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2010 HSC Notes from the Marking Centre — Physics



This document has been produced for the teachers and candidates of the Stage 6 course in Physics. It contains comments on candidate responses to the 2010 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 2010 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 Physics.

General Comments

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 their knowledge, understanding and skills developed through studying the course and including the prescribed focus areas. It is important to understand that the Preliminary course is assumed knowledge for the HSC course.

Candidates need to be aware that the marks allocated to the question and the answer space (where this is provided on the examination paper), are guides to the length of the required response. A longer response will not in itself lead to higher marks. Writing in excess of the space allocated 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’.

Teachers and candidates are reminded that mandatory skills content in Module 9.1 is examinable in both the Core and Option questions and that all objectives and outcomes, including the Prescribed Focus Areas, are integral to the Stage 6 Physics course.

In Section II, the Option question is divided into a number of parts. Candidates should clearly label each part of the question when writing in their answer booklets. Candidates are required to attempt only one question in Section II, and they are strongly advised to answer the option they have studied in class.

Section I – Core

Part B

Question 21

Although most candidates answered this question well, some candidates identified correct consequences but assigned them to the wrong angle. Other candidates identified correct consequences without explicitly relating them to angles A and C. In some cases, general consequences were outlined that could apply to both angles A and C (such as ‘heating’).

Question 22

  1. Although this question was well answered by most candidates, some incorrectly substituted the vertical height (instead of the horizontal distance) into the speed equation.
  2. A large number of candidates did not select the correct equation. When the correct equation was selected, common mistakes were: assigning zero to the vertical displacement; using the incorrect value for acceleration due to gravity; and not using an appropriate sign convention for vertical height or acceleration due to gravity.
  3. Despite the instruction to sketch the path on the diagram given, many candidates drew their own diagram. Where candidates did draw the path on the diagram given, a common mistake was to draw a path with the same range as shown in the diagram when in fact, if the acceleration due to gravity was higher, the range would have been shorter.

Question 23

  1. In better responses, candidates stated an acceleration of the train as the cause of the mass’s deflection and gave the direction of the acceleration.
  2. In better responses, candidates explained how both the horizontal and vertical components of motion contributed to the path drawn on the diagram and stated the frame of reference their analysis was taken from.

Question 24

In better responses, candidates explained the effect of increased gravitational attraction on the James Webb Space Telescope (JWST) from both Earth and the Sun, and then related this to the identical period of both bodies. Some candidates were not aware that the mass in Kepler’s Law of Periods equation refers to the central mass being orbited, not the orbiting masses.

Question 25

  1. In better responses, candidates included equations identifying the momentum of both the rocket and the exhaust gases, when describing the rocket’s motion. They were specific in their language with respect to the relative direction and magnitude of the momenta of the rocket and exhaust gases. Candidates are reminded that the law of conservation of momentum refers to the system as a whole, rather than individual components within the system.
  2. Many candidates correctly identified the relationship between thrust, mass and acceleration.

Question 26

  1. In better responses, candidates recognised that the magnet would have a greater velocity at Y. As a consequence, the rate of change of magnetic flux would also be greater and hence this would induce a larger potential difference at Y than at X.

    In weaker responses, candidates recognised that the magnet had a greater velocity at Y, but did not clearly relate this to the rate of change of magnetic flux. A common error was to relate an increase in velocity to an increase in flux change, rather than to an increase in the rate of flux change.

  2. Most candidates recognised that the polarity of the potential difference would be reversed when the magnet was dropped, with the south pole of the magnet initially entering the coil. In the best responses, candidates recognised that the total time taken for the changes in potential difference would decrease and clearly indicated this on their graph. They also included a clear indication of an increase in the magnitude of the potential difference at both X and Y.

Question 27

Most candidates named two applications of superconductors. In better responses, candidates provided a clear judgement of the impact of these technologies on both society and the environment.

In some responses, candidates provided impacts of the technologies on either society or the environment.

In weaker responses, candidates did not provide a judgement. A small number of candidates confused superconductors with semiconductors.

Question 28

Most candidates correctly indicated the strength and direction of the magnetic field. Some candidates stated the direction of the magnetic field correctly, but not the strength. A common error was failing to convert the increase in the reading on the balance to newtons. Some candidates also demonstrated poor algebraic manipulation skills.

Question 29

Few candidates understood that the graph shown in the display represents voltage as a function of time. A common error was the belief expressed that a cathode ray oscilloscope (CRO) uses magnetic fields rather than electric (or a combination of both). Some candidates used a diagram to complement their explanation.

Question 30

  1. Better responses identified the semiconductor as p-type, noting the number of outer electrons in boron and germanium in their justification.
  2. In the better responses, candidates clearly explained how the addition of boron alters the electrical conductivity, relating this to the greater number of charge carriers. In weaker responses, candidates provided some information about the conductivity of germanium without any explanation.

Question 31

  1. In better responses, candidates clearly linked the two formulae and accurately substituted values. Many candidates correctly identified the two formulae required, but could not convert nanometres to metres. Candidates are encouraged to write the formula in their responses before substituting values.
  2. Although many candidates correctly identified the photoelectric effect, most found it difficult to demonstrate a good understanding of the actual process. In better responses, candidates used correct terminology and explained the underlying physics succinctly.

Question 32

Many candidates did not demonstrate an understanding of gravitational potential energy and were unable to analyse the two problems related to a manned spaceflight to Mars. In relation to the problem of protecting the space vehicle from high-speed electrically charged particles, many students referred to protecting the astronauts from radiation by shielding, and were awarded marks for conveying this idea.

