Physical Sciences Grade 12 Examination Guidelines 2021

Flashcards based on the 2021 Grade 12 Physical Sciences Examination Guidelines, covering key terminology, laws, and definitions for both Physics and Chemistry.

Normal force ($N$)

The force or the component of a force which a surface exerts on an object with which it is in contact, and which is perpendicular to the surface.

Frictional force ($f$)

The force that opposes the motion of an object and which acts parallel to the surface.

Static frictional force ($f_s$)

The force that opposes the tendency of motion of a stationary object relative to a surface.

Kinetic frictional force ($f_k$)

The force that opposes the motion of a moving object relative to a surface.

Newton's first law of motion

A body will remain in its state of rest or motion at constant velocity unless a non-zero resultant/net force acts on it.

Newton's second law of motion

When a non-zero net force acts on an object, the object will accelerate in the direction of the force and the acceleration is directly proportional to the force and inversely proportional to the mass of the object.

Newton's third law of motion

When object A exerts a force on object B, object B simultaneously exerts an oppositely directed force of equal magnitude on object A.

Newton's Law of Universal Gravitation

Each body in the universe attracts every other body with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

Weight

The gravitational force the Earth exerts on any object on or near its surface.

Momentum ($p$)

The product of an object's mass and its velocity ($p = m v$).

Newton's second law of motion (in terms of momentum)

The net (or resultant) force acting on an object is equal to the rate of change of momentum of the object in the direction of the net force (F_{net} = rac{\Delta p}{\Delta t}).

Impulse

The product of the resultant/net force acting on an object and the time the net force acts on the object ($F_{net} \Delta t$).

Isolated system

A system on which the net external force is zero.

Principle of conservation of linear momentum

The total linear momentum of an isolated system remains constant (is conserved).

Projectile

An object which has been given an initial velocity and then it moves under the influence of the gravitational force only.

Free fall

Motion during which the only force acting on an object is the gravitational force.

Work ($W$)

The work done on an object by a constant force $F$ is $F \Delta x \cos(\theta)$, where $F$ is the magnitude of the force, $\Delta x$ the magnitude of the displacement and $\theta$ the angle between the force and the displacement.

Work-energy theorem

The net work done on an object is equal to the change in the object's kinetic energy ($W_{net} = \Delta K = K_f - K_i$).

Conservative force

A force for which the work done in moving an object between two points is independent of the path taken; examples include gravitational, elastic, and electrostatic forces.

Non-conservative force

A force for which the work done in moving an object between two points depends on the path taken; examples include frictional force, air resistance, and tension.

Principle of conservation of mechanical energy

The total mechanical energy (sum of gravitational potential energy and kinetic energy) in an isolated system remains constant.

Power ($P$)

The rate at which work is done or energy is expended ($P = \frac{W}{\Delta t}$).

Doppler effect

The change in frequency (or pitch) of the sound detected by a listener, because the sound source and the listener have different velocities relative to the medium of sound propagation.

Coulomb's law

The magnitude of the electrostatic force exerted by one point charge ($Q_1$) on another point charge ($Q_2$) is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance ($r$) between them ($F = \frac{k Q_1 Q_2}{r^2}$).

Electric field

A region of space in which an electric charge experiences a force.

Electric field at a point

The electrostatic force experienced per unit positive charge placed at that point ($E = \frac{F}{q}$).

Ohm's law

The potential difference across a conductor is directly proportional to the current in the conductor at constant temperature ($R = \frac{V}{I}$).

Electromotive force (emf)

The maximum energy provided by a battery per unit charge passing through it.

rms potential difference ($V_{rms}$)

The AC potential difference which dissipates/produces the same amount of energy as an equivalent DC potential difference ($V_{rms} = \frac{V_{max}}{\sqrt{2}}$).

rms current ($I_{rms}$)

The alternating current which dissipates/produces the same amount of energy as an equivalent direct current ($I_{rms} = \frac{I_{max}}{\sqrt{2}}$).

Photo-electric effect

The process whereby electrons are ejected from a metal surface when light of suitable frequency is incident on that surface.

Threshold frequency ($f_0$)

The minimum frequency of light needed to emit electrons from a certain metal surface.

Work function ($W_0$)

The minimum energy that an electron in the metal needs to be emitted from the metal surface.

Atomic absorption spectrum

A spectrum formed when certain frequencies of electromagnetic radiation passing through a substance are absorbed, appearing as dark lines in a continuous spectrum.

Atomic emission spectrum

A spectrum formed when certain frequencies of electromagnetic radiation are emitted due to an atom making a transition from a higher energy state to a lower energy state.

