BCS Written General Science & Tech cheat sheet

Newton's second law: F = ma; weight is W = mg, distinct from mass, which is invariant with location.

Kinetic energy KE = ½mv²; gravitational potential energy near Earth's surface PE = mgh; total mechanical energy is conserved absent friction.

Ohm's law V = IR; electrical power P = VI = I²R = V²/R; series resistances add, parallel conductances add.

Wave relation v = fλ; for light in vacuum c ≈ 3.0 × 10⁸ m/s; frequency is fixed by source, wavelength changes with medium.

Atomic number Z equals protons and fixes the element; mass number A = protons + neutrons; isotopes differ in neutrons only.

Mole concept: 1 mol = 6.022 × 10²³ particles; molar mass in g/mol numerically equals relative molecular mass.

pH = −log₁₀[H⁺]; pH below 7 is acidic, above 7 basic at 25 °C; strong acid fully dissociates, weak acid partially.

Balancing rule: atoms of each element and total charge must be equal on both sides; oxidation states track electron transfer in redox.

Cell theory: all living things are made of cells, cells arise from pre-existing cells, and the cell is the basic unit of life.

Prokaryotes lack a membrane-bound nucleus and organelles; eukaryotes have a nucleus, mitochondria, and (in plants) chloroplasts.

Photosynthesis: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂, occurring in chloroplast thylakoids (light reactions) and stroma (Calvin cycle).

Cellular respiration: glycolysis in cytoplasm, Krebs cycle in mitochondrial matrix, oxidative phosphorylation on inner mitochondrial membrane.

DNA is a double helix with antiparallel strands; base pairing is A–T and G–C, with G–C pairs joined by three hydrogen bonds.

Mendelian ratios: monohybrid cross of heterozygotes gives 3:1 phenotype and 1:2:1 genotype; dihybrid gives 9:3:3:1 if unlinked.

Taxonomy hierarchy: domain, kingdom, phylum, class, order, family, genus, species; binomial names italicise genus and species.

Enzymes are biological catalysts lowering activation energy; activity is affected by temperature, pH, substrate concentration, and inhibitors.

Incidence counts new cases per population at risk per time; prevalence counts all existing cases at a point or period.

Herd immunity threshold ≈ 1 − 1/R₀; measles with R₀ near 12–18 requires roughly 92–95% coverage to interrupt transmission.

Attack rate = (new cases ÷ population at risk) × 100; case fatality rate = deaths ÷ diagnosed cases × 100.

Sensitivity = true positives ÷ all diseased; specificity = true negatives ÷ all healthy; a test's predictive value depends on prevalence.

Primary prevention reduces exposure before disease; secondary is early detection (screening); tertiary limits disability and complications.

Epidemiological triad: agent, host, environment; vector-borne disease control targets the vector's breeding and biting cycle.

Waterborne diseases include cholera and typhoid; oral rehydration salts treat dehydration from diarrhoeal disease by replacing water and electrolytes.

Vaccines may be live-attenuated (strong, durable response, avoided in immunocompromised) or inactivated/subunit (safer, often need boosters).

1 byte = 8 bits; 1 KiB = 1024 bytes, 1 MiB = 1024 KiB; storage vendors often use decimal prefixes (1 GB = 10⁹ bytes).

Binary to decimal: sum positional powers of 2; hexadecimal groups 4 bits per digit, so one byte is two hex digits.

CPU cycle: fetch, decode, execute, write-back; clock speed in Hz bounds instruction rate, while cores allow parallel threads.

RAM is volatile working memory; ROM is non-volatile; cache (L1/L2/L3) sits between CPU and RAM to reduce latency.

OS roles: process scheduling, memory management, file systems, device drivers, and access control; virtual memory uses disk as an extension of RAM.

Relational databases store rows in tables keyed by primary keys; SQL SELECT–FROM–WHERE–GROUP BY–HAVING–ORDER BY defines logical evaluation order.

Network layers (TCP/IP): link, internet (IP addressing and routing), transport (TCP reliable, UDP unreliable), application (HTTP, DNS, SMTP).

Symmetric encryption uses one shared key (fast, e.g., AES); asymmetric uses a public/private pair (e.g., RSA) and commonly exchanges symmetric keys.

Stress = force ÷ cross-sectional area; strain = change in length ÷ original length; Young's modulus = stress ÷ strain in the elastic region.

A lever balances when effort × effort arm = load × load arm; mechanical advantage = load ÷ effort.

Efficiency = useful output energy ÷ input energy × 100; losses appear as heat, noise, or friction.

Thermodynamics: first law ΔU = Q − W; second law states entropy of an isolated system never decreases, limiting heat-engine efficiency.

Carnot efficiency = 1 − T_cold/T_hot with absolute temperatures in kelvin; no real engine between the same reservoirs exceeds it.

Electrical transmission uses high voltage to reduce current, since power loss in lines is I²R for a fixed delivered power.

Beam bending depends on the second moment of area and material modulus; trusses carry load mainly as axial tension or compression.

Concrete is strong in compression but weak in tension; steel reinforcement carries tensile stress in reinforced concrete.

Machine learning splits data into training, validation, and test sets; a model that fits training noise but fails on test data is overfitted.

Supervised learning uses labelled data; unsupervised finds structure in unlabelled data; reinforcement learning optimises reward through trial and error.

Neural network training adjusts weights by gradient descent on a loss function, with backpropagation computing gradients via the chain rule.

CRISPR-Cas9 uses a guide RNA to target a DNA sequence and the Cas9 nuclease to cut it, enabling gene knockout or repair.

mRNA vaccines deliver a transient genetic message for antigen production; they do not alter the recipient's genome.

Blockchain is an append-only distributed ledger where blocks are linked by cryptographic hashes and consensus replaces a central authority.

Renewable capacity is rated in watts peak; capacity factor = actual energy generated ÷ maximum possible over the period.

5G uses higher-frequency bands and massive MIMO to raise throughput and cut latency, but higher frequencies shorten range and penetrate obstacles poorly.

A hypothesis must be testable and falsifiable; a claim that cannot be contradicted by any observation is outside empirical science.

Independent variable is manipulated; dependent variable is measured; controlled variables are held constant to isolate the effect.

A control group receives no treatment or a placebo so that the effect of the intervention can be separated from other influences.

Randomisation reduces selection bias; blinding (single or double) reduces expectation and measurement bias.

Correlation does not establish causation; criteria include temporal order, dose–response, consistency, and a plausible mechanism.

p-value is the probability of data at least as extreme assuming the null hypothesis is true; it is not the probability the null is true.

Confidence interval estimates a range for a population parameter; a 95% interval comes from a procedure correct in 95% of repeated samples.

Peer review and independent replication are the main filters separating reliable findings from preliminary or spurious results.

Greenhouse gases trap outgoing infrared radiation; CO₂, methane, and nitrous oxide differ in potency and atmospheric lifetime.

Carbon footprint = activity level × emission factor; national inventories are reported as CO₂-equivalent using global warming potentials.

Eutrophication follows nutrient (nitrogen, phosphorus) enrichment, causing algal blooms and oxygen depletion in water bodies.

The waste hierarchy ranks prevention, reuse, recycling, recovery, then disposal; incineration without energy recovery sits near the bottom.

Biodiversity is measured at genetic, species, and ecosystem levels; habitat loss is the leading driver of species decline.

Environmental Impact Assessment screens a project, scopes impacts, predicts effects, and requires mitigation and monitoring before approval.

The precautionary principle permits action under scientific uncertainty where harm could be serious or irreversible.

Polluter-pays and sustainable-development principles integrate environmental cost into economic decisions; EIA and permits are common policy instruments.