Miyagi Entrance Science common mistakes
Miyagi Entrance Science · Understand the traps and how to avoid them.
When asked to find the image of a point or object in a plane mirror, the candidate draws the image on the mirror surface itself, or places it at the same distance in front of the mirror as the object, instead of drawing a perpendicular from the object through the mirror and marking the image the same distance behind it.
The everyday phrase 'reflection in the mirror' suggests the image sits on the glass, and candidates memorize 'the image is the same distance away' without anchoring the distance on the correct side of the mirror line. They also skip the perpendicular construction and just eyeball a symmetric-looking position.
What to do instead
Always draw the mirror as a line, drop a perpendicular from each key point of the object to the mirror line, extend it beyond the line, and mark the image point at the measured equal distance on the far side. Check with a ray: a ray from the object hitting the mirror at 90 degrees must return along itself, and the line from the image to the eye must pass through the mirror at the reflection point. Do three practice constructions (point, arrow, letter) and verify with a ruler each time.
For a convex lens the candidate treats every object position as producing a real, inverted image, and cannot state where the object must be for a magnified virtual image (the magnifying-glass case). They also place the focal point at the centre of the lens or confuse focal length with image distance.
Textbook ray diagrams are usually drawn for one standard case (object beyond 2f), so candidates generalize that diagram to all positions. The virtual-image case requires extending refracted rays backwards, which is visually counterintuitive and is often skipped in revision.
What to do instead
Build a table of the five object positions (beyond 2f, at 2f, between f and 2f, at f, inside f) with the image type, orientation, size and use (camera, projector, magnifier). For each, draw the three standard rays: parallel-to-axis then through F, through the centre undeviated, and through F then parallel to axis. For the inside-f case, dash the backward extensions and label the image 'virtual'. Rehearse the rule 'object inside f gives virtual, upright, magnified'.
When a question describes a moving object, the candidate computes distance as speed multiplied by time but then adds or subtracts speeds incorrectly in relative-motion situations, or treats a distance-time graph's slope as speed without checking the axes, and reports an average speed by averaging two speeds rather than dividing total distance by total time.
Candidates memorize the formula triangle d = v t but never practise the two-part journey where the same distance is covered at different speeds. Averaging the two speeds feels natural and is arithmetically easy, so the error survives self-checking.
What to do instead
For any multi-stage journey, write a table with columns for each stage (distance, time, speed) and one total row, then compute average speed as total distance divided by total time. Practise a worked example: 6 km at 4 km/h then 6 km at 12 km/h gives 12 km in 3 h, so 4 km/h, not 8 km/h. For graphs, always write the axis quantities and units at the top of your working before reading a gradient.
In circuit problems the candidate applies the same current to every branch of a parallel circuit, or applies the same voltage across each resistor in a series circuit, and adds resistances in parallel by simple addition.
The series rules are learned first and are simpler, so they get over-applied. Candidates also memorize 'current is used up' from everyday language about batteries, which conflicts with the conservation of current at a junction.
What to do instead
Before calculating, label the circuit as series or parallel and write the matching rule set: series has one current everywhere and voltages that add; parallel has one voltage across every branch and currents that add at junctions. Use the reciprocal rule 1/R = 1/R1 + 1/R2 and sanity-check that a parallel combination is smaller than the smallest resistor. State explicitly that current is not consumed; it is the energy that is transferred.
The candidate writes a word equation for a reaction but then balances it by changing subscripts (turning H2O into H2O2, or CO2 into CO) instead of placing coefficients in front of the formulae, and omits state symbols or the conditions written above the arrow.
Balancing is taught as 'make the numbers match', and changing a subscript is the fastest way to make them match. Candidates also do not yet see formulae as fixed identities of substances, so they treat them as adjustable labels.
What to do instead
Adopt a hard rule: subscripts in a formula are never edited; only coefficients may change. Balance by counting each element on both sides in a table, starting with elements that appear in only one compound on each side, and leave hydrogen and oxygen until last. Then verify every element again. Write state symbols and conditions (heat, catalyst) as part of the equation, since exam mark schemes often award them separately.