Molar volume of gases

$1\,\text{mole}$ of any gas occupies $22,4\,dm^3$ at $0\,^{\circ}\text{C}$ ($273\,K$) and $1\,\text{atmosphere}$ ($101,3\,kPa$).

Dipole-dipole forces

Intermolecular forces between two polar molecules.

Induced dipole forces (London forces)

Intermolecular forces between non-polar molecules.

Hydrogen bonding

Forces between molecules in which hydrogen is covalently bonded to nitrogen, oxygen or fluorine.

Boiling point

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

Melting point

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

Vapour pressure

The pressure exerted by a vapour at equilibrium with its liquid in a closed system.

Hydrocarbon

Organic compounds that consist of hydrogen and carbon only.

Homologous series

A series of organic compounds that can be described by the same general formula or in which one member differs from the next with a $CH_2$ group.

Saturated compounds

Compounds in which there are no multiple bonds between $C$ atoms in their hydrocarbon chains.

Unsaturated compounds

Compounds with one or more multiple bonds between $C$ atoms in their hydrocarbon chains.

Functional group

A bond or an atom or a group of atoms that determine(s) the physical and chemical properties of a group of organic compounds.

Structural isomer

Organic molecules with the same molecular formula, but different structural formulae.

Chain isomers

Structural isomers with the same molecular formula but different types of chains (e.g., butane and $2\text{-methylpropane}$).

Positional isomers

Structural isomers with the same molecular formula but different positions of the side chain, substituents, or functional groups on the parent chain.

Functional isomers

Structural isomers with the same molecular formula but different functional groups (e.g., methyl methanoate and ethanoic acid).

Heat of reaction ($\Delta H$)

The energy absorbed or released in a chemical reaction.

Exothermic reactions

Reactions that release energy, where \Delta H < 0.

Endothermic reactions

Reactions that absorb energy, where \Delta H > 0.

Activation energy

The minimum energy needed for a reaction to take place.

Activated complex

The unstable transition state from reactants to products.

Reaction rate

The change in concentration of reactants or products per unit time ($\text{Rate} = \frac{\Delta c}{\Delta t}$).

Catalyst

A substance that increases the rate of a chemical reaction without itself undergoing a permanent change by providing an alternative path of lower activation energy.

Chemical equilibrium

A dynamic equilibrium when the rate of the forward reaction equals the rate of the reverse reaction in a closed system.

Le Chatelier's principle

When the equilibrium in a closed system is disturbed, the system will re-instate a new equilibrium by favouring the reaction that will oppose the disturbance.

Arrhenius theory (Acids)

Acids produce hydrogen ions ($H^+ / H_3O^+$ / hydronium ions) in aqueous solution.

Arrhenius theory (Bases)

Bases produce hydroxide ions ($OH^-$) in aqueous solution.

Lowry-Brønsted theory (Acid)

An acid is a proton ($H^+$ ion) donor.

Lowry-Brønsted theory (Base)

A base is a proton ($H^+$ ion) acceptor.

Strong acids

Acids that ionise completely in water to form a high concentration of $H_3O^+$ ions (e.g., $HCl$, $H_2SO_4$, and $HNO_3$).

Strong bases

Bases that dissociate completely in water to form a high concentration of $OH^-$ ions (e.g., $NaOH$ and $KOH$).

Ampholyte

A substance that can act as either acid or base (e.g., water).

Hydrolysis

The reaction of a salt with water.

Equivalence point of a titration

The point at which the acid/base has completely reacted with the base/acid.

Endpoint of a titration

The point where the indicator changes colour.

Ion product of water ($K_w$)

The equilibrium constant for the ionisation of water: $K_w = [H_3O^+][OH^-] = 1 \times 10^{-14}$ at $298\,K$.

Oxidation

The loss of electrons or an increase in oxidation number.

Reduction

The gain of electrons or a decrease in oxidation number.

Oxidising agent

A substance that is reduced or gains electrons.

Reducing agent

A substance that is oxidised or loses electrons.

Anode

The electrode where oxidation takes place.

Cathode

The electrode where reduction takes place.

Electrolyte

A substance of which the aqueous solution contains ions or a substance that dissolves in water to give a solution that conducts electricity.

Galvanic cell

A cell in which chemical energy is converted to electrical energy.

Electrolytic cell

A cell in which electrical energy is converted into chemical energy.

Electrolysis

The chemical process in which electrical energy is converted to chemical energy or the use of electrical energy to produce a chemical change.