3. TABLE OF CONTENTS
• What is Electrostatics?
• Coulomb’s Law of Electrostatics
• Electric field
• Positively Charged Particles
• Negatively Charged Particles
• Neutral Particles
• Electrostatics Examples
• The Van de Graaff Generator
• Laser Printers
• Ink Jet Printers and Electrostatic Painting
4. WHAT IS ELECTROSTATICS?
• Electrostatics is a branch of physics that deals with the
phenomena and properties of stationary or slow-moving
electric charges. Electrostatic phenomena arise from the
forces that electric charges exert on each other and are
described by Coulomb’s law. Even though electrostatically
induced forces seem to be relatively weak.
5. COULOMB’S LAW OF ELECTROSTATICS
• We begin with the magnitude of the electrostatic force
between two point charges q and Q . It is convenient to
label one of these charges, q , as a test charge, and
call Q a source charge. As we develop the theory, more
source charges will be added. If r is the distance between
two charges, then the force of electrostatic formula is:
6. ELECTRIC FIELD
• Electric field lines help visualize the electric field.
Field lines begin on a positive charge and terminate on a
negative charge. Electric field lines are parallel to the
direction of the electric field, and the density of these
field lines is a measure of the magnitude of the electric
field at any given point.
• We show charge with “q” or “Q,” and the smallest unit charge
is 1.6021 x 10-19 Coulomb (C). One electron and a proton have
the same amount of charge
7. POSITIVELY CHARGED PARTICLES
• In these particles, the numbers of positive ions are larger
than the numbers of negative ions. This means the numbers of
protons are larger than the number of electrons. To
neutralize positively charged particles, electrons from the
surroundings come to this particle until the number of
protons and electrons becomes equal.
8. NEGATIVELY CHARGED PARTICLES
• Similarly numbers of electrons are larger than the number of
protons. To neutralize negatively charged particles, since
protons cannot move and cannot come to negatively charged
particles, electrons move to the ground or any other
9. NEUTRAL PARTICLES
• Neutral particles include equal numbers of protons and
electrons. They have both protons, neutrons and electrons;
however, the numbers of positive ions equal the numbers of
10. ELECTROSTATICS EXAMPLES
• There are many examples of electrostatic phenomena:
• The attraction of the plastic wrap to your hand after you
remove it from a package.
• The attraction of paper to a charged scale.
• The apparently spontaneous explosion of grain silos.
• The damage of electronic components during manufacturing.
• Photocopier and laser printer operation.
11. THE VAN DE GRAAFF GENERATOR
• A Van de Graaff generator is an electrostatic generator which uses a moving belt
to accumulate electric charge on a hollow metal globe on the top of an insulated
column, creating very high electric potentials. It produces very high voltage direct
current (DC) electricity at low current levels.
12. VAN DE GRAAFF GENERATOR
Figure 1. Schematic of Van de Graaff generator. A battery
(A) supplies excess positive charge to a pointed
conductor, the points of which spray the charge onto a
moving insulating belt near the bottom. The pointed
conductor (B) on top in the large sphere picks up the
charge. (The induced electric field at the points is so large
that it removes the charge from the belt.) This can be
done because the charge does not remain inside the
conducting sphere but moves to its outside surface. An ion
source inside the sphere produces positive ions, which
are accelerated away from the positive sphere to high
13. LASER PRINTERS
• A laser printer is a popular type of computer printer that uses a non-impact
photocopier technology where there are no keys striking the paper. When a
document is sent to the printer, a laser beam "draws" the document on a
selenium-coated drum using electrical charges.
14. Figure 2. In a laser printer, a laser
beam is scanned across a
photoconducting drum, leaving a
positive charge image. The other steps
for charging the drum and transferring
the image to paper are the same as in
xerography. Laser light can be very
precisely controlled, enabling laser
printers to produce high-quality
15. INK JET PRINTERS AND ELECTROSTATIC PAINTING
• The nozzle of an ink-jet printer produces small ink droplets, which are sprayed
with electrostatic charge. Various computer-driven devices are then used to direct
the droplets to the correct positions on a page. Electrostatic painting employs
electrostatic charge to spray paint onto odd-shaped surfaces.
16. Figure 4. The nozzle of an ink-jet printer
produces small ink droplets, which are
sprayed with electrostatic charge.
Various computer-driven devices are
then used to direct the droplets to the
correct positions on a page.
• xerography, Image-forming process that relies on a photoconductive substance
whose electrical resistance decreases when light falls on it. Xerography is the
basis of the most widely used document-copying machines (see photocopier).
The process was invented in the 1930s by U.S. physicist Chester F.
18. Figure 2. Xerography is a dry copying
process based on electrostatics. The
major steps in the process are the
charging of the photoconducting drum,
transfer of an image creating a positive
charge duplicate, attraction of toner to
the charged parts of the drum, and
transfer of toner to the paper. Not
shown are heat treatment of the paper
and cleansing of the drum for the next