# 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.

what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
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Mahi
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Rafiq
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
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Kyle
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why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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research.net
kanaga
sciencedirect big data base
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Introduction about quantum dots in nanotechnology
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absolutely yes
Daniel
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Maciej
Abigail
for teaching engĺish at school how nano technology help us
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Do somebody tell me a best nano engineering book for beginners?
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NANO
how can I make nanorobot?
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what is fullerene does it is used to make bukky balls
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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
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