Section II – Options

Question 33 – Geophysics

Candidates who studied this option demonstrated knowledge of geophysics, relating their knowledge to both practical and theoretical questions, and using appropriate and relevant terminology. It was evident, however, that many candidates who attempted this question had not studied the option and, consequently, there were many non-attempts.

    1. Most candidates correctly identified three properties of earth materials.
    2. In better responses, candidates knew the shape of Earth and justified this with evidence based on the period of the pendulum.
    3. Some candidates had difficulty in changing the subject of the given formula to find the ratio of g1 and g2.
  1. In better responses, candidates presented a coherent and concise explanation. In weaker responses, candidates demonstrated a limited understanding of the basic concepts involved.
  2. Most candidates demonstrated a good understanding of seismic waves, describing the properties of S and P waves, identifying the relationships in the given equations and recognising the incorrect path of both waves.
  3. In better responses, candidates demonstrated a good understanding of plate tectonic theory and supplied evidence for its acceptance.

Question 34 – Medical Physics

  1. Some candidates gave a general description of how x-rays are produced, rather than showing how x-rays are used to produce an image.
    1. In weaker responses, candidates included general comments about isotopes without addressing an advantage and disadvantage of using an isotope with a six-hour half-life.
    1. Better responses included the three steps in the process. Most candidates demonstrated some knowledge of RF coils transmitting energy.
    1. In questions such as this one that require calculations, candidates are reminded to show all working, including writing the correct formula.
    2. In better responses, candidates included a definition of the Doppler effect and then related Doppler ultrasound to detecting a specific heart defect (eg malfunctioning heart valves, hole in septum). They explained how Doppler ultrasound measures change in frequency of reflected pulse to incident pulse, ie an increasing frequency indicates blood is moving towards the transducer, and decrease in frequency indicates the blood flowing away from the transducer, and the greater the magnitude of the change in frequency, the greater the velocity of the blood flow.

      In weaker responses, candidates were confused about the use of colour in Doppler ultrasound, many comparing it to red shift of star spectral lines.

  2. In better responses, candidates identified the most appropriate technique, gave a valid reason and validly discounted the other techniques – all while using their knowledge of the techniques and the images they form. They recognised that a small brain tumour will have a high metabolic activity which would allow it to show up on a PET scan.

    Some candidates wrote only about PET and CAT scans, not talking about ultrasound at all. In weaker responses, candidates described the technologies but did not make a judgement about which would be the most appropriate.

Question 35 — Astrophysics

    1. Most candidates did not recognise that the question referred to interferometry, given the huge baseline afforded by the satellite working in conjunction with ground-based devices, hence providing vastly improved resolution. Most candidates confined themselves to the advantage of having the telescope above the atmospheric interference.
    2. Most candidates identified atmospheric effects, and many gave a second advantage as the far lower temperatures of the stratosphere.
    1. Most candidates answered this question well, but it was concerning that some candidates demonstrated misunderstandings such as ‘emission’ spectra from normal stars, and ‘elements’ are given off by stars.
    1. Most candidates correctly identified stars in region Z as white dwarfs.
    2. Better responses linked the increase in mass to a decrease in time spent on the main sequence.
    3. Better responses stated that for stars in region W, fusion of hydrogen into helium (predominantly through the CNO cycle) was occurring, and that for stars in region Z there is no fusion taking place.
  1. In better responses, candidates identified three advances in measurement technologies and clearly described the improvement in understanding that each of them produced. They indicated what the understanding was before and after the advance in measurement technology, and so clearly described an improvement in understanding.

    In weaker responses, candidates wrote more than was needed, often including more than three advances. They often contradicted previous statements or wrote incorrect physics.

Question 36 — From Quanta to Quarks

  1. In better responses, candidates related the emission or absorption of energy and energy levels to Planck’s equation.
  2. In better responses, candidates substituted correctly into the appropriate equation.
  3. In better responses, candidates used standing waves and the whole number of waves per orbit to explain the stability of orbits.
  4. In better responses, candidates noted that Pauli hypothesised that the neutrino carries away some of the energy released in this nuclear reaction.
    1. Although most candidates described what Chadwick’s experiment included, some used the incorrect radiation particles to bombard beryllium. Conservation laws were poorly applied in some responses. Some candidates did not name a law, energy/mass/momentum in their answer.
    2. Although many candidates identified the neutral property of neutrons, they did not outline how this made neutrons useful in scattering experiments.
  5. Most candidates identified three forces that make stable isotopes – strong nuclear force, electrostatic repulsion and gravity. In better responses, candidates highlighted that strong nuclear force has the greatest effect on stability.
  6. In better responses, candidates described the work of the three scientists named. Weaker responses demonstrated only a basic knowledge by only referring to one or two of the scientists.

Question 37 — The Age of Silicon

    1. Most candidates correctly identified the thermistor and resistor as forming a voltage divider.
    2. In better responses, candidates calculated the voltage VT with respect to earth potential.
    3. Most candidates identified an op-amp connected with a form of feedback, but only in the better responses did candidates identify that the circuit used the open loop gain to act as a comparator or switch.
  1. Most candidates were conversant with the utility and application of relays which allowed them to describe and explain the operation of different relay types. Only the better responses linked the purpose of the insulator to the independence of the circuits.
  2. The better responses showed and correctly determined all possible eight outputs for the three inputs in a single truth table.
  3. Most candidates identified links between IC development, applications and societal usage. In better responses, candidates used diverse examples in their answer. Some candidates noted that the limitations of the recent development have been reached.


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