Yamanashi Entrance Science common mistakes
Yamanashi Entrance Science · Understand the traps and how to avoid them.
In mechanics problems involving a rough surface or a pulley, the candidate writes the equation of motion without drawing a free-body diagram, then leaves out one force (often the normal force on an inclined plane or the tension in one part of the string) and obtains an acceleration that is wrong by a factor such as g sinθ instead of the correct combination of forces.
Under time pressure, candidates jump straight to the formula they memorised (F = ma, or a = g sinθ) and treat it as a template, so they never enumerate the forces actually acting. Inclined planes and connected bodies look familiar, so the brain recognises the pattern and skips the analysis step where the missing force would have been noticed.
What to do instead
Before writing any equation, draw the object as a dot and draw every force as an arrow with a label (gravity, normal, friction, tension). Then choose axes along and perpendicular to the motion, and write ΣF = ma separately for each axis. Check the perpendicular direction first: on an incline it gives N = mg cosθ, which then fixes the friction magnitude. Do this on at least five incline and pulley problems until the diagram is automatic.
In electromagnetism, the candidate applies the right-hand rule for a current-carrying wire or a moving charge but reverses the direction of the magnetic force, or confuses the direction of the induced current with the direction of the magnetic field it produces (Lenz's law), so a question asking which way the current flows in a coil gets the sign wrong.
There are several right-hand rules (force on a current, field around a wire, induced current) that look similar, and candidates memorise one gesture and reuse it for all three. The physical meaning of Lenz's law - the induced current opposes the change in flux - is understood only verbally, so it cannot be applied to a concrete geometry under exam conditions.
What to do instead
Write out each rule as a sentence before using it: F = I L × B (force is perpendicular to both the current and the field); the field lines around a straight wire circle it in the direction the fingers curl when the thumb points along the current; the induced current produces a field that opposes the change in flux. For Lenz's law, always state explicitly whether the flux through the coil is increasing or decreasing and which direction the external field points, then choose the current that opposes that change. Practise on a coil entering and leaving a magnetic region.
In wave problems, the candidate reads a displacement–position graph and a displacement–time graph as if they were interchangeable, taking the wavelength from the time axis or the period from the position axis, and then computes v = fλ with a mixed pair of values.
Both graphs look like a sine curve, and candidates match on shape rather than on axis labels. The distinction between a snapshot of the wave at one instant and the history of one point is a conceptual point that is easy to nod at and hard to apply when the axes are not labelled in words.
What to do instead
Before reading any value off a wave graph, say aloud what the horizontal axis measures. If it is position, the spacing between crests is λ; if it is time, the spacing is T. Then write v = λ/T = fλ with the units attached so a mismatch is visible. Also practise the direction-of-motion question: on a snapshot graph, a point on the leading slope moves opposite to the wave direction; check this against a slightly later snapshot.
In thermodynamics, the candidate uses the first law as ΔU = Q + W without fixing a sign convention, so work done by the gas and work done on the gas are mixed within one solution, and an isothermal expansion is treated as if no heat were exchanged.
Textbooks differ on whether W means work done by or on the system, and candidates carry a memorised formula from one source into a problem written with the other convention. The isothermal case is confused with the adiabatic case because both are drawn as smooth curves on a p–V diagram and the words sound similar.
What to do instead
At the top of every thermodynamics answer, write the convention you are using, e.g. ΔU = Q − W_by the gas. Then identify the process by name and state its constraints: isothermal means T constant so ΔU = 0 and Q = W; adiabatic means Q = 0 so ΔU = −W; isochoric means W = 0 so ΔU = Q. Work through one example of each on a p–V diagram and shade the area that represents the work.
In stoichiometry and gas problems, the candidate balances the equation by adjusting subscripts rather than coefficients, or uses the limiting reagent without checking it, and reports a product mass based on the reactant that happens to be listed first.
Balancing by changing subscripts is a habit left over from arithmetic practice, and it produces an equation that looks balanced while describing a different substance. The limiting-reagent check is a separate step that feels like extra work, so it is skipped when the numbers look convenient.
