Nara Public High School Entrance Examination - Science common mistakes
Nara Public High School Entrance Examination - Science · Understand the traps and how to avoid them.
When asked to find the resultant force or describe motion, the candidate adds or subtracts force magnitudes while ignoring their directions, or treats a balanced pair of forces as producing acceleration.
The candidate memorizes 'resultant = sum of forces' as an arithmetic rule and never draws a force diagram, so opposing forces are handled as if all point the same way; the idea that zero resultant means constant velocity (including rest) is not connected to the calculation.
What to do instead
Before computing, always draw arrows for each force with a stated positive direction, then sum with signs. Practise three patterns until automatic: same direction (add), opposite (subtract, keep sign of larger), perpendicular (Pythagoras). Then state the motion conclusion separately: zero resultant → rest or uniform motion; nonzero → acceleration in the resultant's direction.
On a distance–time or speed–time graph, the candidate reads the height of the line as speed on a distance–time graph, or reads the slope as distance on a speed–time graph, and cannot convert between the two graph types.
The candidate learns 'graph questions = read the value off the axis' and never distinguishes what the gradient and the area represent, so the two graph types blur together and only the vertical axis is used.
What to do instead
Build a two-column table for each graph type: what the gradient means and what the area under the line means. On distance–time, gradient = speed, horizontal line = at rest. On speed–time, gradient = acceleration, area = distance travelled. Drill by describing one motion (e.g. accelerate, cruise, brake) in words, then sketching both graphs for it and checking they agree.
The candidate calculates electrical power or energy by mixing up the formulas P = VI, P = I²R and P = V²/R, or uses the total voltage across a series circuit for a single resistor.
The three power expressions are memorized as separate formulas without the derivation from V = IR, so the candidate does not see that they are interchangeable only when the V and I used belong to the same component; substituting a supply voltage into a single-resistor calculation is not recognised as an error.
What to do instead
Always label each component with its own V, I and R before substituting, and write the target quantity with its unit. Derive P = I²R and P = V²/R once from P = VI and V = IR so the substitution is understood. In series circuits, note that current is common and voltage divides; in parallel, voltage is common and current divides. Check the answer by computing power a second way and comparing.
When describing a wave, the candidate confuses frequency, wavelength and wave speed, and claims that changing the frequency of a wave in the same medium changes its speed.
The relationship v = fλ is learned as a formula to plug numbers into, not as a constraint; the candidate does not know that speed is set by the medium, so an increase in frequency must shorten the wavelength.
What to do instead
State the rule in words first: in a given medium the speed is fixed, so f and λ trade off. Practise problems where a wave crosses from one medium to another (speed changes, frequency stays the same, wavelength changes) and problems where only the source changes (frequency changes, speed fixed). Sketch the wave before and after in each case.
The candidate classifies a change as chemical or physical by whether 'something looks different', so dissolving, melting and colour change from mixing are misjudged, and a precipitate or gas is not recognised as evidence of a chemical change.
The criterion used is visual appearance rather than whether new substances form; the candidate has not internalized that dissolving and state changes are physical even when appearance changes markedly, while a new substance with different properties is the decisive test.
What to do instead
Apply a fixed checklist: did a new substance with different properties form? Evidence includes gas evolution not caused by heating, precipitate formation, and colour change that cannot be reversed by simple physical means. Test reversibility: melting and dissolving can usually be reversed by cooling or evaporating. Sort a list of ten everyday changes using the checklist and justify each in one sentence.
The candidate writes or balances a chemical equation by adjusting subscripts inside formulas (e.g. changing H₂O to H₂O₂) instead of placing coefficients in front of the formulas.
The candidate treats balancing as making the numbers match on both sides, without the rule that a formula represents a fixed substance and may not be altered; the conservation-of-atoms logic behind coefficients is not explicit.
What to do instead
Follow a strict procedure: write correct formulas first, then count each element on both sides in a table, then change only coefficients, re-counting after each change. Finish by checking that every element's count matches and that coefficients are the smallest whole numbers. Practise with a table of atom counts beside each equation so the constraint is visible.
The candidate explains a food chain or ecosystem question by naming organisms but never identifies the direction of energy flow, and treats decomposers as a separate trophic level outside the chain.
Food chains are memorized as sequences of names ('grass → rabbit → fox') without the underlying idea that arrows show transfer of matter and energy, and that most energy is lost at each step, so questions about energy loss or decomposers are answered by recall rather than reasoning.
What to do instead
For every food chain, write the arrow as 'is eaten by' and annotate each step with the energy lost as heat and waste. Place decomposers explicitly as recyclers that return nutrients to producers, not as a fourth consumer level. Practise explaining why a top predator supports fewer individuals than the producers, using the idea of energy decreasing along the chain.
The candidate confuses the roles of mitosis and meiosis, or describes fertilization and cell division without tracking chromosome number through the cycle.
Both processes are learned as 'cell division' with a list of stages, and the key distinction (chromosome number maintained versus halved) is not anchored to a number, so the candidate cannot say what happens to chromosome count after each step.
What to do instead
Draw one diagram with chromosome counts written at every stage: body cell (2n) → meiosis → gametes (n) → fertilization → zygote (2n) → mitosis → growth. For each process, write its purpose in one line (growth and repair versus producing gametes with half the chromosome number). Redo the diagram from memory and check every count.
The candidate answers questions about seasons, day length or phases of the Moon by citing distance from the Sun or the Earth's shadow, rather than the tilt of the Earth's axis and the geometry of Sun, Earth and Moon.
Everyday experience suggests 'closer means warmer' and 'shadow means eclipse', and the candidate has not separated the three independent geometries: Earth's axial tilt for seasons, Earth's rotation for day and night, and the Moon's orbital position for phases.
What to do instead
Build a single reference sketch and label it: axial tilt causing different sunlight angles and day lengths at different latitudes (seasons), rotation causing day and night, and the Moon's position relative to Sun and Earth causing phases. For each exam question, first name which geometry is involved, then answer. Explicitly note that phases are not caused by Earth's shadow; that is a lunar eclipse.
When interpreting experimental data, the candidate reports a conclusion from a single trial, ignores a control condition, or reads a table without checking units and significant figures on the measuring instrument.
The candidate treats the experiment as a demonstration whose expected result is already known, so data are used to confirm rather than to test; the purpose of a control and of repeated trials is not connected to the claim being made.
What to do instead
Use a fixed four-step write-up for every experiment: what was changed, what was kept the same, what was measured, and how many trials. State conclusions as 'within the range measured' and quote the actual values with units. Before reading any table, note the smallest scale division of the instrument and round accordingly. Identify the control group explicitly and say what it rules out.