Charge and Current Flow in Different Conductors

Charge and Current Flow

Fundamental Concepts

  • Charge (Q):

    • Fundamental unit.

    • Measured in Coulombs (C).

  • Current (I):

    • Rate of flow of charge.

    • Expressed as dQ/dtdQ/dt.

    • Measured in Amperes (A).

Types of Current Conductors

A) Semiconductors

  • Classified into two types:

    • Intrinsic

    • Extrinsic

i) Intrinsic Semiconductors

  • Pure elemental solids (e.g., silicon).

  • Equal number of electrons and holes (positive charges).

ii) Extrinsic Semiconductors

  • Created by adding impurities to intrinsic semiconductors.

  • Two subtypes:

    • p-type

    • n-type

p-type Semiconductors

  • Formed by adding impurities like boron (B) to silicon.

  • Contain more positive charges (holes) than electrons.

  • Current flow is primarily due to the movement of positive charges (holes).

n-type Semiconductors

  • Formed by adding impurities like phosphorus to silicon.

  • Contain more electrons than positive charges (holes).

  • Current flow is primarily due to the movement of electrons.

  • Charge Flow (Current / A) in Semiconductors:

    • Depends on whether the semiconductor is n-type or p-type.

    • n-type: excess electrons act as charge carriers.

    • p-type: excess holes (positive charges) act as charge carriers.

  • Pure Semiconductor (e.g., Silicon):

    • When polarized, electron flow is opposite to the flow of holes (positive charges).

    • This occurs because there are equal numbers of electrons and holes.

B) Electronic Conductors

  • Examples: Metals (copper) and non-metals (graphite).

  • Electrons are the primary charge carriers.

  • Electrons reside in the Fermi level (highest energy level).

  • Electrons move from lower potential (-ve) to higher potential (+ve).

  • No positive charge flow in the opposite direction because there are no positive charges in electronic conductors.

C) Electrolyte or Ionic Solutions

  • Can exist in liquid state (liquid electrolyte), such as aqueous KCl solutions.

  • Can also exist in solid state (solid electrolytes), such as polymers and ceramic materials.

  • Charge carriers are ions (e.g., K+K^+ and Cl−Cl^- ions).

  • Current flow is due to the movement of ions to respective electrodes.

  • No free electrons or positive holes in electrolytes.