revision notes (last minute)

Some materials gain an electrostatic charge when rubbed together. opposite charges attract, like repel

Electric current is the flow of charge arouond the circuit

The potential difference between 2 points in an electronic circuit is the work done (energy transferred) per coulomb of charge that passes through the points

Circuit symbols represent electrical components

Resistance is a measure of how difficult it is for electrons to pass through a component

Current must pass through all components in a series circuit one after the other. Current in parallel can take more than one route

the resistance of a filament lamp increases as its temperature increases

An LED (light emitting diode) produces light when a current flows through it, and is efficient and long-lasting.

The resistance of an LDR (light-dependant resistor) varies with intensity of light. LDR's are used in switches

The resistance of a thermistor varies as its temperature changes. thermistors are often used in temperature sensors

Electric current has two forms; direct current (d.c) usually produced by batteries or cells alternating current (a.c) such as UK mains electricity (230 V a.c with frequency 50 Hz)

UK three-pin plugs contain a live wire (brown), a neutral wire (blue), an earth wire (green and yellow), and a fuse. Fuses, earth wires, and circuit breakers are safety devices

When an electric charge flows through a resistor, energy is transferre. Larger appliences need larger power cables. the power of an appliance is its rate of energy transfer.

Atoms have small central nucleus of protons (positively charged) and neutrons (no charge) surrounded by negatively charged elesctrons in orbit. Positively or negatively charged ions are created when atoms gain or lose electrons

Isotopes are atoms with the same number of protons/atomic number but a different number of neutrons

Radioactive decay is the breakdown of the nucleus of an atom to formionising radiation. Half-life is the average time taken for activity (decays per second) to halve

Nucleur fission is used in nuclear reactors to produce electricity

Nucleur fusion produces energy in stars

Rate of reaction is the change in amount of product (or reactant) per second

Reactions are faster at higher temperatures, at high concentration and high pressure, and with powdered solids.

Activation energy is the minimum amount of energy particles need to react

Catalyst increase the rate of a reaction but are unchanged at the end. they reduce the cost of industrial reaction

some reactions (e.g. combustion) are exothermic (transfer energy to the surroundings)

Some reactions (e.g. thermal decomposition) are endothermic (takes in energy from surroundings)

Reversable reactions are endothermic in one direction and exothermic in the other

Acids have a pH of less than 7 and are neutralised by bases

Metal oxides or hydroxides are bases, ammonia is also a base

Alkalis are bases dissolved in water. they have a pH of greater than 7

Acids contain H+ ions, alkalis contain OH- ions. these react to form water

Salt form when acids react with bases, alkalis or reactive metals

Soluble salts are prepared by neutralisation followed by crystallisation

Insoluble salts are made by precipitation reactions

Precipitation is used in water treatment

in electrolysis an electric current is passed through an ionic compound (molten or in soluation) . the compound breaks down into elements

Reduction happens at the negative electrode. Positive ions gain electrons. (RED CAT)

Oxidation happens at the positive electrode. Negative ions lose electrons

Metal objects are electroplated by making them a negative electrode and placing them in a solution of suitable ions

Aluminium is extracted by electrolysis of molten bauxite dissolved in cryolite

Electrolysis of brine produces chlorine, sodium hydroxide, and hydrogen

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