EJU Science flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Newton's second law

Net force equals mass times acceleration. Acceleration points along the net force, and doubling the mass halves the acceleration produced by the same applied force.

Conservation of momentum

If the net external impulse on a system is zero, its total momentum stays constant. This applies to every collision, elastic or inelastic, and to explosions.

Coefficient of restitution

Ratio of relative separation speed to relative approach speed for two colliding bodies. It equals one for a perfectly elastic collision and zero when the bodies stick together.

Uniform circular motion

Motion on a circle at constant speed, with acceleration v squared divided by r directed toward the centre. Period equals two pi r over v, and angular velocity is v over r.

Mechanical energy conservation

When only conservative forces do work, kinetic plus potential energy is constant. Gravitational potential near Earth is mass times g times height; spring potential is half k x squared.

Ideal gas law

Pressure times volume equals moles times the gas constant times absolute temperature. Temperature must be in kelvin and the constant is 8.31 joules per mole kelvin.

First law of thermodynamics

The change in internal energy equals heat added to the gas plus work done on the gas. Internal energy change depends only on the initial and final states.

Coulomb's law

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation, acting along the joining line.

Snell's law

At an interface, the refractive index of the first medium times the sine of the incidence angle equals the same product for the second medium; angles are measured from the normal.

Photoelectric effect

Light above a threshold frequency ejects electrons from a metal. Maximum kinetic energy equals photon energy minus the work function, so brighter light adds electrons but not their maximum speed.

Faraday's law of induction

A changing magnetic flux through a circuit induces an electromotive force equal to the rate of change of flux, with the induced current opposing the change by Lenz's law.

Mole

One mole contains 6.02 times ten to the twenty-third particles and has a mass in grams numerically equal to the molar mass. Moles equal mass divided by molar mass.

Molar volume of gas

One mole of any ideal gas occupies 22.4 litres at zero degrees Celsius and one atmosphere. At 25 degrees Celsius and one atmosphere the volume is about 24.5 litres.

Molarity

Moles of solute per litre of solution. During dilution the amount of solute is unchanged, so the initial concentration times initial volume equals final concentration times final volume.

pH

The negative logarithm of the hydronium ion concentration. A strong acid dissociates completely, while a weak acid dissociates only partly and so gives a higher pH at equal concentration.

Buffer solution

A weak acid mixed with its conjugate base, or a weak base with its conjugate acid, that resists pH change on adding small amounts of acid or base; pH follows the Henderson–Hasselbalch relation.

Le Châtelier's principle

When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, it shifts in the direction that counteracts the disturbance. A catalyst changes rate but not position.

Equilibrium constant

Product concentrations raised to their stoichiometric coefficients divided by the same expression for reactants, measured at equilibrium. Its value depends on temperature and not on initial amounts.

Faraday's law of electrolysis

The amount of substance deposited or dissolved at an electrode is proportional to the charge passed. Charge equals current times time, and one mole of electrons carries 96,500 coulombs.

Standard electrode potential

Cell electromotive force equals the cathode potential minus the anode potential under standard conditions. A positive value means the cell reaction is spontaneous and relates to free energy by minus nFE.

Esterification

A carboxylic acid and an alcohol react, with a small amount of strong acid as catalyst, to give an ester and water. The reaction is slow and reversible.

Addition reaction

Alkenes and alkynes add hydrogen, halogens or hydrogen halides across the multiple bond, turning unsaturated compounds into saturated or less unsaturated products without losing any atoms.

Prokaryotic cell

A cell with no nucleus and no membrane-bound organelles, whose DNA lies in a nucleoid. Bacteria are prokaryotes and possess ribosomes but no mitochondria, chloroplasts or nuclear envelope.

Mitochondrion

Organelle bounded by a double membrane whose inner membrane folds into cristae. It runs the electron transport chain and oxidative phosphorylation, supplying most of the ATP a eukaryotic cell uses.

Chloroplast

Plant organelle containing thylakoids stacked into grana. Light reactions occur in the thylakoid membranes, while the Calvin cycle fixes carbon dioxide in the surrounding stroma.

Mitosis

Nuclear division that produces two genetically identical daughter cells with the same chromosome number. It follows DNA replication in S phase and supports growth, repair and asexual reproduction.

Meiosis

Two successive divisions after a single DNA replication, producing four haploid cells. Homologous chromosomes pair in prophase one and crossing over creates new combinations of alleles.

Glycolysis

Breakdown of glucose to pyruvate in the cytosol, giving two ATP and two NADH per glucose without oxygen. It is the first stage of both aerobic and anaerobic respiration.

Law of segregation

An organism carries two alleles for each gene, and these separate during gamete formation so that each gamete receives only one. Fertilisation restores the paired condition in the offspring.

Transcription

RNA polymerase copies one strand of DNA into messenger RNA, which carries the base sequence to a ribosome where codons are translated into a chain of amino acids.

Trophic level

A feeding position in a food chain, defined by the number of energy transfers from producers. Only about ten percent of energy passes to the next level, which limits chain length.

Nitrogen fixation

Conversion of atmospheric nitrogen gas into ammonia by bacteria such as rhizobia in root nodules or by free-living soil bacteria, making nitrogen available for plant proteins and nucleic acids.