Ch 03 - Current Electricity12th Physics
Defining Electric Current (Variable Flow)
How is electric current formally defined in a conductor when the rate of charge flow varies with time?
How is electric current formally defined in a conductor when the rate of charge flow varies with time?
Explanation:
When the rate of flow of charge is not steady, we define the current at a specific instant.
The current at time is the mathematical limit of the ratio of net charge flowing across a cross-section to the time interval , as approaches zero.
SI Unit: Ampere (A), where .
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Instantaneous Electric Current
Instantaneous Electric Current
State the mathematical formula for instantaneous electric current using limits.
Variables & Units:
- I = Instantaneous electric current (Amperes, A)
- = Net charge flowing across the cross-section (Coulombs, C)
- = Time interval (seconds, s)
Conditions/Notes:
- The conventional direction of electric current is the direction of motion of positive charge.
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Scalar Nature of Current
Although electric current has a specified physical direction of flow in a wire, why is it strictly classified as a scalar quantity rather than a vector?
Although electric current has a specified physical direction of flow in a wire, why is it strictly classified as a scalar quantity rather than a vector?
Explanation:
Electric current does not obey the laws of vector addition (like the parallelogram or triangle laws).
When two currents meet at a junction, they simply add algebraically () according to Kirchhoff's Junction Rule (Conservation of Charge), regardless of the geometric angle between the joining wires.
Mathematically, current is the dot product of two vectors (Current Density and Area Vector), yielding a scalar: .
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Also in this chapter
41 more cards to study in Prism
- 4Ohm's Law (Scalar Form)
- 5Microscopic Mechanism of Current in Metals
- 6Resistance and Resistivity
- 7Thermal Velocity vs. Drift Velocity
- 8Current Density
- 9Ohm's Law (Vector Form)
- 10Drift Velocity Formula
- 11Current Density in Neutral Conductors
- 12Current and Drift Velocity Relation
- 13Microscopic Form of Resistivity
- 14Electron Mobility
- 15Limitations of Ohm's Law
- 16Temperature Dependence of Resistivity
- 17Resistivity: Metals vs. Semiconductors
- 18Electrical Power Dissipation
- 19Resistivity Orders of Magnitude
- 20Terminal Voltage of a Cell
- 21Carbon Resistor Color Codes
- 22Equivalent EMF: Cells in Series
- 23Standard Resistance Coils (Alloys)
- 24Equivalent EMF: Cells in Parallel
- 25Relaxation Time Dependencies
- 26Wheatstone Bridge Balance Condition
- 27Superconductivity Phase Transition
- 28Unknown Resistance via Meter Bridge
- 29High Voltage Power Transmission
- 30Potential Gradient
- 31Electromotive Force (EMF)
- 32Comparing EMFs using Potentiometer
- 33Internal Resistance via Potentiometer
- 34Kirchhoff's Junction Rule (KCL)
- 35Kirchhoff's Loop Rule (KVL)
- 36Temperature Dependence of Resistance
- 37Meter Bridge Principle
- 38Electrical Conductivity Formula
- 39Conductivity and Mobility Relation
- 40Potentiometer Working Principle
- 41Equivalent Resistance (Series & Parallel)
- 42Mixed Grouping of Identical Cells
- 43Potentiometer vs. Voltmeter for EMF
- 44Advantage of the Null Point Method
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