SITEEE common mistakes
SITEEE · Understand the traps and how to avoid them.
Reaches for a constant-acceleration formula (v = u + at, v² = u² + 2as) on any question that mentions speed or time, even when the net force varies - a block attached to a spring, a body falling with air resistance, or a charged particle in a non-uniform field.
School coaching drills the SUVAT equations until they become the default response to 'find the velocity', and the condition that acceleration must be constant is never used as an explicit checkpoint.
What to do instead
Write the net-force expression before choosing any formula. If the force depends on position or velocity, use work–energy or integrate a = dv/dt; use SUVAT only after you have shown the acceleration is constant over the whole interval.
Switches sign conventions inside a single optics or thermodynamics question - applying Cartesian signs to a mirror and then treating a virtual image distance as positive, or writing ΔU = Q − W and then substituting work done on the gas as positive.
Different textbooks set out different conventions, so candidates memorise the formulas but never fix the convention the formula belongs to.
What to do instead
Write your convention in one line at the top of the rough sheet (e.g. 'distances measured from pole, along incident light positive') and convert every given quantity into it before substituting.
Substitutes grams where kilograms are needed in F = ma, or mixes centimetres and metres inside a moment-of-inertia, pressure or density calculation, so the answer is wrong by a power of ten.
Numbers are read faster than units at roughly one minute per question, and Indian textbooks freely mix g/cm³, dyne and cm in worked examples.
What to do instead
Convert every given value to SI on a single first line before touching a formula, and carry the units through the algebra so a stray power of ten becomes visible.
Calculates the amount of product from whichever reactant has more moles or the larger mass, instead of testing which reactant is limiting.
Limiting-reagent problems in practice sets usually hand you the limiting species already, so the division-by-coefficient step is never rehearsed.
What to do instead
Balance the equation, divide the moles of each reactant by its stoichiometric coefficient, and take the smallest quotient as the limiting reagent; every product calculation then starts from that reactant.
States that adding a catalyst, or adding an inert gas at constant volume, shifts an equilibrium towards the products.
Le Chatelier's principle is memorised as the slogan 'a change shifts the equilibrium', and a catalyst is associated in the candidate's mind with speeding up the forward reaction.
What to do instead
Anchor on what each change actually alters: a catalyst only shortens the time to reach the same equilibrium position, and an inert gas at constant volume changes no partial pressure. Only changes in concentration, partial pressure, volume or temperature move the position.
Applies [H⁺] = √(Ka·C) to every weak acid, including very dilute solutions, mixtures of two acids, and buffer systems.
One formula is retained from the ionic-equilibrium chapter and its validity condition (small degree of dissociation) is never mentioned.
What to do instead
Test the approximation first: if C/Ka is not large or dissociation exceeds about five per cent, solve the quadratic from an ICE table; for a buffer, switch to Henderson–Hasselbalch.
Divides both sides of a trigonometric or polynomial equation by sin x, cos x or x to simplify, silently discarding every solution where that factor equals zero.
Cancelling feels like progress, and once the factor is gone nothing in the working signals that solutions were lost.
What to do instead
Factor, never divide. Move everything to one side, factor out the common expression, and set each factor to zero separately, including the factor you were tempted to cancel.
Squares both sides, cross-multiplies or takes logarithms and then accepts every resulting root without checking domain restrictions such as log argument > 0, denominator ≠ 0, or the principal range of an inverse trigonometric function.
Squaring and cross-multiplication are taught as safe algebraic moves, and once a numerical answer appears the candidate moves on rather than verifying it.
What to do instead
Budget ten seconds to substitute each candidate back into the original equation and its domain restrictions, and explicitly strike out the roots that fail.
Quotes the 9:3:3:1 dihybrid F2 ratio for a test cross or a linked-gene cross, or reports a 1:2:1 ratio as the phenotypic ratio.
Ratios are stored as strings attached to the phrase 'dihybrid cross' instead of being derived from the cross actually described in the stem.
What to do instead
Write the parental genotypes and their gametes, build the Punnett square, then read off the ratio and label it as genotypic or phenotypic before matching an option.
Places crossing over in prophase II, or claims that meiosis produces four genetically identical daughter cells.
Meiosis I and II are memorised as parallel stage lists modelled on mitosis, and the two divisions blur together under time pressure.
What to do instead
Anchor on outcomes rather than stage names: meiosis I separates homologous chromosomes (2n to n, with crossing over in prophase I) and meiosis II separates sister chromatids, giving four genetically distinct haploid cells.