Physics 2020 HSC exam pack

Students should:

• read the question carefully to ensure that they do not miss important components of the question
• have a clear understanding of key words in the question and recognise the intent of the question and its requirements
• plan the response to assist in the logical sequencing of information
• integrate relevant scientific terms into their responses
• show clear cause and effect relationships related to key physical concepts in explanations
• engage with any stimulus material provided and refer to it in their response when required by the question
• show full working in calculations including formulas and substitution into formulas
• include correct units and directions for vector quantities for calculated values
• review their response to ensure that it addresses the all the requirements of the question
• be familiar with the constants and formulas provided on the Data and Formula Sheets
• be familiar with the SI units of all relevant quantities and the relevant prefixes and their abbreviations
• be able to plot graphs and understand the relationship between the graph and the relevant concept
• be able to extract quantitative relationships from graphs
• be familiar with key physical principles such as, conservation laws and laws of motion and be able to apply them in a range of contexts
• be able to discuss how a range of models are applied in Physics and the evidence used to validate them.

Question 21

In better responses, students were able to:

• describe the behaviour of electrons in the Bohr model according to Bohr’s postulates
• relate the conservation of energy to the transformation of energy from an electron changing energy levels to the energy of the photon emitted or absorbed.

Areas for students to improve include:

• being able to recall specific features of Bohr’s model of the atom.

Question 22(a)

In better responses, students were able to:

• identify the correct equation and substitute in values appropriately
• record an answer correctly rounded and with correct units.

Areas for students to improve include:

• knowing the symbols for all quantities in the question
• choosing the correct equation.

Question 22(b)

In better responses, students were able to:

• link the slow movement of the capsule relative to the speed of light with the limited effect that will have on quantitative analysis
• identify that the capsule is a non-inertial reference frame, and therefore, that it is not appropriate to use special relativity to analyse its motion.

Areas for students to improve include:

• using specific language to address the question unambiguously
• ensuring that when TWO points are provided that they are clearly distinct from one another.

Question 23

In better responses, students were able to:

• extract the correct angular momentum value from the graph
• substitute the correct values into the equation provided to calculate the current
• state the effect of calculated current on the circuit breaker and hence the motor.

Areas for students to improve include:

• being explicit when identifying the resultant effects on the motor
• reading scales of graphs with precision.

Question 24

In better responses, students were able to:

• extract and use key data from the graph
• use appropriate equations to calculate aspects of projectile motion
• show correct process to find the resultant from a vector sum
• use trigonometry to find the angle of projection.

Areas for students to improve include:

• identifying precisely the of values from a graph
• distinguishing clearly between the initial and average velocity the projectile.

Question 25

In better responses, students were able to:

• correctly describe the quarks, leptons and bosons associated with the hydrogen atom.

Areas for students to improve include:

• applying the standard model of matter to the whole hydrogen atom
• correctly associating specific bosons with fundamental forces.

Question 26(a)

In better responses, students were able to:

• indicate the continuous nature of the incandescent light spectra and the discrete nature of the emission spectra produced by a gas discharge tube.

Areas for students to improve include:

• using clear language when describing an discontinuous emission spectrum
• distinguishing between an emission spectrum and an absorption spectrum.

Question 26(b)

In better responses, students were able to:

• provide the underlying continuous wave assumption for curve X and the particle quantum model of light assumption for curve Y.

Areas for students to improve include:

• being clear in linking between the models and the underlying assumptions behind the models.

Question 26(c)

In better responses, students were able to:

• sketch a curve wholly under the 5000k curve, with appropriate x intercepts or asymptotes, with an accurate lower peak value
• calculate the peak frequency for 4000 K
• provide clear links between temperature and both wavelength and intensity.

Areas for students to improve include:

• taking more care with curve sketching, improving accuracy and effective labelling
• having consistency between written and drawn explanations
• ensuring that they are answering the question as written, that is, by providing an assumption, not a consequence of the assumption.

Question 27

In better responses, students were able to:

• use mathematical expressions to explain the relationship between variables provided and identify the changes required to maintain constant fringe separation
• identify the relationship between sin ϴ, distance to screen(y) and fringe separation(AB)
• substitute the pronumerals used within the question to clearly explain the changes required.

Areas for students to improve include:

• interpreting proportional and inverse proportional relationships between variables within an equation
• clearly identifying any symbols or pronumerals used in calculations that are not in the information supplied.

