Tochigi Public High School Entrance Examination - Science common mistakes
Tochigi Public High School Entrance Examination - Science · Understand the traps and how to avoid them.
Writing the direction of a force or current without stating the reference (e.g., 'the force is downward' or 'the current flows right') instead of naming it relative to the page, the observer, or the circuit, and leaving vector answers as bare numbers with no arrow or sign.
Students memorize 'friction opposes motion' and 'current goes from plus to minus' as slogans and then apply them without drawing the situation, so the reference frame stays implicit. Under time pressure they skip the free-body sketch or the circuit arrow, and the answer becomes ambiguous even when the physics idea is right.
What to do instead
Before writing any force or current direction, draw the object or the circuit loop and mark a fixed reference (e.g., 'to the right on the page', 'clockwise seen from above'). Label each force with its source (gravity, normal, friction) and give current direction in terms of the external circuit from the positive terminal. Practice by re-answering past-style items where only the direction was wrong and check that your stated direction survives without the diagram.
Treating 'velocity' and 'speed', or 'displacement' and 'distance', as interchangeable in calculations, and averaging speeds arithmetically (e.g., (v1+v2)/2) over equal distances rather than using total distance over total time.
Everyday language uses 'speed' for both, and the textbook distinction is introduced once and then assumed. Students also pattern-match 'average' to the arithmetic mean, which is correct only for equal time intervals, not equal distances.
What to do instead
Adopt a rule: on any motion problem, first write the quantity asked for with its symbol and unit (v, m/s, a vector; s, m, a scalar) and decide whether direction matters. For averages, always compute total distance ÷ total time and check with a numerical example where the two legs differ (e.g., 30 km/h out, 60 km/h back gives 40 km/h, not 45). Redo one such problem each week until the distinction is automatic.
Assuming a moving object always has a force in the direction of motion, or that zero net force means zero velocity, so students mark 'a force acts forward on a ball at the top of its flight' or claim a puck sliding at constant speed has a net forward force.
Aristotelian intuition ('motion needs a push') survives instruction because most everyday motion does involve friction or propulsion. Students also conflate Newton's first law (zero net force ⇔ constant velocity, including zero) with 'zero net force ⇔ at rest'.
What to do instead
Drill the first law as an equivalence: net force zero ⇔ velocity constant (which includes v = 0). For any dynamics item, draw the free-body diagram first and only then write ΣF = ma; if a = 0, state explicitly that the forces balance and no forward force is needed. Use the 'ball at the top of its path' and 'ice puck' cases as standard checks before answering.
Mixing up energy conservation and force balance: writing 'energy is conserved, so the speed is constant', or equating potential energy lost to kinetic energy gained while ignoring work done against friction, and confusing power (W) with energy (J) in answers.
Both principles are taught as 'nothing is lost', so students merge them. They also drop the friction term because it complicates the algebra, and they treat watt and joule as the same 'amount of energy' because both appear in appliance labels.
What to do instead
Write the energy statement explicitly as a ledger: E_initial = E_final + W_friction (or heat), with each term in joules and units shown. Keep a one-line definition card: energy = capacity to do work (J); power = energy per second (W = J/s). When a problem gives time and a power rating, multiply P × t to get energy before comparing. Check every energy answer by asking whether anything left the system as heat or sound.
Reading a wave graph without checking what the horizontal axis represents, so wavelength is read off a displacement–time graph, or frequency is read off a displacement–distance graph; also describing reflection/refraction with the angle to the surface instead of the angle to the normal.
Textbook figures alternate between y–x and y–t plots with similar shapes, and students recognize the shape rather than the axis label. For angles, diagrams often draw the angle to the mirror because it is visually obvious, and students copy that.
What to do instead
Before extracting any value, say aloud (or write) what the axes are and what one full cycle means on that axis. Use the rule: y–x gives wavelength λ (m) and wave speed via v = fλ; y–t gives period T (s) and f = 1/T. For optics and reflection, always draw the normal as a dashed line first and measure angles from it, then convert if the question gives the angle to the surface (90° − θ).
Applying Ohm's law to a whole circuit while ignoring series/parallel structure, e.g., adding resistances in parallel by simple sum, or assuming current is 'used up' as it passes through each resistor so later components get less current.
The formula V = IR is over-learned as a plug-in, and the 'water flowing through pipes' analogy suggests current is consumed. Students also memorize the series rule and misapply it to parallel branches because both rules look like 'combine the resistors'.
What to do instead
Solve circuits in a fixed order: mark junctions, identify series segments (same current) and parallel branches (same voltage), reduce to one equivalent resistance, find the total current from the source, then work back branch by branch. State the conservation fact explicitly: current entering a junction equals current leaving, so a series loop carries the same current everywhere. Practise two-resistor circuits until you can predict which resistor has the larger current before calculating.
Describing matter at the particle level with vague words ('the particles melt', 'the atoms expand') instead of naming the change in arrangement, motion, or spacing; and treating dissolving as a chemical change or a mixture as a compound.
State changes and dissolving look like 'the substance changes', and students lack a precise particle vocabulary. Curriculum diagrams show particles but students recall the picture, not the model, so they describe what the substance does rather than what the particles do.
