some cases, did not accurately sum the series resistance.
Better responses clearly described a safe and sequential approach to the isolation of the 230V motor. These responses wrote a clear and sequential list of procedures that allowed for the correct use of testing equipment, including the validation of its correct functioning and the use of appropriate PPE and on-site safety procedures such as signage and ‘danger’ or ‘lockout’ tags. These responses used technical language, applied standard processes with test equipment, and OHS practices. Some candidates mentioned the need for good communication when discussing customer/client contact in the context of OHS and safe use of equipment.
Too many responses discussed servicing the 230V motor, when this was not asked for.
Poorer responses did not show that they could apply their experiences in electrotechnology to this real-life situation. These responses were typically too brief, and lacked technical language and workplace knowledge.
Many candidates lacked fundamental understanding of tapping drill sizes and the use of a tap to remove material. Many candidates specified a 10mm diameter drill for an M10 tapped thread. Candidates need to be reminded that the tapping drill is always smaller than the tap. Technical terms and the names of tools needed for this task were often misnamed or used incorrectly.
Better responses clearly understood the process, including the use of punch, correct drill size, three taps, PPE, lubricant, and the safe and appropriate use of the tools involved. Some candidates included the justification of the use of some tools by comparing them to others, such as a bench drill to a portable drill.
The safe use of tools was handled well with some exceptions, including the misuse of some tools being used to achieve the task.
Better responses wrote extensively about the interaction between service personnel and the customer. However, many interpreted the question in a naive manner and felt that the irate customer was angry with them personally and that they had done something wrong, whereas the customer was unhappy about the loss of supply. Most could identify that they had to pacify the customer and manage the communication carefully throughout the resolution of the power loss.
Better responses indicated the need for an ongoing customer update concerning progress in rectifying the fault. These responses demonstrated some investigation of the fault by discussion with the customer and management, and appropriate systematic fault diagnosis. They correctly used appropriate and tested equipment. These candidates had correctly addressed both aspects of the question: the ‘customer service’ issue and the ‘loss of supply’ issue.