9.1 Electrical Current

Electrical current is the flow of electric charge through a conductor, driven by a difference in electric potential. It's measured in amperes, with one ampere defined as the flow of one coulomb of charge per second.

Conventional current flows from positive to negative, opposite to electron flow. Understanding current is crucial for analyzing circuits and electrical systems, forming the foundation for more complex concepts in electromagnetism.

Electrical Current

Definition of electrical current

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• Flow of electric charge through a conductor
  • Charge carriers (electrons or ions) move through the conductor
  • Conductors (metals) allow charge to flow easily
• Current flows from higher electric potential (voltage) to lower electric potential
  • In a battery, current flows from positive terminal to negative terminal
• Conventional current direction defined as flow of positive charge
  • In reality, electrons (negative charge) flow opposite to conventional current

Unit of electrical current

• Ampere (A) is the unit of electrical current
  • One ampere defined as flow of one coulomb (C) of charge per second
  • $1 \text{ A} = 1 \text{ C/s}$
• Relationship between current ($I$), charge ($Q$), and time ($t$) given by:
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  • 10 coulombs of charge passing through a point in a circuit in 5 seconds results in a current of 2 amperes

Conventional current vs electron flow

• Conventional current defined as flow of positive charge
  • Historical convention still widely used in circuit analysis
  • In a battery-powered circuit, conventional current flows from positive to negative terminal
• Electron flow is actual movement of electrons (negative charge) in a conductor
  • Electrons are primary charge carriers in most conductors (metals)
  • Electrons flow from negative to positive terminal in a battery-powered circuit
• Direction of electron flow is opposite to direction of conventional current
  • Magnitude of current is the same in both cases

Current, Resistance, and Electric Field

• Ohm's law relates current, voltage, and resistance: $V = IR$
• Resistance opposes the flow of electric current in a conductor
• Electric field in a conductor drives the flow of charge carriers
• Drift velocity describes the average speed of charge carriers in response to the electric field
• Current density represents the amount of current flowing per unit cross-sectional area of a conductor