Question 28(a)(b)

In better responses, students were able to:

• provide the appropriate equations
• show the correct substitution of the given values into the appropriate equation, and calculate the correct answer

Areas for students to improve include:

• correctly substituting in all the given values into the appropriate equation including the magnetic field strength even though it had a unit value
• checking over working to identify simple errors.

Question 28(c)

In better responses, students were able to:

• explain the forces on the rod in the magnetic field when the field is on, and when the field is off
• explain how induction and Lenz’s law are applied to the rod moving in the magnetic field
• identify clearly the net effect on the force that pushes the rod.

Areas for students to improve include:

• answering all parts of the question, including the effect on the force pushing the rod
• expressing the answer in a clear manner with no contradictions.

Question 29(a)

In better responses, students were able to:

• correctly link each observation to the hypothesis and explain why it did not support gamma as being the unknown radiation.

Areas for students to improve include:

• providing clear cause and effect when making an explanation as to why the hypothesis is rejected
• ensuring that the information supplied in the question is directly addressed in the answer, that is, all three observations needed to be linked to the rejected hypothesis.

Question 29(b)

In better responses, students were able to:

• clearly identify that the neutron is the particle that the experiment produced and that this particle changes the model of the atom by changing the atomic mass or by adding the neutron to the nucleus.

Areas for students to improve include:

• recalling how experimental evidence is use to support changes to the model of the atom over time.

Question 30(a)

In better responses, students were able to:

• provide a relevant example of experimental evidence
• use cause and effect statements to provide a coherent explanation.

Areas for students to improve include:

• demonstrating a clear link between the result of an experiment and how it supports a named aspect of the Standard Model of Matter.

Question 30(b)(i)

In better responses, students were able to:

• apply a correct method to calculate the wavelength
• correctly identify relevant data from the data sheet.

Areas for students to improve include:

• identifying the relevant equation
• accurately substituting data into the equation.

Question 30(b)(ii)

In better responses, students were able to:

• use cause and effect statements to provide a coherent explanation
• demonstrate their understanding of relativity.

Areas for students to improve include:

• correctly using specific physics terms.

Question 31(a)

In better responses, students were able to:

• apply the law of conservation of mechanical energy to account for the changes in the velocity of the comet for the complete orbit.

Areas for students to improve include:

• demonstrating a clear understanding of how the law of conservation of energy applies to an elliptical orbit
• explaining clearly the relationship between gravitational potential energy and kinetic energy to the different positions in the elliptical orbit.

Question 31(b)

In better responses, students were able to:

• identify and equate relevant equations
• apply a correct method to derive an expression for the speed of star B.

Areas for students to improve include:

• ensuring that the correct concept is being analysed, in this case forces rather than energy
• manipulating equations carefully to derive an expression
• setting out derivations clearly and logically.

Question 32

In better responses, students were able to:

• explain in multiple ways, using a cause and effect, how the motion of the mass was limited
• establish the link between the motor and the mass
• relate how the action of the motor affected the mass and vice versa
• use equations and graphs as mathematical models
• use a vector diagram to support explanations.

Areas for students to improve include:

• providing more than one factor when factors are required in the question
• recognising that mathematical models are equations
• differentiating between the terms force and torque
• translating the information correctly from the scenario into the relevant formula.

Question 33

In better responses, students were able to:

• answer all aspects of the question in both sections XY and YZ
• use the terms referred to in the question
• use and analyse the stimulus data correctly
• identify the energy transformation within the cylinder
• manipulate the equation using the data from the question
• use the data to explain the motion
• explain the action of the forces on the motion.

Areas for students to improve include:

• interpreting displacement versus time graphs
• relating energy conservation to motion
• using correct units
• use correct terms, for example, accelerates due to gravity rather than falls due to gravity.

Question 34(a)(b)

In better responses, students were able to:

• recognise that the work done is related to both electric field strength and displacement within the field
• determine that the E field is halved when the plate separation is doubled
• use systematic labelling of the various quantities (particularly vertical and horizontal distances) to avoid confusion when doing algebraic working.

Areas for students to improve include:

• recognising the difference between the effects of electric and magnetic fields on charged particles
• identifying that the nature of the scenario in part b was of projectile rather than circular motion.