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Electric current (Components and their characteristics (• The…
Electric current
Current and charge
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• Current is caused by the flow of charged particles called charge carriers which can be conduction electrons in metals or ions in solution
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• ΔQ = IΔT where Q = charge (C), I – current (A) and T – time (s)
• Insulator - each electron attached to an atom and cannot move away from the atom – when pd applied across an insulator no current passes through as no free electrons
• Metallic conductor - some delocalised electrons which can carry a pd – these electrons attracted to +ve terminal of metal
• Semiconductor - number of charge carriers increases with temperature increase therefore as temp raised its resistance decreases
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Resistance
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• Ohm’s law - the pd across a metallic conductor is proportional to the current through it, provided the physical conditions don’t change
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• ρ = RA / L where A is cross-sectional area, L is length and R is resistance
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• A superconductor is a wire or device made of material which has 0 resistivity below a critical temperature
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• Superconductors used to make high-power electromagnets that generate very strong magnetic fields in devices such as MRI scanners and particle accelerators
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