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thermistorsinsulators and semi-conductors behave in a different way when the temperature increases because their resistivity decreases that is the
electrical measuring instrumentsquantities of electrical current voltage and resistance are measured using instruments called meters until the advent
ohmrsquos lawso far you have been introduced to the concepts of electric current as a movement of free electrons through a conducting material
small alkaline cellshermetically sealed ni-cad cells are produced in the same size and shape as their primary counterparts they are small portable
charge and discharge characteristics of nickel cadmium cellduring charging and discharging the electrolyte acts only as an ionised conductor
common lead acid battery faultscareful treatment of lead acid batteries prevents damage and early failure however some common faults associated with
the charge and discharge characteristics of lead batteryduring discharge the plates are converted into lead sulphate the water content of the
interconnection of cellscells may be connected in series parallel or any combination of the two in order to form a battery when cells are connected
cell capacitythe amount of electrical energy that a cell can provide from new to the end of its useful voltage on load is called the cell capacity
cell emfthe size of a cell has no bearing on the emf that it will produce the generated emf being determined solely by the materials used in its
production of electricity by lightthe photovoltaic cell or solar cell a photovoltaic cell generates an emf when light falls onto it several forms
production of electricity by pressurecertain crystals and semiconductors produce an emf between two opposite faces when the mechanical pressure on
production of electricity very large amounts of electrical energy lie dormant in the atoms of every speck of material in the universe whilst the
resistancean electric current is a flow of free electrons through a conductor the size of current flowing through a conductor for a given applied
movement of chargealthough electric current is referred to as the flow of electrons through a conductor it should be noted that more exactly any
electromotive force ndash emfto make use of electricity by provision of an electric current the potential different must be maintained that is the
potential differencewhen charges move from one point to another it is not the actual values of potential at those points which are important but the
voltagevoltage is the electrical equivalent of mechanical potential if a person drops a rock from the first storey of a building the velocity it
attraction amp repulsion of atomit can be observed that if two negatively charged bodies are brought together there is a force of repulsion between
energy levelsthe energy levels measured in electron volts ev in which orbiting electrons exist comply with a law of physics which states that energy
ionisationif the amount of external energy is large enough the valence electron can gain sufficient kinetic energy energy of movement to be removed
electrical materialsmaterials which allow an electric current to flow easily are known as conductors and those which prevent the flow of an
particle functionprotonsthe number of protons in an atom determines the kind of materialeghydrogen 1 protonhelium 2 protons lithium 3 protons
atomsif a water molecule could be magnified sufficiently it would be seen to consist of three smaller particles closely bound together these three
moleculeslet us take a piece of matter for example a drop of water and see what happens when it is sub-divided into smaller and smaller portionsthe