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6. 2009 HSC Notes from the Marking Centre – Physics

# 2009 HSC Notes from the Marking Centre – Physics

## Introduction

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 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 Physics.

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 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 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’.

## Section I – Core

### Part B

#### Question 18

1. Better responses recognised the correct frames of reference. Weaker responses confused the values and units for distance and time.
2. Better responses linked the principle of relativity to inertial and non-inertial frames of reference.

#### Question 19

Better responses showed an understanding of electric fields and showed an ability to manipulate the equations for projectile motion. These responses recognised the direction of the force and the need to use the vertical component of the velocity. Some weaker responses confused force and acceleration and potential difference with velocity.

#### Question 21

1. Better responses determined direction of force on a current carrying wire in a magnetic field correctly.
2. Better responses identified data correctly and converted measurements to SI units. Some weaker responses incorrectly calculated the torque about end Y.
3. Weaker responses demonstrated some misunderstandings regarding torque and force. Common errors included incorrectly equating torque with force and assuming the magnetic field was constant in the equation τ = nBIAcosθ.

#### Question 22

Better responses named the replaced technology and gave reasons why it was replaced and described the application of transistors to communication devices.

#### Question 23

1. Better responses correctly identified the direction of the force between the wires.
2. Some weaker responses did not use SI units or stated that I² was the same as 2I.
3. Better responses described the forces acting on W2 and provided a net force.

#### Question 24

1. Better responses identified the correct band and provided a reason within the correct range. They used a ruler to determine the correct value from the graph.

#### Question 25

1. Better responses linked the magnitude of the charge to its sign.

#### Question 26

Better responses identified the two sources of energy loss and gave a description of how they are minimised, including the possibility of using new technology.

#### Question 27

1. Weaker responses were confused about the unit “nm”, leading to incorrect substitution.
2. Better responses demonstrated an awareness that the p-n junction set up an electric field, and linked this to the incident light and electron current.

## Section II – Options

### Question 28 — Geophysics

1. Better responses drew clear, well-labelled diagrams which showed a sound understanding of remote sensing.
1. and ii. Better responses substituted values into a given formula and took care when rearranging the formula.
2. Better responses commented on the possibility that a change in latitude or dense underlying rock could result in a similar value for the period.
1. Better responses remembered that P-waves arrive earlier than the larger amplitude S-waves. The time difference between these waves allows for the calculation of distance and hence the location of the epicentre.

### Question 29 — Medical Physics

1. Better responses linked the attenuation of x-ray photons to the contrast in the image.
2. Better responses drew a correctly labelled x-ray tube. They described how the electrons are produced and how the electrons’ energy is converted to x-rays.
1. Better responses identified that the increased acoustic impedance resulted in a greater percentage of ultrasound being reflected.
2. The best responses explained production of ultrasound waves from piezoelectric crystals in terms of electric potential and related the detection to this electric potential.
1. Better responses commented on the stated claim and linked this to the properties and uses of CAT scans.
2. Better responses linked the image to the positron emitting radioisotopes and a description of the two gamma rays produced.
1. Better responses exhibited sound knowledge of MRI. These responses were well structured and cohesive, they included the correct sequence of events and linked these to the production of the MRI image.

### Question 30 — Astrophysics

1. Weaker responses did not have a clear understanding of sensitivity.
2. Better responses clearly explained how interferometry and active optics can improve resolution and/or sensitivity, and included an explanation of why active optics is unsuitable for radio telescopes.
1. The better responses described a computer simulation of an eclipsing binary system and described the light curve as the graph of changing intensity against time as the stars pass in front of each other.
2. Better responses identified the correct formula and showed the substitution of values.
3. Better responses to this section stated specific differences between the spectra, explained these and linked them to the diagram in the question.
1. Better responses recognised that if B–V is positive the star is redder.
2. The better responses addressed a means of measuring the differing magnitudes.
1. Better responses used tables to compare photoelectric technologies with photographic methods.
2. Only the best responses directed attention to the key physical processes within a star as it evolves. These responses were cohesive and well structured. Weaker responses showed an inability to identify regions on the H-R diagram.

### Question 31 — From Quanta to Quarks

1. Better responses gave a full description of Rutherford’s model of the atom.
2. In better responses, candidates identified two problems with Rutherford’s model and linked Bohr’s model to these problems.
1. Better responses provided features of the de Broglie proposal.
2. Better responses identified the correct particle and linked the wave property observations to the de Broglie proposal. Weaker responses focused on a description of the experiment.
1. Better responses recognised mass defect as a nuclear process. These responses selected the most stable mass number and used the graph to compare stabilities.
2. In better responses, candidates were able to fully describe Chadwick’s experiment and correctly identify that he needed to apply the laws of conservation of momentum and energy to the collisions in order to determine the mass of the neutron.
3. Better responses communicated a thorough understanding of the standard model of matter, described theories and experiments that have added to our knowledge of the structure of the atom and identified some limitations of the standard model. These responses were cohesive and well structured.

### Question 32 — The Age of Silicon

1. & ii. In the better responses, candidates demonstrated the correct use of appropriate mathematics to determine the voltage.
2. Most responses correctly constructed a single truth table for three inputs, and correctly determined most of the relevant output states for the three possible interpretations of the non-standard circuits
1. Better responses correctly outlined the operation of a transducer.
2. In the better responses, candidates correctly outlined the correct use of a relay to safely control the pump.
1. Better responses outlined and contrasted digital and analogue information, some weaker responses confused controlled information with signal data information.
2. In the better responses, candidates linked a decreased power use within current ICs with the development and evolution of the IC and gave a relevant account of its energy reduction.
3. Better responses correctly gave relevant possible solutions and the best gave an appropriate overview of IC development and functioning to lead to their conclusion.

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