New Zealand Scholarship Physics common mistakes
New Zealand Scholarship Physics · Understand the traps and how to avoid them.
Presenting a derivation as a string of equations with no stated starting principle, so the marker cannot see which physical law justifies the first line or the algebraic steps that follow.
Scholarship Physics rewards evidence of reasoning, not just a correct final value. Candidates who have practised on shorter answer formats carry over the habit of jumping straight to algebra, and under time pressure they drop the justification sentences first.
What to do instead
Before writing any algebra, write one sentence naming the principle and the system it applies to (for example, 'Applying conservation of angular momentum to the disc plus the dropped mass about the axle'). Then annotate each major step with a short clause explaining what was substituted or assumed. Practise by writing full solutions to past-style derivations and marking your own work against the criterion 'could a reader follow this without me?'
Treating a multi-part question as independent parts and never linking the result of an earlier part to a later one, even when the later part clearly depends on the earlier answer.
Candidates read and answer each part in isolation, especially when the earlier part produced an unfamiliar expression. They may also distrust their own earlier result and re-derive from scratch, wasting time and sometimes contradicting themselves.
What to do instead
After reading the whole question, sketch a dependency map: which quantity produced in part (a) is used in parts (c) and (d). If an earlier result is an algebraic expression, carry it forward symbolically rather than substituting a number. If you believe an earlier answer is wrong, state the corrected value explicitly and continue consistently rather than silently switching.
Giving a numerical answer with no uncertainty, no significant-figure discipline, and no check that the magnitude is physically sensible.
School-level habits encourage 'the answer' as a single number. Scholarship-level questions often involve estimated data or approximations, and candidates are not used to propagating uncertainty or commenting on precision.
What to do instead
For every numerical answer, state the value with an appropriate number of significant figures justified by the input data, and add a one-line sanity check (order of magnitude, limiting case, or comparison with a known value). Where inputs are estimates, carry a rough fractional uncertainty through the calculation and quote the result as a range. Build this into your standard answer template so it becomes automatic.
Describing a physical situation in words only, or algebra only, without ever drawing a labelled free-body diagram or field/ray diagram.
Under exam pressure diagrams feel like lost writing time, and many candidates have never been explicitly taught that the diagram itself earns reasoning credit and prevents sign and direction errors.
What to do instead
Make a labelled diagram the first thing you write for any mechanics, fields, or optics problem: define axes, mark forces with arrows and names, mark angles and lengths. Refer to the diagram in your explanation ('the component of tension along the incline is...'). This habit also catches sign errors before they propagate into algebra.
Confusing the direction of an induced effect with the direction of the cause, for example stating that an induced current flows so as to increase the flux change, or that a back-emf aids the applied voltage.
Lenz's law and self-induction are stated in words that are easy to invert, and candidates often memorise the phrase without testing it against a concrete example. The minus sign in Faraday's law is then applied inconsistently.
What to do instead
Always reason from energy conservation: an induced effect must oppose the change that produced it, otherwise energy would be created. For each problem, explicitly state 'the flux is increasing into the page, so the induced current must produce flux out of the page, which means a counter-clockwise current'. Work through at least one example each of a magnet approaching and receding from a coil, and of a circuit being switched on and off.
Applying conservation of energy to a situation where energy is not conserved in the assumed form, for example ignoring work done by friction, by a non-conservative external force, or by a changing mass system.
Candidates default to 'initial energy equals final energy' because it usually works in simpler problems. They fail to check whether the system boundary they have drawn actually encloses all the energy transfers.
What to do instead
Before writing an energy equation, define the system boundary explicitly and list every energy transfer crossing it. If friction acts, include the thermal term. If mass enters or leaves, use momentum or the work-energy theorem for the open system instead. Write the general statement 'change in mechanical energy equals work done by non-conservative forces' and then simplify, rather than starting from the simplified form.
Treating a wave or oscillation problem as if phase, path difference, and phase difference were interchangeable, leading to interference conditions stated as 'path difference equals a whole number of wavelengths' applied to the wrong situation.
The conditions for constructive and destructive interference differ depending on whether there is a phase shift on reflection, and candidates memorise one version. Superposition of two waves with different amplitudes or phases then goes wrong.
What to do instead
Always derive the condition from the superposition of the two waves written as functions of time, including any phase offsets from reflection or source phase. State explicitly whether a phase shift of pi occurs at each boundary. Then the condition follows rather than being recalled. Practise with thin films, double slits, and standing waves on strings to see how the same method gives different-looking results.
Using the photon model and the wave model in the same explanation without acknowledging the apparent contradiction, for example explaining single-photon interference as a classical wave while also invoking photon energy.
Quantum phenomena are taught through both models, and candidates patch together whichever model fits each sentence. Scholarship questions often probe precisely this duality and reward candidates who can articulate the limits of each model.
What to do instead
When a question involves both aspects, structure the answer in two explicit stages: which model predicts what, and how the two are reconciled (for example, the wavefunction gives the probability distribution for individual photon detections). Use language such as 'the classical wave model predicts the fringe pattern, while the photon model explains why the pattern builds up one detection at a time'. Rehearse this for photoelectric effect, double slit, and atomic spectra.
Answering an 'explain' or 'discuss' question with a calculation and no prose, or with prose that restates the question without adding mechanism.
Candidates equate physics with numbers and feel prose is less rigorous. In Scholarship-style marking, however, the explanatory command words carry most of the available credit, and a bare calculation may score little even if correct.
What to do instead
Read the command word before planning: 'calculate' needs working, 'explain' needs a causal chain, 'discuss' needs competing considerations and a judgement. For explain/discuss, write a short plan with the chain of causes, then write full sentences that name the mechanism at each link. Check that every sentence would be false or trivial if deleted; if so, it is filler.
Ignoring the assumptions behind a standard formula, such as applying the ideal gas law to a dense gas, the simple pendulum period to large amplitudes, or the thin-lens equation to a thick lens, without comment.
Formulas are learned as universal tools, and candidates rarely see the derivation that reveals the small-angle or idealisation step. Scholarship questions often deliberately place a system outside the formula's validity to test this awareness.
What to do instead
For each major formula you use, keep a one-line note of its assumptions and check them against the problem data before substituting. If an assumption is violated, say so and either use a corrected approach or state the direction and size of the error. Build a personal 'assumptions sheet' for mechanics, thermal, optics, and electricity, and review it before the exam.