Yamaguchi Prefectural Public High School Entrance Examination - Science common mistakes
Yamaguchi Prefectural Public High School Entrance Examination - Science · Understand the traps and how to avoid them.
When asked to compare the speed of two objects on a distance–time graph, the student reads the height of each line at a single instant and concludes the higher line means the faster object, instead of comparing the slopes.
Everyday language treats 'higher' as 'more', and the vertical axis value is the most visually salient feature. Students have not yet internalised that on a distance–time graph the gradient, not the position, encodes speed, so a line that starts higher but rises slowly is misjudged as faster.
What to do instead
Before answering, redraw the graph and mark slope triangles on two intervals of equal width; compute distance ÷ time for each and write the two numbers next to the lines. Practise with pairs of lines that cross, so the student must state 'A is faster before the crossing, B is faster after' rather than giving one answer for the whole graph.
When a trolley is pushed at constant speed across a bench, the student draws a forward force larger than the friction force, arguing that motion requires a net force in the direction of travel.
The Aristotelian intuition that force is needed to keep something moving is strong and is reinforced by everyday experience of pushing heavy objects, where friction is invisible. Students do not distinguish 'net force determines change of motion' from 'force determines motion'.
What to do instead
Use the constant-speed case as a standing rule: if speed and direction are unchanged, the forces are balanced and the resultant is zero, so forward push equals friction. Have the student draw the two force arrows equal in length and label the resultant as 0 N, then contrast this with the accelerating case in the same diagram pair.
In a circuit with two resistors in series, the student writes that the current is larger in the first resistor than in the second, or that current is 'used up' as it passes through each component.
The water-flow analogy is applied too literally, with current treated as a substance consumed by each load. Students also confuse the potential difference across a component with the current through it, because both are described as 'electricity' in casual speech.
What to do instead
State and apply the series rule explicitly: current is the same at every point in a single loop, and it is the potential difference that is shared in proportion to resistance. Have the student label the current at four points around the loop with the same value and label each voltage drop separately, then check that the drops sum to the supply voltage.
When asked for the total resistance of two resistors in parallel, the student adds them, or when asked which branch carries more current, the student says the larger resistor does.
The series rule was learned first and is over-generalised. The inverse relationship in parallel circuits is not intuitive, and students have not connected parallel branches to the idea that each branch has the full supply voltage across it.
What to do instead
Anchor parallel problems in the voltage statement first: write the supply voltage across each branch, compute each branch current by V ÷ R, then add the branch currents to get the total. Derive the combined resistance from total voltage ÷ total current rather than memorising the reciprocal formula, and compare the result with the smallest individual resistor to confirm it is smaller.
When asked to write the equation for neutralisation of hydrochloric acid with sodium hydroxide, the student writes NaHCl + OH or produces a formula with the wrong subscripts, and then balances it by changing those subscripts.
The student treats chemical formulas as something to be adjusted freely to make the counts match, rather than as fixed facts about which ions combine. Weak recall of valency and of the ions present in solution means the formula is guessed before balancing begins.
What to do instead
Split every equation task into two separate steps written on separate lines: first write correct formulas from ion charges (Na⁺ with Cl⁻, H⁺ with OH⁻), then balance only by placing coefficients in front. Enforce the rule that a subscript may never be altered once written, and check the final equation atom by atom in a table.
After heating a metal in air and finding the product is heavier than the original metal, the student explains the mass gain by saying 'the metal absorbed heat' or 'the flame added mass'.
The student has memorised the law of conservation of mass as a slogan but has not applied it to reactions involving gases. Because the reacting gas is invisible, only the solid is tracked, so the mass change appears to come from the heat source.
What to do instead
Have the student write the word equation including oxygen as a reactant, then mark which reactant came from the air. Use a sealed-vessel comparison: mass is unchanged when the vessel is closed, and the apparent gain equals the mass of oxygen that entered. State the conservation law as 'atoms are rearranged, none created', which forces the missing reactant to be named.
When explaining why a plant wilts on a hot day, the student says the plant 'breathes out water' or confuses transpiration with respiration, and cannot say which surface the water leaves through.
Both processes involve gas exchange through leaves and both are taught in the same unit, so the labels become interchangeable. Students also lack a clear picture of the water path from root hair to leaf, so they cannot attach the loss of water to a specific structure.
What to do instead
Build a labelled flow diagram once: root hair → xylem → leaf vein → mesophyll → stoma → air, and write 'transpiration' only on that path. Put respiration on a separate diagram with glucose and oxygen, and require the student to name the structure (stoma) and the driving condition (dry, warm, windy air) in every answer about wilting.
When asked to trace the path of blood through the heart, the student says oxygenated blood enters the right atrium, or claims that arteries always carry oxygenated blood.
The diagram is memorised as a shape with chambers rather than as a circuit, and the student's own body is on the left, so 'right' is mapped from their viewpoint rather than the heart's. The artery/vein rule is learned as a slogan without the defining criterion.
What to do instead
Draw the double circulation as two loops with the heart in the middle, and label the right side as receiving blood from the body (deoxygenated) and the left side as sending blood to the body. Define artery and vein by direction relative to the heart, then test the definition on the pulmonary artery and pulmonary vein so the exception is deliberate rather than forgotten.
When asked why a solar eclipse does not occur every month, the student answers that the Moon's orbit is elliptical, or that the Earth's axis is tilted, rather than that the Moon's orbital plane is inclined to the ecliptic.
Tilt of the Earth's axis is the most recently and most strongly taught fact, so it is retrieved for any question about why an alignment fails. The concept of two planes intersecting at an angle is spatially demanding and is often skipped in revision.
What to do instead
Use a physical model: hold a ring at about 5° to a tabletop and move a small ball around it, showing that the ball passes above or below the table plane except at the two nodes. Have the student state the angle and name the nodes, then explain that an eclipse needs new moon or full moon to coincide with a node.
When asked why a sea breeze blows during the day, the student says 'because the sea is cooler than the land, so wind blows from sea to land' without identifying the pressure difference as the cause, and then reverses the answer at night.
The conclusion is memorised as a direction rather than derived from unequal heating and pressure. Students also mix up which surface heats faster, because water has a high specific heat but the student may reason only about colour or depth.
What to do instead
Force the chain to be written in full each time: land heats faster → air over land expands and rises → pressure over land falls → air moves from the higher-pressure sea towards the land. Then run the same chain for night with the roles swapped. Require the word 'pressure' in the answer and check that the direction follows from the stated pressure difference.