What to do instead
Balance only by writing coefficients in front of formulas and never touch a subscript; after balancing, count each element on both sides as a check. For limiting reagent, convert every reactant amount to moles, divide each by its coefficient in the balanced equation, and identify the smallest quotient as limiting. Do this explicitly even when one reactant is obviously in excess, and state the limiting reagent in the answer.
In inorganic chemistry, the candidate predicts the products of a reaction between an acid and a base or a metal and an acid from memory of a similar-looking reaction, without checking solubility rules or the reactivity series, and so writes an insoluble product as aqueous or predicts a reaction that does not occur.
Reaction prediction is often taught as a set of examples rather than a decision procedure, so candidates pattern-match on the formulas. Solubility rules and the reactivity series are memorised as lists but not applied as gates before writing products.
What to do instead
Use a fixed sequence: identify the reaction type (neutralisation, precipitation, redox, gas evolution), apply the relevant rule (solubility table for precipitation; reactivity series for displacement; strong/weak acid for neutralisation), then write the products and balance. Mark every precipitate with its state symbol. Practise by classifying ten reactions before writing any products, then checking each against the rules.
In organic chemistry, the candidate draws a structural formula that omits a hydrogen or gives carbon five bonds, or names a compound without identifying the longest carbon chain containing the principal functional group, and so produces a name that does not match the structure drawn.
Skeletal and condensed formulas are read quickly, and hydrogens on carbon are invisible in the skeletal form, so the valence count is not verified. Naming is done by scanning from the end that looks convenient rather than by applying the priority rules for the principal functional group.
What to do instead
After drawing any structure, count bonds on every carbon and write the H count explicitly. For naming, follow the order: find the longest chain containing the principal group, number from the end that gives that group the lowest locator, then list substituents alphabetically. Work in both directions - name to structure and structure to name - on the same molecule and check they agree.
In genetics, the candidate treats a cross as a single calculation and does not separate the inheritance pattern (autosomal, sex-linked, dominant, recessive) from the probability calculation, so a sex-linked trait is analysed as if both sexes had the same genotype possibilities, or the candidate forgets that a recessive phenotype requires two recessive alleles.
Punnett squares are practised heavily as a mechanical exercise, which encourages applying one template to every problem. The step of reading the pedigree or the wording to determine the mode of inheritance is compressed or skipped.
What to do instead
Before drawing a Punnett square, write down the mode of inheritance and the genotypes of the parents, including sex chromosomes where relevant. Then state the gametes each parent can produce, fill the square, and count phenotypes by sex separately if the trait is sex-linked. Check that the sum of phenotype ratios equals the total number of offspring combinations.
In ecology and evolution questions, the candidate explains a change in a population as if individual organisms adapted during their lifetime, or describes natural selection as a directed response to need, rather than as differential survival and reproduction of pre-existing variation.
Everyday language uses 'adapt' for both individual adjustment and evolutionary change, and the Lamarckian phrasing is intuitive. The distinction between variation existing before selection and variation arising in response to a need is a conceptual point that is easy to state and easy to lose under time pressure.
What to do instead
Write the mechanism as a four-step chain every time: (1) individuals in the population vary; (2) the variation is heritable; (3) some variants leave more offspring in the current environment; (4) allele frequencies change over generations. If a question asks about a single organism's response, answer with acclimatisation or behaviour, not evolution. Check your answer contains the words 'variation', 'heritable', and 'differential reproduction'.
In Earth science and in data-analysis questions, the candidate reads a graph or table by picking the value at the leftmost or rightmost point instead of the requested point, ignores the units on the axes, or fits a straight line through clearly curved data and reports a gradient as if the relationship were linear.
Graph-reading is assumed to be a basic skill and is rarely practised explicitly, so candidates scan for a number that looks plausible. Units are treated as decoration, and the shape of the data is not checked before a line is drawn.
What to do instead
Read every graph in a fixed order: axis labels and units, then the range, then the shape (linear, curved, saturating), then the specific point asked for. When a gradient is requested, check linearity first; if the data curve, say so and compute a local gradient or transform the axis. For Earth science, always convert to SI units and state the direction (e.g. north-east) alongside the magnitude.