What to do instead
Use a fixed sentence frame for every particle explanation: 'The particles gain kinetic energy, so they vibrate/move faster and the spacing between them increases; the particles themselves are unchanged.' For classification, apply tests: a mixture can be separated by physical means and keeps component properties; a compound has a fixed ratio and new properties; dissolving is physical. Sort ten everyday examples into element/compound/mixture and justify each with one of these tests.
Balancing an equation by changing subscripts (turning H2O into H2O2 or Fe2O3 into FeO) or by 'fixing' only one element, and then reading the coefficients as masses rather than mole ratios in quantitative problems.
Students see balancing as making the two sides 'look equal' and reach for the fastest visual fix, which is editing subscripts. Because the mole concept is abstract, they also carry coefficients straight into gram calculations without converting.
What to do instead
Impose a hard rule: subscripts are identity, coefficients are the only thing you may change; if the count will not balance, the formula is fixed and you must add coefficients. Balance in order: metals, non-metals, hydrogen, oxygen last; then verify each element count. For quantitative work, always convert mass → moles (n = m/M) before using coefficients, then convert back, and write the unit at each step so a gram answer cannot come out of a mole ratio.
Confusing meiosis and mitosis, or describing inheritance as 'the child gets half from each parent' without distinguishing genotype from phenotype, dominant from recessive, and homologous chromosomes from sister chromatids; predicting offspring ratios from a single example rather than a Punnett square.
Both divisions are 'cell division', and the vocabulary (chromosome, chromatid, gene, allele) is introduced densely. Students also carry the everyday idea that a dominant trait is 'more common' or 'stronger', which is wrong, and they generalize from one family's outcome.
What to do instead
Build a comparison table once and reuse it: mitosis - one division, identical diploid cells, growth/repair; meiosis - two divisions, four haploid gametes, variation via independent assortment and crossing over. Define dominant as 'expressed when one copy is present', not 'more frequent'. For every genetics problem, write parental genotypes, draw the Punnett square, then state genotype and phenotype ratios separately. Re-answer one dihybrid or test-cross item to confirm the square, not intuition, drives the ratio.
Explaining population change with single causes ('more predators, so fewer prey') without following the chain through food webs, and ignoring that energy is lost at each trophic level, so top predators are described as receiving 'the most energy'.
Food-web diagrams look static and students read arrows as 'eats' without direction conventions (arrow points to the consumer). The 10% energy idea is memorized as a number but not connected to why food chains are short and why biomass pyramids narrow.
What to do instead
State the arrow convention explicitly (A → B means energy flows from A to B) and trace one change through at least three links before writing an answer. Keep the energy rule with its consequence: only about 10% passes to the next level, so higher levels hold less energy and biomass, and chains are short. Practise by removing one species from a web and predicting two separate effects, then check both against the arrow directions.
Reading a geologic cross-section or rock record without applying superposition and cross-cutting relationships, so students call an intrusion older than the layers it cuts, or treat a fold as evidence that the rock is young rather than that it was deformed after deposition.
Relative dating rules are stated in one lesson and then never practised on unfamiliar diagrams. Students reason from appearance ('the intrusion looks like it grew through, so it must be newer' is right, but they invert it) or from the label order rather than from the geometry.
What to do instead
Apply the rules in a fixed sequence: (1) undisturbed layers - lowest is oldest (superposition); (2) a feature that cuts another is younger than what it cuts; (3) inclusions are older than the rock containing them; (4) folding/faulting postdates the layers it affects. On any cross-section, number the events 1, 2, 3… before answering. Redo one diagram where the intrusion is drawn ambiguously and justify each ordering step in writing.
Explaining seasons by Earth's changing distance from the Sun, or explaining day and night length with the Earth's rotation period rather than the tilt of its axis; also confusing rotation with revolution when describing the cause of a year or a day.
The orbit diagram is an ellipse, which invites a distance explanation, and 'closer means warmer' is a strong everyday intuition. The tilt is a small detail in a crowded diagram, so it is forgotten and rotation/revolution are swapped verbally.
What to do instead
Use a single causal chain and write it out: axial tilt (about 23.4°) → changing angle of sunlight and day length → seasons; distance variation is small and does not cause seasons. Keep a two-line card: rotation = one turn on the axis = day/night; revolution = one orbit = year. Test yourself with the counter-example: both hemispheres have summer at opposite times, which distance alone cannot explain.
Writing conclusions that go beyond the data ('this proves plants need light to grow' from one trial) or treating a single measurement as reliable; failing to identify the variable deliberately changed, the variables held constant, and the control, and describing a graph as 'going up' without stating the relationship and its range.
Students are rewarded in everyday writing for strong claims and have little practice separating observation from inference. Experimental design terms are memorized as definitions but not applied, so a described method is read as a story rather than a set of variables.
What to do instead
Use a fixed answer frame for every experiment: 'The independent variable was X; Y and Z were held constant; the control was…; the data show that as X increases, Y increases/decreases over the range …; this supports/does not support the hypothesis because…'. Avoid the words 'prove' and 'always'; use 'supports' and state the tested range. Practise by rewriting three over-claiming conclusions into data-limited ones and checking that each names the evidence.