Current density is the total amount of current flowing per unit cross-sectional area, measured in amperes per square meter. When a small current flows through an infinitesimal area, a relationship between the current and the current density can be established, where theta is the angle between the area and the current density. Therefore, the total current passing through the area can be determined by integrating it over the area. Consider the magnitude of the current density and recall the equation of drift velocity. By substituting the terms, a relation between current density and drift velocity can be established. While current is a scalar quantity, current density is a vector quantity. Consider a current of 0.5 amperes flowing through a 50-watt bulb. The bulb is wired using a copper wire with a radius of 1.25 mm. Determine the magnitude of the current density. The known values are the current and cross-sectional area, whereas the current density is an unknown quantity. By substituting the known quantities into the equation, the current density can be determined.