This was a group presentation

1. M.R.RIFAS AHAMED
FACULTY OF GEOMATICS
SABARAGAMUWA UNIVERSITY OF SRILANKA

2. 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

3. CONSERVATION ELECTRIC CHARGE
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4. 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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5. 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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6. - +
+ +
- +
--
++
- -Likes
repel
Likes
repel
Unlikes
attract
Unlikes
attract
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7. 7

8. 6.25 x 10 18
electrons
1 coulomb
Charge on 1 electron = - 1.6 x 10 –19
coulombs
Charge on 1 proton = + 1.6 x 10 –19
coulombs
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SOURCE>>www.slideshare.net

9. 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

10. METHODS OF CHARGING
 Objects can be charged by FRICTION OR
RUBBING
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11. CHARGING CONT…
 Charging by INDUCTION
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12. CHARGING BY CONDUCTION
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13. CHARGING BY GROUNDIND
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14.  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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15. LORENTZ
*Born 18 July 1853
Arnhem, Netherlands
*Died 4th February
1928 (aged 74)
Haarlem,
Netherlands
*Nationality
Netherlands
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16.  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.
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17.  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.
v
Fe
v
Fe 17

18.  Now, contrast this with the force applied by the magnetic flux
density. We know that:
Fm = {vxB(r )}Q
Therefore, 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.
Fm
v
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19.  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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20.  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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21. THANK YOU…
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