Chapter 22: Electrostatics Flashcards
Electricity is the name given to a wide range of electrical phenomena such as:
1) Lightning
2) Spark when we strike a match
3) What holds atoms together
Electrostatics involves electric charges
1) The forces between them
2) The aura that surrounds them
3) Their behavior in materials
Central rule of electricity
Opposite charges attract one another, like charges repel
An electric charge is
The quantity of unbalanced electricity with symbols of q or Q
Electric charges have three difference characteristics includes:
1) Protons (+e)
2) Electrons (-e)
3) Neutrons (-/+e)
Protons (+e), particles with
Positive electric charge, and repel positives but attract negatives
Electron (-e) was the
Negative electric charges and repel negatives, but attract positives
Neutral (+/- e) was the
Neutral electric charge
Atom charged nucleus surrounded by
Negatively charged electrons
Every electron in any atom has the same
Charge and mass
Protons and neutrons compose the nucleus
1) 1800 times more massive than electrons
2) Proton carries amount of positive charge equal to the negative charge of electrons
3) Neutral have slightly more mass than protons and no net charge
Atoms usually have as many electrons as
Protons so the atom has zero net charge
Positive ions (cation)
Atom losing one or more electrons has positive net charge
Negative ions (anion)
Atom againing one or more electrons has negative net charge
Innermost attracted very strongly to
Oppositively charged atomic nucleus
Outermost attracted loosely and can be
Easily dislodged
When rubbing a comb through your hair, electrons transfer from
Your hair to the comb
Your hair has a deficiency of electrons
Positively charged
When rubbing a glass rod with silk, electrons transfer from
The rod onto the silk and the rod becomes positively charged
When you brush your hair and scrape electrons from the comb, the charge of your hair is
Negative, because if the electrons were scraped off your hair onto the brush, your hair would have a positive charge
Conservation of energy, in any charging process, no electrons are
Created or destroyed
Electrons are simply transferred from
One material to another
Conductors share the
Charged
Coulomb’s law (Newton’s Law of gravitation): Relationship among electrical force, charge, and distance discovered by
Charles Coulomb in the 18th century
For a pair of charged objects that are much smaller than the distance between them, the force between them varies
Directly as the product of their charges, and inversely as the square of the separation distance
If the charges are alike in sign, the force is
Repelling
If the charges have opposite sign, the force is
Attractive
According to Coulomb’s law, a pair of particles that are placed twice as far apart will experience forces that are
One quarter as strong
Difference between gravitational and electrical forces
1) Gravitational forces (weak) are only attractive
2) Electrical forces (strong) may be either attractive or repulsive
Conductors: Material in which one or more of the electrons in the outer shell of its atoms are not anchored to
The nuclei of particular atoms but are free to wander in the material
Insulators: Materials in which electrons are tightly bound and belong to particular atoms and are not free to
Wander about among other atoms in the material, preventing them from flowing
Conduction charged by
Friction and contract
Electrons transfer from
One material to another via touch
When a negatively charged rod is placed in contact with a neutral object, some electrons will
Move to the neutral object
If you bring a charged object near a conducting surface, electrons are made to:
Move in the surface material, even without physical contact
Negative charge at the bottom of the cloud induces a
Positive charge on the building belows
An electron buzzing around the atomic nucleus produces
An electron cloud
The center of the negative cloud normally coincides with
The center of the positive nucleus in an atom
When an external negative charge is brought nearby to the right, the electron cloud is
Distorted so that the centers of negative and positive charge no longer coincide and the atom is now electrically polarized
If the rod has negative charge, then the positive parts of the atoms or molecules are
Tugged toward the rod, and the negative parts are pushed away from the rod
The relative orientations of the positive and negative parts of the atoms or molecules align, and the materials becomes
Electrically polarized
Rub an inflated balloon on your hair, and it becomes
Charged
Place the balloon against the wall, and it
Stick and this is because the charge on the balloon induces an opposite surface charge on the wall
Many molecules (H20) for example are
Electrically polarized in their normal states
The distribution of electric charge is
Not perfectly even there is a little more negative charge on one side of the molecule than the other such molecules are said to be “electric dipoles”
The electric fields fill the space surrounding an
Electric charge (an energetic aura)
The electric field is a
Vector (has a magnitude and a direction)
The electric field is mediates the electric force felt by
Other particles
The electric field has unit of force per charge like:
Newton per coulomb
The electric field has a magnitude which diminishes as
The inverse square of the distance from the particle creating the field
Analogous to gravitational field
Gravitational and electrical forces
A gravitational force holds the satellite in
Orbit about the planet
An electric force holds the electron in orbit about
The proton and in both case, there is no contact between the bodies (force fields)
Positive charge has an E-field pointing radially
Outward
Negative charge has an E-field pointing radially
Inward
The force felt by a particle in an electrical field is in the direction of the field for
A positive charge and opposite the field direction for a negative charge
Electric potential energy (Units: Joules): Energy possessed by a charged particle due to its
Location in an electric field
Work is required to push a charged particle against
The electric field of a charged body
The spring has more mechanical PE when
Compressed
The charged particle similarly has more EPE when pushed closer to
The charged sphere
The increased PE is the result of
Work input
Electric potential (voltage) possessed by
A charge particle due to its location
Electric potential voltage may be called
Voltage potential energy per charge
High voltage can induce low electric potential energy for a
Small amount of charge
High voltage induces high electric potential energy for
Lots of charge
A common laboratory device for producing high voltages and creating static electricity is
The Van de Graaff generator
The base of the generator has a
Voltage source, a motor driven roller and metal points
The electric field inside the metal sphere is
Always zero, so the charges that leak off the belt are not repelled by the charge stored on the outside of the sphere
