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ELECTRICAL SYSTEMS (electric current (I) (electromotive force (use…
ELECTRICAL SYSTEMS
electric current (I)
conductors
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eg, metals: copper, iron, aluminium
insulator
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eg, non metals: plastic, rubber, glass, wood
circuit wires made of metal. to get electric current, electrons in metal atoms move from one atom to next in wires
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electromotive force
battery does not supply water in pipe, but it works to drive electrons around circuit
emf of electrical energy source defined as work done by source in driving unit charge around complete circuit
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use voltmeter
positive and negative terminals should be connected to positive and negative terminals respectively of electrical source (Like bulb)
electric circuits
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series
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if one bulb is removed/broken, no current flows, and other bulbs do not light up because circuit is now open
parallel
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if one bulb is removed or broken, other bulbs remain lit because circuit remains closed
resistance
electrical components in circuit act as obstacle against flow of electrons. components are said to have resistance
higher resistance in component--higher potential difference needed to move electric charge through component
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greater ratio of V to I, greater resistance
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resistors
electric circuits in equipment (eg tv) will operate properly only if correct amount of current flows in circuits
to control amount of current, electrical components called resistors used in circuits
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variable resistors
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as resistance changes, current also changes. higher resistance, lower current vice versa
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radio type 
light dimmer, volume control on music player, speed control of model train
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in order of dimmest to brightest: 2 similar resistors in series, circuit with single resistor, two similar resistors in parallel
potential difference
between two points: measure of amount of energy that is changed into other forms of energy when unit of charge passes between these two points
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electron leaving negative terminal of electric cell has higher (electrical) potential energy. at other points in circuit, its electrical potential energy is lower
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in electrical appliances, electric cells are connected in series with positive terminal of one cell touching negative terminal of next cell. as no. of electric cells in series increases, voltage increases. total voltage across all electric cells is equal to sum of voltages of individual cells
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electric circuit is system where all parts are working together, with changes made to one part of circuit affecting system as a whole
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