Science Exam revision

Electric charge

A fundamental property of protons and electrons, measured in coulombs (C).

Proton

A subatomic particle with a positive charge, located in the nucleus, that cannot move between objects.

Electron

A subatomic particle with a negative charge, located in shells around the nucleus, that can move between objects.

Neutron

A subatomic particle with no charge, located in the nucleus.

Static electricity

Electric charge that builds up on the surface of an insulator and stays there until released as a spark.

Rules of charge

Like charges repel and opposite charges attract.

Current electricity

Electric charge that flows continuously around a complete circuit powered by a voltage source.

Electric current (I)

The rate of flow of electric charge, measured in amperes (A), calculated as I = Q ÷ t.

Voltage (V)

The amount of energy given to each unit of charge, measured in volts (V); also called potential difference.

Resistance (R)

How strongly a component or material opposes the flow of current, measured in ohms (Ω).

Conductor

A material that lets current flow easily because it contains free electrons.

Insulator

A material that does not let current flow because its electrons are held tightly to their atoms.

Ammeter

A meter used to measure electric current, connected in series and requiring a very low resistance.

Voltmeter

A meter used to measure voltage, connected in parallel across a component and requiring a very high resistance.

Conventional current

The accepted direction of current flow from the positive terminal to the negative terminal.

Electron flow

The actual drift of electrons from the negative terminal to the positive terminal.

Multimeter

A single instrument that can measure voltage, current, and resistance.

Grounding (Earthing)

Connecting a charged object to the ground with a conductor to let electric charge drain safely.

Series circuit

A circuit where components are connected one after the other in a single loop, providing only one path for the current.

Ohm's law

The mathematical relationship between voltage, current, and resistance expressed as V = I × R.

Ohmic conductor

A component that produces a straight-line voltage-current graph through the origin, meaning its resistance remains constant.

Non-ohmic conductor

A component, such as a filament globe, that produces a curved voltage-current graph because its resistance changes as it heats up.

Series circuit current rule

Current is the exact same at every point in a series circuit.

Series circuit voltage rule

The supply voltage is shared between the components in a series circuit (V_supply = V1 + V2 + …).

Series circuit resistance rule

The total resistance is the sum of the individual resistances (R_total = R1 + R2 + …).

Parallel circuit

A circuit where components are connected on separate branches, giving the current more than one path to choose from.

Parallel circuit voltage rule

The voltage across every branch in a parallel circuit is the same as the supply voltage.

Parallel circuit current rule

The total current from the supply is equal to the sum of the branch currents (I_total = I1 + I2 + …).

Household wiring

Electrical systems in houses are wired in parallel so every appliance receives full voltage, can be switched independently, and stays on if another fails.

Electromagnet

A coil of insulated wire wrapped around an iron core that becomes a strong magnet when current flows through it.

Motor effect

The force felt by a wire carrying a current inside a magnetic field.

Electromagnetic induction

The process of generating a voltage in a coil by moving a magnet relative to it or spinning a coil in a magnetic field.

Generator

A device that takes kinetic energy in and gives electrical energy out, essentially a motor working in reverse.

Renewable energy source

An energy source that is replaced naturally as fast as we use it, such as sunlight, wind, and flowing water.

Non-renewable energy source

An energy source that took millions of years to form and will eventually run out, such as coal, oil, gas, and uranium.

Active wire

The brown wire in a three-pin plug that carries current from the supply at 240 V.

Neutral wire

The blue wire in a three-pin plug that acts as the return path completing the circuit back to the supply.

Earth wire

The green and yellow safety wire in a three-pin plug that connects the metal case of an appliance to the ground.

Double insulation

A safety feature in appliances with a plastic case and two separate layers of insulation around live parts, meaning an earth wire is not needed.

Fuse

A thin piece of wire connected in series that heats up, melts, and breaks the circuit if the current gets too high.

Circuit breaker

An automatic switch in the switchboard that trips and turns off when the current is too large, and can be reset.

Safety switch (RCD)

A device that compares active and neutral currents and cuts the power in under 0.03 seconds if a small current leaks.

Short circuit

A fault where the current finds an unintended path with almost no resistance, causing a huge, dangerous current.

Overload

Drawing more current than wiring was designed to carry by plugging too many appliances into one circuit or power board.

Power (P)

The rate at which energy is transferred, measured in watts (W), where 1 W = 1 J per second.

Useful energy

The output energy that a device is designed to produce, such as light from a lamp or movement from a motor.

Wasted energy

The output energy that is not wanted, usually ending up as heat that spreads into the surroundings.

Law of conservation of energy

Energy cannot be created or destroyed, only transformed from one form to another, so energy in equals useful energy out plus wasted energy out.

Efficiency

The fraction of input energy that becomes useful output energy, expressed as a percentage.

Atom

The smallest possible piece of any substance; makes up all matter.

Element

A substance made up of only one type of atom or molecule.

Compound

A substance made up of two or more different elements joined together by chemical bonds.

Molecule

Two or more atoms joined together by covalent bonds.

Pure substance

A substance made up of only one type of atom, compound, or molecule.

Mixture

A substance made up of two or more pure substances that are not bonded together.

Atomic number

The number of protons in an atom.

Mass number

The total number of protons and neutrons in the nucleus of an atom.

Nuclide symbol

A quick way of providing an element's symbol, atomic number, and mass number.

Electron configuration

The arrangement representing where electrons are located in the shells of an atom.

Physical change

A change that occurs when no new substance is produced.

Chemical change

A change that occurs when new substances are formed.

Corrosion

A chemical reaction that occurs when metals react with substances in the air or water.

Combustion

A reaction involving a fuel reacting with oxygen to produce heat, carbon dioxide, and water.

Lattice

A regular arrangement of large numbers of atoms formed by metallic and ionic bonding.

Groups (Periodic Table)

Vertical columns in the periodic table (numbered 1 to 18) where elements share the same number of outer shell electrons and similar chemical properties.

Periods (Periodic Table)

Horizontal rows in the periodic table (numbered 1 to 7) where elements have the same number of electron shells.

Lustre

A physical property describing how shiny a substance is.

Malleability

The ability of a substance to be bent or flattened into different shapes.

Ductility

The ability of a substance to be drawn out into a thin wire.

Conductivity

The ability of a substance to transfer heat or electricity.

Electron shell capacity

The maximum number of electrons each shell can hold, calculated using the formula 2n² where n is the shell number.

Signs of a chemical reaction

Visible or measurable evidence that a chemical reaction has occurred, such as a change in colour, gas release, temperature change, light/sound production, or a precipitate forming.

Word equation

A representation of a chemical reaction using the names of the reactants on the left and the products on the right, separated by an arrow.

Preventing rusting

Methods used to slow down or stop the rusting of iron and steel, such as surface coating (paint, oil) or galvanising (coating with zinc).