M.R.RIFAS AHAMEDFACULTY OF GEOMATICS

SABARAGAMUWA UNIVERSITY OF SRILANKA

WHAT IS ELECTRIC CHARGE? Electric charge, basic property of matter carried by

some elementary particles. Electric charge, which can be positive or negative, occurs in discrete natural units and is neither created nor destroyed.

Electric charges are of two general types: positive and negative. Two objects that have an excess of one type of charge exert a force of repulsion on each other when relatively close together. Two objects that have excess opposite charges, one positively charged and the other negatively charged, attract each other when relatively near.

SOURCE>>http://en.wikipedia.org/wiki/Electric_charge 2

CONSERVATION ELECTRIC CHARGE

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CONSEVATION CONT… Mathematically, we can state the law as a

continuity equation:

Q(t) is the quantity of electric charge in a specific volume at time t, Qin is the amount of charge flowing into the volume between time t1 and t2 and Qout is the amount charge flowing out of the volume during the same time period.

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Electrostatics is the study of the effects of stationary charges on each other in their surroundings.

Charges are created by the transfer of electrons to or from one body to another. (Protons are NEVER transferred.)

Objects with equal numbers of protons and electrons are neutral. They have no net charge.Objects with more electrons than protons

are charged negatively

Objects with less electrons than protons are charged positively.

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- +

+ +

- +

--++

- -Likesrepel

Likesrepel

Unlikesattract

Unlikesattract

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6.25 x 10 18electrons1 coulomb

Charge on 1 electron = - 1.6 x 10 –19

coulombsCharge on 1 proton = + 1.6 x 10 –19

coulombs

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SOURCE>>www.slideshare.net

ELECTROSCOPE

An electroscope is an early scientific instrument that is used to detect the presence and magnitude of electric charge on a body. It was the first electrical measuring instrument. 9

METHODS OF CHARGING Objects can be charged by FRICTION OR

RUBBING

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CHARGING CONT… Charging by INDUCTION

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CHARGING BY CONDUCTION

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CHARGING BY GROUNDIND

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In physics, particularly electromagnetism, the Lorentz force is the combination of electric and magnetic force on a point charge due to electro magnetic fields.

If a particle of charge q moves with velocity v in the presence of an electric field E and a magnetic field B, then it will experience a force. (Wikipedia)

The first derivation of the Lorentz force is commonly attributed to Oliver Heaviside in 1889, although other historians suggest an earlier origin in an 1865 paper by James Clerk Maxwell. Hendrik Lorentz derived it a few years after Heaviside

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LORENTZ

*Born 18 July 1853Arnhem, Netherlands*Died 4th February 1928 (aged 74)Haarlem, Netherlands*Nationality Netherlands

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Say a charge Q resides at point r , and is moving at a velocity v.

Somewhere, other charges and currents have generated an electric field E(r ) and magnetic flux density B(r ).

These fields exert a force on charge Q equal to

F =Q {E(r ) + vxB(r )} Here the force due to E(r ) (i.e.,Fe), could

be parallel to velocity vector v.16

For that case, E(r ) will apply a force on the charge in the direction of its velocity. This will speed up (i.e., accelerate) the charge, essentially adding kinetic energy to the charged particle.

Or, the force due to E(r ) could be anti-parallel to velocity vector u. For this case, the electric field E(r ) applies a force on the charge in the opposite direction of its movement. This will slow down the charge, essentially extracting kinetic energy from the charged particle.

vFe

vFe 17

Now, contrast this with the force applied by the magnetic flux density. We know that:

Fm = {vxB(r )}QTherefore, the force Fm is always orthogonal to velocity

vector v

As a result, the force due to the magnetic flux density B(r ) can change the direction of velocity u (i.e., change particle path), but not the magnitude of the velocity v .

In other words, the force Fm neither speeds up or slows down a charged particle, although it will change its direction. As a result, the magnetic flux density B(r ) cannot modify the kinetic energy of the charged particle.

Fmv

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You are all very aware of the practical importance of the Lorentz force law! In fact, you likely observe its effects several times each day. An almost perfect application of the Lorentz

Force Law is the Cathode Ray Tube (CRT)—the device at the heart of every television and computer monitor (or, at least, the non-plasma/LED kind!).

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At the very back of a CRT is an element that is heated to very high temperatures. This hot element begins to “emit” electrons into the vacuum of the CRT.

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THANK YOU…

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