Technical Sciences Grade 12 Review

Essential definitions, laws, and vocabulary terms from Grade 12 Technical Sciences NSC examination papers covering mechanics, properties of matter, electricity, optics, organic chemistry, and electrochemistry.

Homologous series

A series of organic compounds that can be described by the same general formula and in which each member differs from the next by a $-\text{CH}_2-$ unit.

Functional group

An atom or group of atoms that forms the centre of chemical activity in a molecule and gives the organic molecule its characteristic chemical properties.

Hydrocarbon

An organic compound consisting solely of hydrogen and carbon atoms.

Saturated hydrocarbon

A hydrocarbon in which all the chemical bonds between carbon atoms are single covalent bonds.

Unsaturated hydrocarbon

A hydrocarbon containing one or more double or triple covalent bonds between carbon atoms.

Polymer

A large molecule composed of many small, repeating structural units (monomers) covalently bonded together.

Melting point

The temperature at which the solid and liquid phases of a substance are in thermodynamic equilibrium.

Boiling point

The temperature at which the vapour pressure of a liquid equals the external atmospheric pressure.

Vapour pressure

The pressure exerted by a vapour in equilibrium with its liquid phase in a closed container.

Electrolyte

A substance that produces an electrically conducting solution containing free ions when dissolved in a solvent or when molten.

Electrolysis

A process wherein electrical energy is converted into chemical energy to drive a non-spontaneous chemical redox reaction.

Galvanic cell

An electrochemical cell that generates electrical energy from a spontaneous chemical redox reaction.

Oxidising agent

A substance that undergoes reduction by accepting electrons, thereby causing another substance to be oxidised.

Reducing agent

A substance that undergoes oxidation by donating electrons, thereby causing another substance to be reduced.

Newton's First Law of Motion

An object will remain at rest or continue to move at a constant velocity in a straight line unless acted upon by a non-zero resultant (net) external force.

Newton's Second Law of Motion

When a net force acts on an object, the object accelerates in the direction of the net force with an acceleration that is directly proportional to the force and inversely proportional to the mass of the object: $\mathbf{F}_{\text{net}} = m\mathbf{a}$.

Newton's Third Law of Motion

When object A exerts a force on object B, object B simultaneously exerts an equal in magnitude and opposite in direction force on object A.

Inertia

The resistance of any physical object to any change in its velocity, including changes to the object's speed or direction of motion.

Isolated system

A system on which the resultant external force acting is zero.

Principle of conservation of linear momentum

The total linear momentum of an isolated system remains constant in both magnitude and direction.

Impulse

The product of the net force acting on an object and the contact time over which the force acts, equal to the change in momentum: $J = F_{\text{net}}\Delta t = \Delta p$.

Elastic collision

A collision in which both total linear momentum and total kinetic energy are conserved.

Inelastic collision

A collision in which total linear momentum is conserved, but total kinetic energy is not conserved.

Mechanical energy

The sum of the gravitational potential energy and kinetic energy of an object: $ME = E_k + E_p$.

Work

The product of the displacement of an object and the component of the applied force parallel to the displacement: $W = F\Delta x\cos(\theta)$.

Elasticity

The property of a body whereby it regains its original shape and size after the removal of a deforming force.

Stress

The internal restoring force per unit cross-sectional area of a material: $\sigma = \frac{F}{A}$.

Strain

The ratio of the change in dimension (such as length) to the original dimension: $\varepsilon = \frac{\Delta L}{L}$.

Hooke's law

The strain produced in an elastic body is directly proportional to the applied stress, provided the elastic limit of the material is not exceeded.

Young's modulus of elasticity

The ratio of tensile or compressive stress to tensile or compressive strain in a material within its proportional limit: $K = \frac{\sigma}{\varepsilon}$.

Viscosity

The internal friction or property of a fluid that represents its resistance to flow.

Pascal's law

Pressure exerted at any point on an enclosed, static, incompressible fluid is transmitted equally and undiminished in all directions throughout the fluid.

Semiconductor

A material whose electrical conductivity lies between that of a conductor and an insulator.

Capacitor

An electrical device designed to store electric charge and electrical potential energy, typically consisting of two conducting plates separated by a dielectric or vacuum.

Capacitance

The charge stored per unit of electrical potential difference between the conducting plates of a capacitor: $C = \frac{Q}{V}$.

Faraday's law of electromagnetic induction

The magnitude of the induced electromotive force ($\text{emf}$) in a circuit is directly proportional to the rate of change of magnetic flux linkage through the circuit.

Lenz's law

The direction of an induced electromotive force or induced current always produces effects that oppose the change in magnetic flux that created it.

Step-down transformer

A transformer designed to produce an output (secondary) voltage that is lower than the input (primary) voltage by having fewer secondary windings than primary windings.

Critical angle

The angle of incidence in an optically denser medium that results in an angle of refraction of $90^\circ$ in the optically less dense medium.

Total internal reflection

The complete reflection of a light ray back into the optically denser medium when the angle of incidence exceeds the critical angle at a boundary with a less dense medium.

Dispersion

The separation of white light into its component spectral colours when passing through a medium due to different frequencies having different speeds and angles of refraction.

Photon

A discrete packet or quantum of electromagnetic energy, with energy given by $E = hf$.