Introduction of Current Density
Have you ever wondered what current density is and how you can determine it? Before you can understand the current density formula, you must possess proper knowledge of current itself.
Defining Current
Current is the flow of electrons from an electrically abundant source to an electrically deficit destination. We use the symbol I to denote current, whereas ampere is the standard unit for measuring the same.
Current always follows in a specific direction of flow. Thus, you will find current flowing from a positive to a negative point.
What are AC and DC Current?
Before proceeding to learn what current density is, you should also be able to point out the differences between the two types of current – direct (DC) and alternating (AC).
Current Density Definition
Current density is referred to as the total amount of current which is flowing through one unit value of a cross-sectional area. If this is of uniform current flow, then the amount of current which is flowing through a specific conductor is the same at all points of the conductor, even if the conductor area differs.
Current density formula can help to determine the amount of current in a specific portion of the conductor.
What is the Current Density Formula?
Current Density (J) = I/A
In this equation, ‘I’ is the amount of current in Amperes while ‘A’ is the cross-section area in sq. meters.
Current Density Example
Now that you are aware of the formula for calculation, take a look at the example below to get a clearer idea.
Example – A 10mm2 of copper wire conducts a current flow of 2mA. Determine this current density using the current density formula.
Solution – In this example, current (I) = 2 x 10-3
A = 10 x 10-3
Thus, current density (J) = 2 x 10-3/10 x 10-3
J = 0.20 A/m2
What is the Unit of Current Density?
The SI unit of current density is Ampere/meter2. This unit also helps you remember the formula for calculation of such a density. Since Ampere is the unit of current and meter2 is the unit for measuring cross-sectional area, one can easily derive the formula for current density. It is the current flow divided by the area of the cross section.
Quick Exercise – 1
What is this density when 137 Ampere of current flows through a conductor cross-section, measuring 1.2m2?
Solution –
Here I = 137A
A = 1.2m2
Therefore, J = I/A
=> J = 137/1.2
=> J = 114.66 A/m2
What is the Relation between Current Density and Electric Field?
With the help of Ohm’s Law, you can determine a connection between electric field and current density.
We know I = nEavd
I = nAe(eE/m)
We know J = I/A
Now, I/A = ne2(E/m)
This is why charge density is so crucial in Physics. It relates to the electric field in electromagnetism.
True or False
Q. Unit of measuring frequency for alternating current is Joule.
Ans. False. The unit for measuring the frequencies of AC is Hertz and not Joule.
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FAQs on Current Density
1. Why is current density important ?
Current Viscosity is important to the design of electrical and electronic systems.
Circuit performance depends explosively upon the designed current position, and the current viscosity also is determined by the confines of the conducting rudiments. For illustration, as integrated circuits are reduced in size, despite the lower current demanded by lower bias, there's a trend toward advanced current consistency to achieve advanced device figures in ever lower chip areas. See Moore's law.
At high frequentness, the conducting region in a line becomes confined near its face which increases the current viscosity in this region. This is known as the skin effect.
High current consistency has undesirable consequences. Utmost electrical operators have a finite, positive resistance, making them dissipate power in the form of heat. The current viscosity must be kept sufficiently low to help the captain from melting or burning up, the separating material failing, or the asked electrical parcels changing. At high current consistency the material forming the interconnections actually moves, a miracle called electromigration. In superconductors, inordinate current viscosity may induce a strong enough glamorous field to beget robotic loss of the superconductive property.
The analysis and observation of current viscosity also is used to probe the drugs underpinning the nature of solids, including not only essence but also semiconductors and insulators. An elaborate theoretical formalism has developed to explain numerous abecedarian compliances.
The current viscosity is an important parameter in Ampère's circuital law (one of Maxwell's equations), which relates current viscosity to a glamorous field.
2. How current density is used in electrical wiring?
In electrical wiring, the maximum current viscosity can vary from 4 A ⋅ mm − 2 for a line with no air rotation around it, to 6 A ⋅ mm − 2 for a line in free air. Regulations for electrical wiring list the outside allowed current of each size of the string in differing conditions. For compact designs, similar to windings of SMPS mills, the value might be as low as 2 A ⋅ mm − 2. (15) If the line is carrying high-frequency currents, the skin effect may affect the distribution of the current across the section by concentrating the current on the face of the captain. In mills designed for high frequentness, loss is reduced if Litz line is used for the windings. This is made of multiple isolated cables in resemblance with a periphery twice the skin depth. The insulated beaches are twisted together to increase the total skin area and to reduce the resistance due to skin goods.
For the top and nethermost layers of published circuit boards, the maximum current viscosity can be as high as 35 A ⋅ mm − 2 with a bobby consistency of 35 μm. Inner layers can not dissipate as important heat as external layers; contrivers of circuit boards avoid putting high-current traces on inner layers.
In the semiconductors field, the maximum current consistency for different rudiments is given by the manufacturer. Exceeding those limits raises the following problems.
The Joule effect which increases the temperature of the element.
The electromigration effect which will erode the connection and ultimately beget an open circuit.
The slow prolixity effect which, if exposed to high temperatures continuously, will move metallic ions and dopants down from where they should be. This effect is also reverse to aging.
3. What is electromagnetism ?
Electromagnetic marvels are defined in terms of the electromagnetic force, occasionally called the Lorentz force, which includes both electricity and captivation as different instantiations of the same miracle. The electromagnetic force plays a major part in determining the internal parcels of utmost objects encountered in diurnal life. The electromagnetic magnet between infinitesimal capitals and their orbital electrons holds atoms together. Electromagnetic forces are responsible for the chemical bonds between atoms which produce molecules, and intermolecular forces. The electromagnetic force governs all chemical processes, which arise from relations between the electrons of bordering atoms. Electromagnetism is veritably extensively used in ultramodern technology, and electromagnetic proposition is the base of electric power engineering and electronics including digital technology.
4. Why is electron diffusion current positive ?
The prolixity current viscosity due to prolixity of electrons is given by Jn = (e) (Dn) (dn/ dx) The prolixity current viscosity due to prolixity of holes is given by Jp = - (e) (Dp) (dp/ dx)
I understand that for a semiconductor, Electron prolixity current viscosity and hole prolixity current viscosity are contrary to each other. So they will have the opposite sign. But why is electron prolixity current positive and hole prolixity current negative? (despite the fact that electron charge is -ve and pierce charge is + ve).
5. What is the electric field ?
Electric field, an electrical property related to each point in space when charge is present in any form. The magnitude and direction of the electrical field are expressed by the worth of E, called field strength or field intensity or just the electrical field. Knowledge of the worth of the electrical field to some extent , with no specific knowledge of what produced the sector , is all that's demanded to work out what is going to be electric charges near that particular point.
6. How can you define current density?
Current density refers to the amount of charge flowing through a specific cross-sectional area of a conductor. The amount tends to remain constant in case of a steady charge flow. Nevertheless, this cross-sectional area of a conductor differs, which, in turn, leads to varying density.
7. Is current density scalar or vector quantity?
Current density is a vector quantity even though it is a combination of two scalar quantities.
8. What is the symbol for current density?
This density is represented by ‘J’. Its unit, on the other hand is Ampere/meter2 or A/m2.