Current Electricity | Class 12 Physics Notes

3.3 ELECTRIC CURRENTS IN CONDUCTORS

Electric currents in conductors arise when free charges move under the influence of an electric field. While free charged particles exist naturally in the ionosphere, in solids, electrons and nuclei are generally bound within atoms and molecules. However, in metals, some electrons are practically free to move within the material, making metals good conductors. When an electric field is applied, these free electrons experience a force and drift, producing current. In solid conductors, current is mainly carried by negatively charged electrons moving against the electric field direction. Without an electric field, electrons move randomly due to thermal energy, resulting in zero net current because equal numbers move in all directions. Applying an electric field creates a force on electrons, causing them to drift and produce a net current. For example, a metallic cylinder with charges +Q and -Q placed at its ends creates an electric field inside, causing electrons to drift and neutralize the charges. This current lasts only briefly unless the charges at the ends are continuously replenished, as in batteries or cells, which maintain a steady electric field and thus a steady current.

📊 Diagram: FIGURE 3.1 Charges +Q and -Q put at the ends of a metallic cylinder. The electrons will drift because of the electric field created to neutralise the charges. The current thus will stop after a while unless the charges +Q and -Q are continuously replenished.

🔗 Connection: This section introduces the microscopic origin of current, leading to Ohm's law in the next section.