<< Chapter < Page Chapter >> Page >

Direction of magnetic force

Direction of magnetic force

The magnetic force in the downward direction tends to drift electron in downward direction following a parabolic path. This drifting polarizes the conductor strip electrically. We know that each infinitesimally small element of the conductor is electrically neutral. But, there is accumulation of negative charge at lower edge as electrons drift down due to magnetic force. Correspondingly, there is accumulation of positive charge at the upper edge as there is depletion of electrons exposing immobile positive atoms in that region. The process of polarization, however, continues only momentarily. At any moment, the opposite polarity of charges at the edges sets up an electric field. In this case, the electric field is directed from upper (positive edge) to lower edge (negative edge). This electric field, in turn, pulls electron upward.

Polarization of charges and electric field

Polarization of charges and electric field

The dynamic condition is brought under equilibrium when electric force equals magnetic force. Let “E” be the electric field at equilibrium,

e E = e v d B v d = E B

where v d is the drift velocity. Once the equilibrium is reached, electrons keep moving with the drift velocity as they would have moved in the absence of magnetic field. Here, the opposite edges of the conductor strip function as infinite charged plates. The electric field, E, is given as :

E = V a

where, “a” is the width of the conductor strip and “V” is the electrical potential difference between the edges of conductor strip. This potential difference between the edges is known as Hall’s potential. We can measure it by connecting a voltmeter to the edges of the conductor strip.

Numbers of free electrons per unit volume

The “Hall effect” can be used to measure numbers of electrons per unit volume in a conductor. We know that the drift velocity of an electron is :

v d = I n e A

where “n” is numbers of free electrons per unit volume and “A” is the cross section area of the strip. Substituting in the equation of equilibrium, we have :

v d = E B I n e A = E B

Substituting for “E”, we have :

I n e A = V a B n = I a B e A V

Also, the area A is product of width and thickness, A = ab. Hence,

n = I B e b V

The quantities in the right hand expression are either known or measurable. Thus, we are able to measure the numbers of free (conduction) electrons per unit volume using Hall’s effect.

Drift velocity

Use of Hall’s effect allows measurement of drift velocity as well. The magnitude of drift velocity is about 0.0003 m/s, which is quite a small value that can be measured in the laboratory. The determination of drift velocity uses a very simple technique based on the detection of Hall’s effect.

The idea here is to move the conductor strip carrying current in the direction opposite to the direction of drift velocity i.e. in the direction of conventional current in the presence of uniform magnetic field. The motion of conductor is adjusted such that the relative drift velocity of electron with respect to stationary magnetic field is zero. In this case, speed of conductor strip is equal to the drift speed of electron. Also, the magnetic force is zero as relative velocity of electrons with respect to stationary magnetic field is zero. In turn, there is no drifting of electron towards the edge of the conductor and the Hall potential is zero. Thus, we are able to detect when the velocity of conductor strip equals drift velocity of electron.

Questions & Answers

what is the specialize functions of the organs
Donieta Reply
what is the faction of photo receptors in the eye
Mutangana Reply
transduction of light to nervous impulses occurr it is located in the retina
Maureen
wat are e constituents of blood
marybertiny Reply
Can a cell be destroyed by the bacteria
Makhanya Reply
anamia. because of loss of blood
fon Reply
Name the element which is liquid
Sandeep Reply
hg
RC
CO2
Maureen
Bromine
Aaron
what is the dept of respiration plz?
Maureen
Maureen where are you from
Omokaro
mercury
VANESSA
bromine
VANESSA
which of the muscle can work with out getting tired?
nikkita
heart
Anam
Hg
Samiullah
what is the unit of muscles?
Samiullah
acid are organic or inorganic
Samiullah
why is the baby formed in the uterus n not else where?
Ekali Reply
you may help me ,to know why
mar
lo i am inn
mar
the womb is to protect the baby because inside the womb the lay in a fluid called the amniotic fluid which keeps the baby warm and it also have the placenta which the baby feeds from
Maureen
atom, molecules, organelle, cell, tissue, organ, organ system
Cheila Reply
sub atom atom molecular molecules and cells.
Advertus
cells structural level.
Advertus
what is microorganisms I am a laboratory student.
Advertus
a small organism
Rahbliss
small organism that can only be seen under a microscope
Maureen
i am just interested to be part of ,to learn
mar
explain why is it that old peoples as from the age of 60 usually have eye problems?
Kenn Reply
most old people suffere eye problems.because of short sight where individuals with this kind of problems see only near objects clearly but not distance objects, this is cause by elongated eyeball so light from distance is focus infront the retina so the image on the retina is blurred .
Munyah
plasma DNA cytoplasm Ribosome
Pearl Reply
cell, tissue,organ, organ systems,organism
Pearl Reply
cell is the build block of Life
Pearl
also a smallest unit of life
Frankline
sure..
Pearl
consistsof cytoplsm enclosed with in a membrane which contains many biomolecules such as proteins and nucleic acids
Frankline
differences in the effects of infection by HIV and influenza A virus on host genetic variability.
Yo Reply
i dont know
Ubah
hiv is direct contact of blood or body fluid and if not treated can break down the immune system faster and lead to acids with complications of pneumonia skin infections inflammation of the brain etc.while influenza A is a air borne virus which can cause the common cold pain fever and can be cured
Maureen
A.I.D.S
Maureen
suggest bioingormatics research article plz
peermehirali
what makes the heart to pumps blood?
Jamer Reply
sa node
Ubah
i do think its the nerve tranmission to the brain
Frankline
The contracting and relaxing of the atria and vertricles but the electrical system of the heart is what makes this possible.
keynia
yes which is called autorhymicity
Maureen
Yes,,by sucking blood leading to the weakening of cells,and finally it will be destroyed....
R0se
adrenoline action in brains
Frankline Reply
please describe the human heart brefly
Shah Reply
the size of the heart is like a fist. it has four chambers. the left and right upper atrium which push blood in the lower left and right ventricles which in turns pump blood to the lungs or the rest of the body.
Maureen
how do u prove it
Frankline
Maureen is correct ,
Davis
right
Kenn
right
Ubah
hi
horyaal
mxaa lahayaa
horyaal
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?

Ask