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Magnetic field due to current in circular wire is largely axial. It means that we need to concentrate our investigation of magnetic field on axial positions. One of the important axial positions is center of the circular wire itself. We shall limit our discussion in this module to this case of magnetic field at the center of circular coil. The procedure for deriving expression for the magnetic field due to current in circular wire is same as that of current carrying straight wire. Here also, we make use of superposition principle whereby we combine the small magnetic fields due to each of the small current elements composing the circular coil.

Circular wire is considered to be composed of small linear current elements. We determine magnetic field due to each of the linear current elements applying Biot-Savart law. Finally, we determine net magnetic field using superposition principle (i.e. by determining vector sum of magnetic fields due to all current elements).

In general, the bending of current carrying wire in circular shape has the effect of strengthening or localizing magnetic field in narrower region about the axis.

Direction of magnetic field (right hand thumb rule)

Let us consider two diametrically opposite small current elements on the circular wire. The magnetic field lines are compressed inside the circle as it accommodates all the circular closed lines drawn outside. This compression of magnetic field lines is maximum at the center. In the figure here, we consider the circular coil in horizontal plane. The magnetic field lines being perpendicular to current elements are in the plane of drawing.

Magnetic field due to current in circular wire

Magnetic field lines due to oppositely placed current elements

Such is the case with any other pair of current elements as well. This means that magnetic field line passing though axis is reinforced by all such diametrically opposite pairs of current element. The magnetic field due to current in circular wire, therefore, is nearly axial.

The observations as above are the basis of Right hand thumb rule for current in circular wire. If we orient right hand such that curl of fingers follows the direction of current in the circular wire, then extended thumb points in the direction of magnetic field at its center.

Right hand thumb rule

If we orient right hand such that curl of fingers follows the direction of current in the circular wire, then extended thumb points in the direction of magnetic field at its center.

Right hand thumb rules for straight wire and circular wire are opposite in the notations. The curl of hand represents magnetic field in the case of straight wire, whereas it represents current in the case of circular wire. Similarly, the extended thumb represents current in the case of straight wire, whereas it represents magnetic field in the case of circular wire.

There is yet another simple way to find the direction of axial magnetic field at the center. Just look at the circular loop facing it. If the current is clockwise, then magnetic field is away from you and if the current is anticlockwise, then magnetic field is towards you.

Questions & Answers

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Electricity and magnetism. OpenStax CNX. Oct 20, 2009 Download for free at http://cnx.org/content/col10909/1.13
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