GCE A/L Science for Technology flashcards

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

Newton (unit)

The SI unit of force, defined as the force that gives a 1 kg mass an acceleration of 1 m·s⁻². In base units it equals kg·m·s⁻².

Systematic error

An error that shifts every reading in the same direction by a constant or proportional amount, caused by faulty calibration or instrument bias, and removable only by correction or recalibration.

Dimensional analysis

A method of checking equations by comparing the base-unit dimensions of each side. Both sides must match, and it also predicts the form of a relationship up to a dimensionless constant.

Relative uncertainty

The absolute uncertainty of a measurement divided by its value. For products and quotients the relative uncertainties of the factors add to give the result's relative uncertainty.

Archimedes' principle

A body wholly or partly immersed in a fluid experiences an upthrust equal to the weight of the fluid it displaces. This explains floating and apparent loss in weight.

Young's modulus

Tensile stress divided by tensile strain in the linear region of a stress–strain curve. It measures a material's stiffness and is independent of specimen dimensions.

Conservation of momentum

In a closed system with no external resultant force, the total momentum before an interaction equals the total after. It applies to elastic and inelastic collisions alike.

Centripetal acceleration

The acceleration of a body moving in a circle, directed towards the centre and equal to v²/r or ω²r. It changes direction, not speed, of motion.

Specific latent heat

The thermal energy needed to change the state of 1 kg of a substance at constant temperature, without changing its temperature. It is fusion for melting and vaporisation for boiling.

First law of thermodynamics

Energy conservation for a gas: the heat supplied equals the increase in internal energy plus the work done by the gas. For an isothermal change internal energy is unchanged.

Ideal gas equation

pV = nRT relates pressure, volume, amount and absolute temperature of an ideal gas, with R approximately 8.31 J·mol⁻¹·K⁻¹. Temperature must be in kelvin.

Carnot efficiency

The maximum possible efficiency of a heat engine operating between hot and cold reservoirs, equal to 1 − T_cold/T_hot with both temperatures in kelvin.

Total internal reflection

When light travels from a denser to a rarer medium at an angle greater than the critical angle, it is completely reflected back. The critical angle satisfies sin C = n₂/n₁.

Snell's law

The law of refraction: n₁ sin θ₁ = n₂ sin θ₂, where each n is the refractive index and each angle is measured from the normal at the interface.

Diffraction grating equation

d sin θ = nλ relates slit spacing d, diffraction angle θ, order n and wavelength λ. Smaller slit spacing spreads the orders further apart.

Decibel scale

A logarithmic measure of sound intensity level: L = 10 log₁₀(I/I₀), with reference intensity I₀ = 1 × 10⁻¹² W·m⁻². Ten decibels mean ten times the intensity.

Kirchhoff's laws

Two circuit rules: the sum of currents entering a junction equals the sum leaving, and the sum of e.m.f.s around a closed loop equals the sum of potential differences.

Faraday's law of induction

The induced e.m.f. in a coil equals the negative rate of change of magnetic flux linkage, −N dΦ/dt. A faster change of flux produces a larger induced e.m.f.

Lenz's law

The direction of an induced current is always such that its magnetic effect opposes the change in flux that produced it, a consequence of energy conservation.

Zener diode

A diode designed to operate in reverse breakdown at a defined voltage, holding that voltage nearly constant. It is used for voltage regulation and reference supplies.

Ionic bonding

Electrostatic attraction between oppositely charged ions formed when a metal transfers electrons to a non-metal. Such compounds are crystalline and conduct only when molten or dissolved.

Mole concept

One mole contains 6.022 × 10²³ particles and has a mass in grams equal to the relative molar mass. Amount in moles equals mass divided by molar mass.

Le Chatelier's principle

When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, it shifts in the direction that opposes the change and restores equilibrium.

Oxidation number

A number assigned to an atom showing its apparent electron gain or loss. An increase indicates oxidation, a decrease indicates reduction, and the sum in a neutral compound is zero.

Addition polymerisation

A reaction in which unsaturated monomers join through their double bonds to form a long chain with no other product. Examples include ethene forming poly(ethene).

Condensation polymerisation

Monomers with two functional groups join with the elimination of a small molecule such as water, forming a polymer chain. Nylon and PET are made this way.

Markovnikov's rule

When a hydrogen halide adds to an unsymmetrical alkene, the hydrogen attaches to the carbon already carrying more hydrogen atoms, giving the major product.

Thermoplastic

A polymer whose chains are held by weak intermolecular forces, so it softens on heating and can be remoulded repeatedly. Poly(ethene) and PVC are examples.

Meiosis

A reduction division producing four haploid daughter cells from one diploid cell, with crossing over and independent assortment generating genetic variation in gametes.

Transcription

The synthesis of messenger RNA from a DNA template by RNA polymerase in the nucleus. The mRNA carries the codon sequence to the ribosome for translation.

Binary fission

Asexual reproduction in bacteria in which the cell replicates its DNA and divides into two identical daughter cells. Under ideal conditions numbers double at a constant rate.

Polymerase chain reaction

A technique that amplifies a DNA segment through repeated cycles of heat denaturation, primer annealing and extension by a thermostable polymerase, doubling the DNA each cycle.

Gear ratio

The number of teeth on the driven gear divided by the number on the driving gear. A larger ratio increases output torque while reducing output speed in the same proportion.