Current Electricity Mind Map

Electric current is the rate of flow of electric charge through a cross-section of a conductor. Drift velocity is the small average velocity with which free electrons move opposite to the applied electric field inside a conductor.

For derivations, clearly separate electron drift direction from conventional current direction, and write the final current relation as I = neAv_d with correct units.

Ohm's law states that the current through a conductor is directly proportional to the potential difference across it, provided temperature and other physical conditions remain constant. Resistivity is the material property that measures how strongly a substance opposes current flow.

In graph questions, a straight-line V-I graph through the origin indicates ohmic behaviour, and the slope of a V versus I graph gives resistance.

A combination of resistors is an arrangement of two or more resistors connected in a circuit so that they can be replaced by a single equivalent resistance producing the same current-voltage effect between two terminals.

Before calculation, mark whether current is common or voltage is common. This usually reveals whether the connection is series or parallel.

EMF of a cell is the work done by the source per unit charge in driving charge around the complete circuit. Internal resistance is the opposition to current within the cell, and terminal voltage is the potential difference available across the cell terminals when current flows.

State clearly whether the cell is discharging or charging before choosing the sign in the terminal voltage relation.

Kirchhoff's junction rule states that the algebraic sum of currents at a junction is zero, based on conservation of charge. Kirchhoff's loop rule states that the algebraic sum of potential changes around any closed loop is zero, based on conservation of energy.

If the calculated current is negative, do not panic. It means the actual current direction is opposite to the direction initially assumed.

A Wheatstone bridge is a four-resistor network used to compare resistances. It is balanced when no current flows through the galvanometer branch, giving the condition P/Q = R/S.

At balance, treat the galvanometer branch as carrying zero current. This allows the bridge network to be simplified using series relations in each arm.