# 0.6 Lorentz force  (Page 3/4)

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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.

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 $3X{10}^{7}$ m/s in a magnetic field of $5X{10}^{-3}$ T. If velocity and magnetic field are perpendicular to each other, then magnetic force on the electron is :

${F}_{M}=qvB=1.6X{10}^{-19}X3X{10}^{7}X5X{10}^{-3}=2.4X{10}^{-14}\phantom{\rule{1em}{0ex}}N$

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 :

$a=\frac{{F}_{M}}{m}=\frac{2.4X{10}^{-14}}{9.1X{10}^{-31}}=2.6X{10}^{16}\phantom{\rule{1em}{0ex}}m/{s}^{2}$

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.

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.

anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Berger describes sociologists as concerned with
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