Wakayama Prefectural Public High School Entrance Examination - Science common mistakes
Wakayama Prefectural Public High School Entrance Examination - Science · Understand the traps and how to avoid them.
When calculating density or concentration, students plug the mass in grams and the volume in cm³ straight into a formula without checking that the units match, and write the answer as a bare number with no unit (for example writing 2.7 instead of 2.7 g/cm³).
In the unit on mass and volume, students practise density = mass ÷ volume so often that the calculation becomes mechanical, and they stop tracking which quantity is which. Because the prefectural exam often gives volume in cm³ but occasionally converts to m³ or mL, students who have memorised only the numerical procedure cannot tell which unit the answer should carry.
What to do instead
Before substituting numbers, always write the formula with the units attached (density [g/cm³] = mass [g] ÷ volume [cm³]), and convert units in a separate step first. Check the answer against a rough estimate, and make it a habit to write the unit on every answer line, including in the working.
Students describe the result of a chemical reaction by writing the names of the substances (for example 'hydrogen and oxygen were produced') instead of writing the chemical formulas and a balanced equation, and they do not balance the atoms on the two sides.
In the unit on chemical changes and atoms/molecules, students memorise the observations from experiments (a gas was produced, a precipitate formed) but do not internalise the meaning of the law of conservation of mass. Under exam pressure they fall back on the descriptive wording they remember from the textbook, and they do not have the habit of counting atoms on each side.
What to do instead
For every reaction, practise the fixed sequence: write the formulas of the reactants and products, then count each element on both sides, then adjust the coefficients. Check that the total number of atoms of each element is the same on both sides, and write a sentence explaining that this is the law of conservation of mass.
In questions about force and motion, students assume that a force is acting whenever an object is moving, or that the forces must be unbalanced while the object moves at a constant speed, and they draw the arrows of force as if they all pointed in the direction of motion.
Everyday experience suggests that you have to keep pushing something to keep it moving, so students carry an Aristotelian intuition into the unit on force and motion. They also confuse 'moving' with 'accelerating' and do not reliably connect the idea of balanced forces to the state of rest or of uniform motion.
What to do instead
For each problem, first identify the object's state of motion (at rest, constant speed, or changing speed), then decide whether the forces are balanced or unbalanced. Draw a free-body diagram with all the forces acting on the object, and check that the arrows match the state of motion you identified.
When drawing ray diagrams for light or interpreting a circuit diagram, students draw the rays without arrowheads, or they treat the image formed by a convex lens as always real, or they read a circuit as if current is used up as it passes through each resistor in turn.
In the unit on light, sound, and current, students learn the rules for ray diagrams and for series and parallel circuits as separate facts, without a single underlying model. Because the prefectural exam often asks students to choose between several diagrams, students who have not internalised the model cannot reject the wrong options.
What to do instead
Redraw ray diagrams yourself with arrowheads and check the three principal rays for a lens. For circuits, always trace the current from the positive terminal and mark the junctions, and confirm that the current is the same at every point in a series circuit and splits at a parallel junction. Practise explaining in words why each wrong option is wrong.
In questions on organisms and life processes, students describe a observation such as 'the starch disappeared' or 'the colour changed' without naming the substance, the reagent, or the control experiment, and they confuse the roles of the independent and controlled variables.
In the unit on organisms and life processes, students learn the experimental procedures as a list of steps to memorise, not as a design with variables. When the exam asks them to evaluate an experimental method or to state a control, they cannot identify which condition was deliberately varied.
What to do instead
For each experiment, write down the question being tested, the variable being changed, the variables held constant, and the control. State results in terms of named substances and reagents (for example 'starch was broken down, so iodine solution did not turn blue-black'), and always say what the control shows.
In earth and space questions, students treat the phases of the Moon, the seasons, and eclipses as if they were caused by the same thing, for example saying that summer happens because the Earth is closer to the Sun, or that a lunar eclipse happens every month.
In the unit on the Earth and space, the three phenomena are taught close together, and students merge them into one vague idea of 'the Earth moves around the Sun'. They also underestimate the tilt of the Earth's axis and the inclination of the Moon's orbit, which are the key points.
What to do instead
Build a clear model for each phenomenon separately: the seasons come from the tilt of the Earth's axis, the phases of the Moon come from the angle between the Sun, the Moon, and the Earth, and eclipses require the Sun, the Earth, and the Moon to be nearly in a straight line. Draw a diagram for each case and state the cause in one sentence.
Students write numerical answers with the wrong number of significant figures or round too early in a multi-step calculation, and they omit the working, so partial credit cannot be awarded when the final value is wrong.
In the physical science units, students focus on getting a single number and treat the working as scrap paper. In the prefectural exam, marks are often given for the method, and rounding intermediate values (for example in a density or speed calculation) shifts the final answer outside the accepted range.
What to do instead
Keep one extra digit through intermediate steps and round only at the end. Write every step with its units on the answer sheet, and check the final answer against a rough estimate made before calculating.
Students answer 'describe what happens' questions with a single word or a phrase copied from the question, instead of a complete sentence that names the cause and the result, and they do not use the technical terms the mark scheme expects.
Under time pressure, students write the shortest possible answer and assume the marker will infer the rest. In the prefectural exam, explanation questions are marked against specific key words, and a phrase that merely restates the question earns no credit.
What to do instead
Practise the pattern 'because [cause], [result]'. After writing an answer, check that it contains at least one technical term from the unit and that it would still make sense to someone who had not read the question.
Students confuse the particle model with the macroscopic observation, for example saying that 'the particles expand' when a substance is heated, or that 'the particles melt' when ice turns to water.
In the unit on matter and particles, the diagrams of particles are drawn at a larger scale than the real particles, and students describe what the diagram looks like rather than what the particles do. They do not separate the behaviour of the particles from the behaviour of the bulk substance.
What to do instead
Always state the change at the level of the particles and at the level of the substance separately: the particles gain kinetic energy and move faster, while the substance expands or changes state. Check every sentence for the subject: is it the particle or the substance that is doing the action?
Students do not read the question's conditions carefully and answer a different question, for example giving the total resistance when the question asks for the current through one resistor, or describing the reaction of a metal with acid when the question asks about a metal with a salt solution.
In the unit on light, sound, and current and in the unit on chemical reactions, many questions look similar and differ only in one condition. Students recognise the familiar diagram and answer from memory without checking the specific quantities or substances asked for.
What to do instead
Underline the quantity or substance the question asks for and the conditions given before starting to calculate. After writing the answer, reread the question and confirm that the answer matches what was asked, not what the diagram reminded you of.