Current Electricity 12 Physics — Revision Notes
Electric current is the flow of charge through a conductor. Understanding current, resistance, and circuits forms the basis for practical applications of e
TL;DR: Electric current is the flow of charge through a conductor. Understanding current, resistance, and circuits forms the basis for practical applications…
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Electric current is the flow of charge through a conductor. Understanding current, resistance, and circuits forms the basis for practical applications of e
Electric Current
- Electric current is rate of flow of charge: I equals Q divided by t
- Unit of current is ampere (A)
- Conventional current flows from positive to negative terminal
- Electron flow is opposite to conventional current direction
- Current is due to movement of free electrons in conductor
Resistance and Ohm's Law
- Resistance is opposition to flow of current through conductor
- Ohm's Law: V equals I times R
- Resistivity is property of material: R equals rho times L divided by A
- Resistance depends on length, area, and resistivity of material
- Unit of resistance is ohm (Ω)
Resistivity and Temperature
- Resistivity increases with temperature for most conductors
- Formula: rho equals rho0 times (1 plus alpha times (T minus T0))
- alpha is temperature coefficient of resistivity
- Superconductors have zero resistance at very low temperatures
- Semi-conductors have resistivity between conductors and insulators
Series and Parallel Circuits
- Series: same current flows through all components; voltages add
- Total resistance in series: R equals R1 plus R2 plus R3
- Parallel: same voltage across all components; currents add
- Total resistance in parallel: 1/R equals 1/R1 plus 1/R2 plus 1/R3
- Parallel circuits allow independent operation of components
EMF and Internal Resistance
- EMF is electromotive force; maximum potential difference of source
- Internal resistance reduces output voltage of real battery
- Terminal voltage equals EMF minus current times internal resistance
- V equals E minus Ir
- Ideal battery has zero internal resistance
Key Terms
- Electric Current: Flow of charge through a conductor measured in amperes
- Resistance: Opposition to flow of electric current through a conductor
- Ohm's Law: Relationship stating voltage equals current times resistance
- EMF: Electromotive force; maximum potential of an electrical source
Frequently Asked Questions
Why does resistance of a conductor increase with temperature?
Higher temperature increases vibration of atoms. These vibrations obstruct electron flow, increasing resistance. This effect is quantified by temperature coefficient of resistivity.
What is the advantage of parallel circuits over series circuits?
In parallel circuits, each component gets full voltage and operates independently. If one component fails, others continue working. In series, all components share voltage and failure of one breaks the circuit.
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