<< Chapter < Page Chapter >> Page >

Yet another important consequence of the nature of magnetic force is that a charged particle in magnetic field keeps changing direction of motion of the particle all the time. Since direction of velocity is changed every instant, direction of magnetic force being perpendicular to it is also changed all the time. Note that direction of magnetic force is automatically adjusted or changed with the motion. If the particle does not escape out of the magnetic field, the implication is that the particle may approximate a circular path. At any moment – whether particle completes a circular path or not – the magnetic force acts in radial direction to the motion. On a comparison note, we can see that the electric force is independent of the direction of motion. It is along electric field. It does not change with motion.

Lorentz magnetic force

Magnetic force changes direction as direction of motion changes.

We make use of this feature in many important applications like cyclotron to accelerate particle or entrapping plasma etc. But we should be aware of its role in these applications. The effect of Magnetic force is limited to change in direction only. Change in speed is effected by electric field.

Magnitude of magnetic force

The magnetic field is a weak field and so is the magnetic force. Let us consider an electron moving with a velocity 3 X 10 7 m/s in a magnetic field of 5 X 10 - 3 T. If velocity and magnetic field are perpendicular to each other, then magnetic force on the electron is :

F M = q v B = 1.6 X 10 - 19 X 3 X 10 7 X 5 X 10 - 3 = 2.4 X 10 - 14 N

Clearly, magnetic force is really very weak. However, even this weak force is great enough for subatomic particle like electron. For example, the acceleration of electron due to this magnetic force is :

a = F M m = 2.4 X 10 - 14 9.1 X 10 - 31 = 2.6 X 10 16 m / s 2

Indeed this is an extraordinary acceleration.

Context of lorentz force law

Lorentz magnetic force law completes the picture on “effect side” in the study of electromagnetism. The “cause side” i.e. generation of magnetic field is described by Biot-Savart law. Thus, Lorentz force law describes the effect of electric and magnetic fields on a test charge – but not the cause of these fields. This is a serious limitation because test charge on its own is also the cause of electric and magnetic fields. These fields, in turn, would modify the fields operating on the test charge.

Also, the electromagnetic force causes acceleration of test charge. An accelerated charge, in turn, radiates. As such, application of Lorentz force law by itself would not be sufficient to describe motion of test charge. A charged electron which is expected to describe a circular motion under magnetic field without consideration of radiation would actually spiral down with radiation as shown in the figure and expected motion might simply be not there.

Motion of charge under magnetic field

Motion of charge under magnetic field

Recall that this was the reason for which Rutherford’s atomic model was eventually rejected and Bohr’s model was accepted. We shall, however, ignore radiation while studying motion of charged particles under electromagnetic fields – unless state specifically to consider radiation.

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.
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Electricity and magnetism. OpenStax CNX. Oct 20, 2009 Download for free at http://cnx.org/content/col10909/1.13
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Electricity and magnetism' conversation and receive update notifications?