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Electricity (Identification of Hazards (Frayed cables (Exposed bare wires,…
Electricity
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Ohm's Law
For certain components (described as ohmic), ohmic law is obeyed
For an ohmic conductor at constant temperature, the current through it is proportional to the potential difference across it
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Non-Ohmic Components
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Filament lamp
Current flows
» filament gets hotter
» metal atoms vibrate faster and further
» ^ collisions
» more resistance
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As current increases, resistance increases
Diode
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A diode has two resistances depending on which way it is connected, KA polarity
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Electrical Energy:
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Energy can be used usefully, eg. motor lifting load, or wasted, eg. heat from a resistor
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Fuse
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Large current passes through it (due to fault)
» gets very hot and melts, breaking the circuit
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Domestic Wiring
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Earth – yellow / green
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If there's a fault with equipment and live wire touches metal,
» very large current will flow down the live wire and back via the earth to a grounding point
» fuse melts
» breaks the circuit
Heating Elements
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Eg. electric fires, electric cooker hobs, kettle, iron etc.
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(Double) Insulation:
Some appliances don't have an earth wire, they have a plastic casing
» the live wire cannot touch any exposed part
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