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Assessment Report
Level 3 Physics 2017
Standards 91523 91524 91526
Part A: Commentary
Most candidates attempted all questions and wrote significant amounts for the more difficult explanation questions. In general, candidates showed greater competence in solving problems that required calculations than those that required written explanations. Candidates frequently failed to fully address the specifics of the question asked, giving explanations of the general case rather than relating concepts to details of the specific case. Many candidates would also have improved their answers had they drawn diagrams to help demonstrate their understanding. Trigonometric problem solving, such as vector addition, SHM reference circles, and AC phasor diagrams are consistently poorly attempted by candidates achieving below merit level. However when attempted, they are frequently correctly drawn.
Level 3 Physics requires careful use of precise language and inclusion of relevant details linked to the specific situation given in the context to achieve with excellence.
Part B: Report on standards
91523: Demonstrate understanding of wave systems
Candidates who were awarded Achievement commonly:
 calculated wavelengths and frequencies
 related beats to interference
 sketched wave forms of different harmonics on strings and pipes
 labelled nodes and antinodes on diagrams of standing waves
 identified the speed of sound and the speed of light correctly.
Candidates who were assessed as Not Achieved commonly:
 showed insufficient working in calculations
 used calculators in radian mode when inputting angles in degrees
 could not describe the Doppler effect using physics terms
 confused the term ‘node’ with ‘destructive interference’ and ‘trough’
 confused the term ‘antinode’ with ‘constructive interference’ and ‘crest’
 drew fixedend wave forms when openend were required or visa versa
 did not attempt more difficult questions.
Candidates who were awarded Achievement with Merit commonly:
 communicated understanding through labelled diagrams
 demonstrated clear logic through sufficient working for ‘show’ calculations
 wrote accurate explanations but omitted essential details to demonstrate a thorough understanding of wave concepts
 explained how the movement of a wave source changes the wavelength in Doppler effect applications
 linked the colour of light to wavelength to explain changes to patterns formed by passing different colours of light through diffraction gratings
 failed to distinguish between the central maxima and the first order antinode.
Candidates who were awarded Achievement with Excellence commonly:
 explained all aspects of standing wave formation paying close attention to detail
 used accurate, labelled diagrams, equations, in addition to text in explanations
 explained that spectra are seen because different wavelengths of light interfere differently and applied this understanding to calculations
 applied understanding of physics concepts to unfamiliar situations to solve problems and explain observations
 related physics concepts to provide explanation for specific situations or general cases as required.
Standard specific comments
This standard requires very precise use of language and detail. For example, many candidates say; “the path difference is a whole number” rather than “the path difference is a whole number multiple of wavelength”, ‘the first harmonic is a quarter of a wavelength’ rather than ‘the length of the pipe is one quarter of the wavelength”, and “out of phase” (which could mean anything not 100% in phase) rather than “180^{o }out of phase”. Candidates must carefully read the question and ensure they have fully answered the question and with sufficient detail.
91524: Demonstrate understanding of mechanical systems
Candidates who were awarded Achievement commonly:
 used relevant equations in a onestep calculation, sometimes when amore complex calculation was required
 selected correct problem solving methods, but made calculation mistakes
 recognised the centre of mass moves with constant velocity before and after a collision with no external forces
 described changes in force and potential energy as orbit radii decreased
 equated gravitational force with centripetal force for orbiting objects
 described relationships between mass, radii, rotational inertia, and angular velocity in situations where angular momentum is conserved
 described conditions required for simple harmonic motion
 drew accurate reference circle diagrams
 identified limitations of a model compared to the reality of a situation.
Candidates who were assessed as Not Achieved commonly:
 struggled to select and apply equations in single step calculations
 could not calculate the position of the centre of mass or describe the motion of the centre of mass
 failed to recognise the vector nature of momentum, attempting calculations in only one dimension
 confused distance, speed, and momentum definitions and interchanged values in calculations
 selected incorrect equations to solve particular problems
 used irrelevant equations in explanations
 failed to describe relationships between mass distribution, rotational inertia, torque, and angular acceleration
 thought that rotational kinetic energy is conserved rather than angular momentum
 lacked knowledge of the conditions of SHM, SHM equations, or SHM graphs.
Candidates who were awarded Achievement with Merit commonly:
 calculated position of the centre of mass of a system
 added momentum vectors using vector addition processes
 had correct method, but made minor errors in substitution or algebra
 linked changes in one quantity to changes in another for applications involving a conservation law
 drew velocity vs time graphs for SHM including a calculated maximum velocity
 used linking words in explanations showing that one event causes another event
 did not fully address questions, such as simply drawing a sinusoidal graph for SHM when the question asked to start the graph from the lowest point.
Candidates who were awarded Achievement with Excellence commonly:
 were able to perform multistep calculations using correct formula, selecting appropriate data, and gave answers with correct units
 distinguished between different conservation laws and clearly stated which quantities were increasing, decreasing, and staying constant in particular situations
 justified use of specific conservation laws by identifying that no external, unbalanced forces and/or torques existed
 were able to articulate the assumptions made to simplify calculations.
Standard specific comments
Many candidates struggled with the concept of centre of mass, frequently misidentified forces – particularly gravitational force and tension, and held significant misconceptions around the application of conservation of energy when applied to rotational kinematics. Algebraic skills involving trigonometry were challenging for many candidates, particularly the concept that sin ωt ≠sin t norω sin t nor t sinω.
91526: Demonstrate understanding of electrical systems
Candidates who were awarded Achievement commonly:
 used formula to calculate basic values
 described and calculated time constant
 described how current changes as a capacitor charges
 calculated combined capacitance
 knew that a changing current creates a changing magnetic flux
 explained how an inductor induced an opposing EMF
 converted between RMS and peak voltage
 calculated the impedance of a LR circuit
 described the effect of increasing the dielectric constant for a capacitor on capacitance
 showed basic understanding of characteristics of LCR circuits.
Candidates who were assessed as Not Achieved commonly:
 did not know the meaning of time constant for a capacitor
 thought that energy was lost in a circuit because the voltage had to pass through a resistor first
 stated that protons move onto the positive plate of a capacitor to give it a positive charge
 described charging a capacitor as increasing its internal resistance
 made calculation errors such as forgetting to square or square root values in equations
 square rooted entire blocks of numbers instead of just the values stated in the formula
 confused charge with capacitance
 confused inductance with reactance
 thought that inductors create an opposing current to oppose a supply voltage
 could not draw a phasor diagram to represent relationships in AC circuits.
Candidates who were awarded Achievement with Merit commonly:
 described energy, charge, and current relationships for charging capacitors
 linked changes in capacitance and time constant to the adding capacitors in parallel
 explained how voltage is induced in the secondary coil of a transformer
 explained why current slowly increases when an inductor is connected in parallel
 calculated the inductance of circuits by determining the rate of chance of current from d vs t graphs
 explained why a spark could be produced when a switch is opened in a circuit
 calculated resonant frequencies of LCR circuits and explained why current is maximum at resonance.
Candidates who were awarded Achievement with Excellence commonly:
 demonstrated a good understanding of the three stages of charging a capacitor and explained the exponential shape of the sketched graph
 gave a thorough explanation of how an inductor affects the current and why a spark is produced when the switch is opened
 calculated the resonant frequency of an LCR circuit and explain why the current is maximum at resonance.
Standard specific comments
Many candidates demonstrated misconceptions in their understanding of inductors. Many described an ‘induced current’ opposing the circuit current rather than an induced opposing voltage.
Physics subject page
Previous years' reports
2016 (PDF, 243KB)