Current Density

Current is used to operate a wide range of equipment, from simple fans to more complicated boilers and heaters. The flow of electrical charge carriers is defined as current. Current density is the amount of electric current moving per unit cross-section area and is measured in amperes per square metre. Moreover, the current density is a vector quantity with both direction and scalar magnitude.

The current density in a conductor increases as the current in the conductor increases. However, the current density varies in various regions of an electrical conductor, and this phenomenon occurs with higher-frequency alternating currents.

What is current density? 

The entire amount of current flowing through one unit value of a cross-sectional area is referred to as current density. When the current flow is uniform, the quantity of current flowing through a particular conductor is the same at all places along the conductor, even if the conductor area varies.

The current density is inversely related to the conductor’s cross-sectional area and directly proportional to the amount of current travelling through it. As a result, the larger the current, the higher the current density value. Similarly, a conductor with a high cross-sectional area would have a lower current density for the same amount of current running through it as a conductor with a smaller cross-sectional area.

The current density is the same at every point on a precisely uniform conductor with identical dimensions and cross-sectional area throughout. This is true for the vast majority of current-carrying cables we see in our daily lives. Due to the nature of the wire we utilise, the direction of the current density can shift freely.

The direction of current density is assumed to be the same as the positive charge’s motion. This is a convention that corresponds to the current’s traditional flow.

Formula

The current density formula can be used to calculate the amount of current flowing through a certain section of a conductor.

Current Density (J) = I/A

‘I’ stands for the quantity of current in Amperes, and ‘A’ stands for the cross-section area in square metres in this equation.

The SI unit for current (I) is the ampere, while the unit for conductor cross-sectional area is m. A/m2 is the SI unit for the conduction current density formula.

Importance of current density

In every electrical or electronic system, the notion of current density is crucial. The current density determines the power output and efficiency of any circuit. The dimensions of the pre-defined or pre-measured circuits are used to calculate current density in most circuits.

The current density of an electrical circuit is also taken into account while assessing its safety. Circuits with a high current density are prone to overheating and breakdown, which might result in a complete disaster for the workers involved. Current density should be controlled within tolerable ranges to sustain the material’s conductive qualities. The conductive characteristics of conductors alter slightly at increasing temperatures.

This can have an adverse effect on the circuit’s performance, and in the event of a precisely calibrated circuit, it can irreversibly disrupt the circuit’s balance. The conductor’s insulating coat is also affected by high temperatures. The current-carrying conductor can become exposed to human contact if the outer insulating coating is damaged, resulting in electrocution.

The design of electrical and electronic systems relies heavily on current density. High current densities result in a magnetic field that is sufficiently powerful. If the magnetic field’s magnitude grows too big, it may begin to interfere with the operation of the surrounding components. 

Due to electromagnetic interference, the materials that constitute the junction between the wires can move at high current densities. This process is known as electromigration. The current density that is unchecked and unregulated can cause superconductors to lose their superconductive characteristics. As a result, the current density in such circuits is constantly checked in order to preserve the circuit’s functionality.

Surface charge density

Measurement of electric charges collected across a surface is called surface charge density. Charges per unit surface area may be used to compute the surface charge density. Cm-2 or C/m2 is the SI unit for the surface current density formula. The surface current density formula is 

σ=q/A

Here, q represents the charge and A represents the surface area.

Conduction current density

The quantity of current or charges that pass across the conduction surface in time t is referred to as the conduction current density. The conduction surface is parallel to the current flow in this case.

Conduction current density formula Jc = σE.

Here, Jc denotes the conduction current density, E denotes the electric field and σ denotes the electrical conductivity. 

Conclusion

To summarise, the quantity of charge flowing through a certain cross-sectional area of a conductor is referred to as current density. In the event of a continuous charge flow, the quantity tends to remain constant. Despite this, the cross-sectional area of a conductor varies, resulting in changing density. The planned current location has a huge impact on circuit performance, and the current density is also influenced by the limits of the conducting rudiments. Ampère’s circuital law (one of Maxwell’s equations) connects current density to a glamorous field and includes current density as an essential parameter.