Sri Lanka Scientific Service Exam cheat sheet

SI base units: length metre (m), mass kilogram (kg), time second (s), electric current ampere (A), thermodynamic temperature kelvin (K), amount of substance mole (mol), luminous intensity candela (cd).

Newton's second law: F = ma; weight W = mg where g ≈ 9.81 m/s² near Earth's surface.

Work done by a constant force: W = F d cos θ; kinetic energy KE = ½mv²; gravitational potential energy PE = mgh.

Ohm's law: V = IR; electrical power P = VI = I²R = V²/R.

Ideal gas law: PV = nRT; at STP (0 °C, 1 atm) one mole of ideal gas occupies 22.4 L.

pH = −log₁₀[H⁺]; a change of one pH unit corresponds to a tenfold change in hydrogen ion concentration.

Percent error = (|experimental − accepted| / accepted) × 100%; percent difference = (|a − b| / ((a + b)/2)) × 100%.

Dimensional analysis: both sides of a valid physical equation must have identical base dimensions; use it to check equations and convert units.

Cell theory: all living organisms are composed of one or more cells; the cell is the basic unit of life; all cells arise from pre-existing cells.

DNA base pairing: adenine pairs with thymine (two hydrogen bonds), guanine pairs with cytosine (three hydrogen bonds).

Michaelis–Menten equation: v = Vmax[S]/(Km + [S]); Km is the substrate concentration at which v = ½Vmax.

Hardy–Weinberg equilibrium: p² + 2pq + q² = 1, where p and q are allele frequencies and p + q = 1.

Periodic trends: atomic radius decreases across a period and increases down a group; electronegativity increases across a period and decreases down a group.

First law of thermodynamics: ΔU = Q − W; for an isolated system ΔU = 0.

Reaction rate law: rate = k[A]^m[B]^n; overall order = m + n; for a first-order reaction half-life t½ = ln2/k ≈ 0.693/k.

Central dogma of molecular biology: DNA → RNA → protein (replication, transcription, translation).

Null hypothesis (H₀) states no effect or no difference; the alternative hypothesis (H₁) states the effect or difference being tested.

Type I error: rejecting a true null hypothesis (false positive, probability α); Type II error: failing to reject a false null hypothesis (false negative, probability β). Power = 1 − β.

p-value: probability of observing a result at least as extreme as the data, assuming H₀ is true; reject H₀ when p < α.

Parametric tests (t-test, ANOVA) assume normality and homogeneity of variance; non-parametric alternatives include Mann–Whitney U and Kruskal–Wallis tests.

Pearson correlation coefficient r ranges from −1 to +1; r measures linear association, not causation.

Standard error of the mean: SEM = s/√n; 95% confidence interval for a mean ≈ x̄ ± 1.96 × SEM for large n.

Randomisation reduces selection bias; blinding (single or double) reduces observer and measurement bias; a control group provides a baseline for comparison.

Sensitivity = true positives / (true positives + false negatives); specificity = true negatives / (true negatives + false positives).

Informed consent requires disclosure of purpose, procedures, risks, benefits, alternatives, and the right to withdraw without penalty.

Research ethics review boards (IRBs/ERCs) approve protocols involving human participants before data collection begins.

Authorship requires substantial contribution to conception, design, execution, or interpretation, plus drafting or critical revision and final approval.

Plagiarism is the unattributed use of another's ideas, words, or data; self-plagiarism reuses one's own published work without citation.

Conflict of interest must be disclosed in grant applications, publications, and peer review; undisclosed conflicts undermine scientific integrity.

Data fabrication (inventing data) and falsification (altering or selectively reporting data) are serious research misconduct.

Good laboratory practice (GLP) requires standard operating procedures, calibration records, and traceable raw data.

Peer review is confidential; reviewers must decline if they have a conflict and must not use unpublished manuscript content.