4.1. Electric Current and Circuits (B5)

Direct current (dc) is the flow of charge carriers (usually electrons) through a conductor, moving from lower to higher electric potential.
In conductors, mobile electrons move freely, while in insulators, charge carriers are immobile, preventing current flow.
Electric potential difference (V) provides the energy that drives the movement of charges through a material.

Resistance (R) quantifies how much a material opposes the flow of current, and depends on its resistivity (ρ), length, and cross-sectional area
Ohm’s Law defines an ohmic conductor as one where V∝IV \propto IV∝I at constant temperature; non-ohmic materials (e.g., filament lamps) do not follow this.
Resistivity is a material property; conductors have low resistivity, insulators have high resistivity.

Electrical resistance causes heating of conductors, leading to energy loss as thermal energy
Resistance affects current and voltage drops across circuit elements, influencing the design and efficiency of electrical systems.
Real cells have internal resistance (r), reducing the terminal voltage below the emf when a current flows.

that cells provide a source of emf
chemical cells and solar cells as the energy source in circuits
that circuit diagrams represent the arrangement of components in a circuit
direct current (dc) I as a flow of charge carriers
that the electric potential difference V is the work done per unit charge on moving a positive charge between two points along the path of the current
the properties of electrical conductors and insulators in terms of mobility of charge carriers
electric resistance R and its origin
resistivity
Ohm's law
the ohmic and non-ohmic behaviour of electrical conductors, including the heating effect of resistors
electrical power P dissipated by a resistor
the combinations of resistors in series circuits
the combinations of resistors in parallel circuits
that electric cells are characterised by their emf and internal resistance r
that resistors can have variable resistance.