When asked to identify an unknown solution, the candidate names a reagent and says it 'will react' without stating the observable change (colour of precipitate, gas evolved, smell, colour change of indicator), and confuses the limewater test for carbon dioxide with the glowing-splint test for oxygen.
Candidates learn the reagent names as a list and treat the observation as obvious. Practical work is often watched rather than performed, so the link between a test and its visible result is weak.
What to do instead
Build a two-column test table: 'test' and 'positive observation'. Include: limewater turns milky for CO2; glowing splint relights for oxygen; burning splint gives a squeaky pop for hydrogen; damp red litmus turns blue for ammonia; silver nitrate gives a white precipitate with chloride and a yellow one with iodide; barium chloride gives a white precipitate with sulfate. For each unknown, write the observation first, then the conclusion, in that order.
The candidate describes ion formation as atoms 'gaining or losing protons' to become charged, and writes the formula of an ionic compound without balancing the charges, for example writing MgCl or AlO instead of MgCl2 and Al2O3.
The words 'positive' and 'negative' are associated with protons and electrons loosely, and the rule that the nucleus is fixed is stated once and then forgotten. Charge balancing is a separate skill from writing symbols and is rarely drilled to automaticity.
What to do instead
State the invariant aloud each time: only electrons move; the proton number, and therefore the element, never changes. Metal atoms lose electrons to form positive ions; non-metal atoms gain electrons to form negative ions. Then write ionic formulae by the crossover method: write the ion charges above the symbols and swap the magnitudes as subscripts, cancelling to the simplest ratio. Check that the total positive charge equals the total negative charge.
When explaining a food chain or energy flow, the candidate draws arrows pointing from the predator to the prey (or uses 'eaten by' arrows), and states that energy is lost because organisms 'use it up' without naming respiration, heat, or undigested material, and treats decomposers as outside the ecosystem.
Everyday phrasing 'the fox eats the rabbit' puts the fox first, so the arrow direction follows the sentence order. The loss of energy is described vaguely because the fate of assimilated energy is not linked to cellular respiration in the candidate's mind.
What to do instead
Fix the convention: the arrow points in the direction the energy flows, from the organism being eaten to the eater, and read it as 'is eaten by'. For energy loss, always give the mechanism: respiration releases energy as heat, some material is undigested and egested, and some is lost in excretion. Draw a pyramid of energy or biomass and label each transfer as roughly one tenth. Include decomposers as recyclers of nutrients, not as an energy source for the top predator.
The candidate confuses mitosis and meiosis: saying meiosis produces identical body cells for growth, or that mitosis halves the chromosome number, and cannot state what happens to chromosome number at fertilisation and in the gametes.
Both are 'cell division', and the two names look and sound alike. The purpose of each process is memorized separately from its outcome, so the two sets of facts get swapped under time pressure.
What to do instead
Anchor each process to its purpose: mitosis makes genetically identical cells with the same chromosome number for growth and repair; meiosis makes gametes with half the chromosome number and creates genetic variation by independent assortment and crossing over. Write the sequence for a human: body cell 46, gamete 23, zygote 46. Draw a simple diagram for each and label chromosome number before and after, then test yourself by explaining why a species would be in trouble if gametes were made by mitosis.
The candidate explains day and night, the seasons, or the phases of the Moon by saying the Earth moves closer to and further from the Sun, or that the Earth's distance changes cause the seasons, and confuses the Moon's rotation with its revolution when explaining why we always see the same face.
Diagrams in textbooks are drawn to scale-free ellipses and the tilt is easy to overlook, so distance becomes the intuitive cause. The Moon's synchronous rotation is a single fact often memorized without the mechanism.
What to do instead
State the causes explicitly: day and night come from the Earth's rotation on its axis; the seasons come from the constant 23.4-degree tilt of the axis combined with revolution, which changes the angle of sunlight and day length, not the distance. For the Moon, note that its rotation period equals its revolution period (about 27.3 days), so the same hemisphere always faces Earth. Sketch the orbit with the tilt drawn and label the Northern Hemisphere's summer solstice position to confirm the sunlight angle.