Electrostatics
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An electrostatic effect: foam peanuts clinging to a cat's fur due to static electricity. The triboelectric effect causes an electrostatic
charge to build up on the surface of the fur due to the cat's motions. The electric field of the charge causes polarization of the
molecules of the foam due to electrostatic induction, resulting in a slight attraction of the light plastic pieces to the charged fur. [1][2][3]
[4]
This effect is also the cause of static cling in clothes.
Electrostatics is a branch of physics that studies electric charges at rest (static electricity).
Since classical times, it has been known that some materials, such as amber, attract lightweight particles
after rubbing. The Greek word for amber, ἤ λεκτρον (ḗ lektron), was thus the source of the word 'electricity'.
Electrostatic phenomena arise from the forces that electric charges exert on each other. Such forces are described
by Coulomb's law.
Even though electrostatically induced forces seem to be rather weak, some electrostatic forces are relatively large.
The force between an electron and a proton, which together make up a hydrogen atom, is about 36 orders of
magnitude stronger than the gravitational force acting between them.
There are many examples of electrostatic phenomena, from those as simple as the attraction of plastic wrap to one's
hand after it is removed from a package, to the apparently spontaneous explosion of grain silos, the damage of
electronic components during manufacturing, and photocopier & laser printer operation. Electrostatics involves the
buildup of charge on the surface of objects due to contact with other surfaces. Although charge exchange happens
whenever any two surfaces contact and separate, the effects of charge exchange are usually noticed only when at
least one of the surfaces has a high resistance to electrical flow, because the charges that transfer are trapped there
for a long enough time for their effects to be observed. These charges then remain on the object until they either bleed
off to ground, or are quickly neutralized by a discharge. The familiar phenomenon of a static "shock" is caused by the
neutralization of charge built up in the body from contact with insulated surfaces.
Coulomb's law[edit]
Main article: Coulomb's law
Coulomb's law states that:
'The magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional
to the product of the magnitudes of charges and inversely proportional to the square of the distance between them.'
The force is along the straight line joining them. If the two charges have the same sign, the electrostatic force between
them is repulsive; if they have different signs, the force between them is attractive.
, If is the distance (in meters) between two charges, then the force (in newtons) between two point charges
and (in coulombs) is:
where ε0 is the vacuum permittivity, or permittivity of free space: [5]
The SI units of ε0 are equivalently A2⋅s4 ⋅kg−1⋅m−3 or C2⋅N−1⋅m−2 or F⋅m−1. The Coulomb constant is:
A single proton has a charge of e, and the electron has a charge of −e, where,
These physical constants (ε0, k0, e) are currently defined so that e is exactly defined, and ε0 and k0 are measured
quantities.
Electric field[edit]
The electrostatic field (lines with arrows) of a nearby positive charge (+) causes the mobile charges in conductive objects to separate
due to electrostatic induction. Negative charges (blue) are attracted and move to the surface of the object facing the external charge.
Positive charges (red) are repelled and move to the surface facing away. These induced surface charges are exactly the right size and
shape so their opposing electric field cancels the electric field of the external charge throughout the interior of the metal. Therefore, the
electrostatic field everywhere inside a conductive object is zero, and the electrostatic potential is constant.
The electric field, , in units of newtons per coulomb or volts per meter, is a vector field that can be defined
everywhere, except at the location of point charges (where it diverges to infinity). [6] It is defined as the electrostatic
Jump to navigationJump to search
An electrostatic effect: foam peanuts clinging to a cat's fur due to static electricity. The triboelectric effect causes an electrostatic
charge to build up on the surface of the fur due to the cat's motions. The electric field of the charge causes polarization of the
molecules of the foam due to electrostatic induction, resulting in a slight attraction of the light plastic pieces to the charged fur. [1][2][3]
[4]
This effect is also the cause of static cling in clothes.
Electrostatics is a branch of physics that studies electric charges at rest (static electricity).
Since classical times, it has been known that some materials, such as amber, attract lightweight particles
after rubbing. The Greek word for amber, ἤ λεκτρον (ḗ lektron), was thus the source of the word 'electricity'.
Electrostatic phenomena arise from the forces that electric charges exert on each other. Such forces are described
by Coulomb's law.
Even though electrostatically induced forces seem to be rather weak, some electrostatic forces are relatively large.
The force between an electron and a proton, which together make up a hydrogen atom, is about 36 orders of
magnitude stronger than the gravitational force acting between them.
There are many examples of electrostatic phenomena, from those as simple as the attraction of plastic wrap to one's
hand after it is removed from a package, to the apparently spontaneous explosion of grain silos, the damage of
electronic components during manufacturing, and photocopier & laser printer operation. Electrostatics involves the
buildup of charge on the surface of objects due to contact with other surfaces. Although charge exchange happens
whenever any two surfaces contact and separate, the effects of charge exchange are usually noticed only when at
least one of the surfaces has a high resistance to electrical flow, because the charges that transfer are trapped there
for a long enough time for their effects to be observed. These charges then remain on the object until they either bleed
off to ground, or are quickly neutralized by a discharge. The familiar phenomenon of a static "shock" is caused by the
neutralization of charge built up in the body from contact with insulated surfaces.
Coulomb's law[edit]
Main article: Coulomb's law
Coulomb's law states that:
'The magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional
to the product of the magnitudes of charges and inversely proportional to the square of the distance between them.'
The force is along the straight line joining them. If the two charges have the same sign, the electrostatic force between
them is repulsive; if they have different signs, the force between them is attractive.
, If is the distance (in meters) between two charges, then the force (in newtons) between two point charges
and (in coulombs) is:
where ε0 is the vacuum permittivity, or permittivity of free space: [5]
The SI units of ε0 are equivalently A2⋅s4 ⋅kg−1⋅m−3 or C2⋅N−1⋅m−2 or F⋅m−1. The Coulomb constant is:
A single proton has a charge of e, and the electron has a charge of −e, where,
These physical constants (ε0, k0, e) are currently defined so that e is exactly defined, and ε0 and k0 are measured
quantities.
Electric field[edit]
The electrostatic field (lines with arrows) of a nearby positive charge (+) causes the mobile charges in conductive objects to separate
due to electrostatic induction. Negative charges (blue) are attracted and move to the surface of the object facing the external charge.
Positive charges (red) are repelled and move to the surface facing away. These induced surface charges are exactly the right size and
shape so their opposing electric field cancels the electric field of the external charge throughout the interior of the metal. Therefore, the
electrostatic field everywhere inside a conductive object is zero, and the electrostatic potential is constant.
The electric field, , in units of newtons per coulomb or volts per meter, is a vector field that can be defined
everywhere, except at the location of point charges (where it diverges to infinity). [6] It is defined as the electrostatic
