Chapter 19 Flashcards
Types of Charges
They are called positive and negative
Named by Benjamin Franklin
Like vs Opposite charge
Like charges repel and unlike charges attract one another
Electric charge is always _____
conserved
Charge is not created, only ________
exchanged
Objects become charged because ______
negative charge is transferred from one
object to another
Charge is quantized
All charge is a multiple of a fundamental unit of charge, symbolized by e,
with the value of
e = 1.6 x 10-19 C
o Quarks are the exception
o Electrons have a charge of –e
o Protons have a charge of +e
o The SI unit of charge is the Coulomb (C)
Conductors
are materials in which the electric charges move freely in response to an electric force
o Copper, aluminum and silver are good conductors
o When a conductor is charged in a small region, the charge readily distributes itself over the entire surface of the material
Insulators
are materials in which electric charges do not move freely
o Glass and rubber are examples of insulators
o When insulators are charged by rubbing, only the rubbed area becomes
charged
o There is no tendency for the charge to move into other regions of the
material
Semiconductors
The characteristics of semiconductors are between
those of insulators and conductors
o Silicon and germanium are examples of semiconductors
Charging by Conduction
A charged object (the rod) is placed in contact with another object (the sphere)
o Some electrons on the rod can move to the sphere
o When the rod is removed, the sphere is left with a charge
o The object being charged is always left with a charge having the same sign as the object doing the charging
Charging by Induction
When an object is connected to a conducting
wire or pipe buried in the earth, it is said to
be grounded
o A negatively charged rubber rod is brought
near an uncharged sphere
o The charges in the sphere are redistributed
o Some of the electrons in the sphere are repelled from the electrons in the rod
o A grounded conducting wire is connected to the sphere
oAllows some of the electrons to move from the sphere to the ground
o The wire to ground is removed, the sphere is left
with an excess of induced positive charge
o Charging by induction requires no contact with the
object inducing the charge
Charge Polarization
The charged object (on the
left) induces charge on the
surface of the insulator
o This realignment of charge on the surface of an insulator is known as polarization
Light: Animation
A charged comb attracts bits of paper due to polarization of the paper
Coulomb’s Law
F = (k |q1||q2|) / (r^2)
ke is called the Coulomb Constant
ke = 8.9875 x 109 N m2/C2
Remember that force is a ____ quantity
vector quantity
Electrostatic Force
o Both are inverse square laws
o The mathematical form of both laws is the same
o Masses replaced by charges
o Electrical forces can be either attractive or
repulsive
o Gravitational forces are always attractive
o Electrostatic force is stronger than the
gravitational force
Coulomb’s Law for Multiple
Charges
o The resultant force on any one charge
equals the vector sum of the forces exerted
by the other individual charges that are
present.
o Remember to add the forces as vectors
If q is positive
charge repels
If q is negative
charge attracts
Electrical Field
E (r on top) = ((F (I on top)) / (q (subscript o) = (K (subscript e) Q) / r^2
Electrical Field SI units are
N / C
The electric field is a _____ _____
vector quantity
The direction of the field is defined to be the
direction of the electric force that would be
exerted on a _______
small positive test charge, qo,
placed at that point
