Okinawa Public High School Entrance Examination - Science common mistakes
Okinawa Public High School Entrance Examination - Science · Understand the traps and how to avoid them.
Writing the answer to a numerical calculation in physics or chemistry without attaching units, or mixing up units such as N and kg, J and W, or mol and g, and submitting the bare number.
Under time pressure candidates treat the calculation as finished once the digits appear, and they memorize formulas such as W = Fs or density = mass/volume as symbol strings without tracking which quantity each symbol carries. Unit conversion (cm to m, g to kg, mA to A) is also skipped because it feels like extra work.
What to do instead
Adopt a fixed three-step habit for every quantitative item: write the formula, substitute values with units included, then write the answer with its unit and check the unit dimensionally (force must come out in N, energy in J). Before substituting, convert all given values to SI in a single written line. Practise ten mixed problems per week where the only thing graded is unit handling, so the check becomes automatic.
Describing motion by reading position off a distance-time or speed-time graph as if the two axes were interchangeable, for example calling a horizontal segment of a distance-time graph 'stopped accelerating' or reading the slope of a distance-time graph as acceleration.
Candidates memorize 'slope = speed' and 'area = distance' as isolated rules without linking them to which graph is in front of them. Japanese textbooks draw both graph types side by side, and students pattern-match on shape rather than on axis labels.
What to do instead
Before answering, write the axis names at the top of the working space and state aloud which graph type it is. Use a two-row reference table built by the candidate: distance-time gives slope = speed, horizontal = at rest; speed-time gives slope = acceleration, area = distance, horizontal = constant speed. Redraw the given graph as the other type and check the two agree.
Balancing a chemical equation by changing subscripts in a formula (turning H2O into H2O2 or Fe2O3 into FeO) instead of adjusting coefficients, or leaving an equation unbalanced after counting atoms only on the left side.
Students see 'the numbers do not match' and edit the most visible number, which is the subscript inside the formula. They also count atoms on one side only and stop when the reactant side looks right, because the conservation-of-mass idea is recited but not used as a checking tool.
What to do instead
Impose a rule: subscripts are untouchable; only coefficients in front may change. Balance in a fixed order (metals, then non-metals other than H and O, then H, then O last), and finish by writing an atom tally under both sides for each element. Add a one-line sentence 'the total number of each atom is equal on both sides, so mass is conserved' to make the principle explicit.
Treating 'dissolved', 'molten', 'aqueous', and 'solid' as interchangeable when deciding whether a substance conducts electricity or takes part in an ion reaction, so that solid NaCl is described as conducting or sugar solution as an electrolyte.
The ionic-bond topic is taught with the words 'ions' and 'conducts' close together, and candidates collapse them into one idea. The distinction between ions being present and ions being free to move is a model-level idea that is easy to state and hard to apply.
What to do instead
Build a three-column table (substance / state / conducts or not / reason) covering solid NaCl, molten NaCl, NaCl solution, HCl solution, sugar solution, copper metal, and distilled water. For each entry write the reason in the form 'charged particles are/are not free to move'. When answering, always name the state before judging conductivity.
Explaining inheritance problems by writing only the phenotype ratio (3:1) and ignoring genotype, or assuming a dominant trait must be the more common one in the population, and mis-handling sex-linked or test-cross questions as a result.
The 3:1 ratio is memorized as an answer rather than as an outcome of a Punnett square. Students also confuse 'dominant' with 'frequent', and cross-breeding notation (A, a, AA, Aa) is used loosely without defining which letter stands for which allele.
What to do instead
Always define the symbols first in writing (let A = dominant allele, a = recessive allele), draw the full Punnett square, and report genotype ratio and phenotype ratio separately. Add a sentence distinguishing dominance from frequency. For test crosses, state that crossing with a recessive homozygote reveals the unknown genotype, and check the conclusion against the square.
Confusing the roles of producers, consumers, and decomposers in a food web, or drawing an energy pyramid as if energy passed upward undiminished, and describing a food chain without arrows pointing in the direction of energy flow.
The vocabulary is learned as labels rather than as a flow model. Candidates draw arrows from predator to prey because that reads like 'eaten by', and they treat decomposers as a side category outside the cycle.
What to do instead
Draw every food web with arrows meaning 'is eaten by / energy flows to' and say the direction aloud. Write the carbon or nitrogen cycle as a loop that includes decomposers returning inorganic matter to producers. For pyramids, state explicitly that energy decreases at each level while matter cycles, and give a numerical example (for example 10 percent transfer) to anchor the idea.
Reading a seismogram or a geological cross-section by identifying the fastest wave as the most destructive, or ordering rock layers by position without checking for faults, folds, and intrusions that cut across them.
P-wave and S-wave properties are memorized as a list, and the principle of superposition is applied mechanically. Students do not look for cross-cutting relationships, which is the actual reasoning the item is testing.
What to do instead
For wave questions, write a two-row table (P wave: fastest, passes through solids and liquids; S wave: slower, solids only) and connect arrival-time difference to distance. For cross-sections, apply a written checklist: are any layers cut by a fault or intruded by magma, and therefore younger than what they cut? State the relative age of each labelled unit in order before answering.
Explaining seasonal change, day length, or the apparent motion of stars by saying 'the Earth is closer to the Sun in summer' or by confusing rotation with revolution, and drawing the Earth's axis as perpendicular to the orbital plane.
Everyday experience suggests distance controls warmth, and rotation and revolution are both 'spinning' in casual language. Diagrams in notes are often drawn without the 23.4-degree tilt, so the tilt is not available as an explanatory tool.
What to do instead
Redraw the orbit diagram by hand with the axis tilted and parallel to itself at four positions, and label the solstices and equinoxes. Write one sentence for each season naming the cause as the angle of sunlight and day length, not distance. Keep a two-line definition card: rotation = one day, causes day and night; revolution = one year, with tilt, causes seasons.
In observation and experiment items, recording results that contradict the hypothesis as 'the experiment failed' or altering the data to fit, and omitting the control condition or the variable being changed when describing the method.
School practicals reward reaching the textbook result, so candidates learn that a mismatch means error rather than information. Experimental design language (control, independent variable, dependent variable, constant conditions) is recited but not applied when writing a procedure.
What to do instead
Use a four-line planning frame for every experiment item: what I change, what I measure, what I keep constant, and what I compare against. When results differ from the prediction, write 'the hypothesis is not supported' and propose one concrete cause and one follow-up measurement. Practise by rewriting three given procedures into the four-line frame.
Reporting a measured value with excessive significant figures or no consideration of instrument precision, and calculating an average without discarding or explaining anomalous readings.
Calculators return many digits and candidates copy them all. The idea that a reading from a ruler marked in millimetres is uncertain at the next digit is rarely practised, and outliers are averaged in because 'all data must be used'.
What to do instead
Set a rule before calculating: state the smallest division of the instrument, record to one estimated digit beyond it, and round the final answer to match. When averaging, list all readings, circle any that differ markedly, and write whether it is excluded and why. Do five short data-processing drills per week where the marking scheme is precision and outlier handling only.