Download Physics 242 2 Electric Charges (1)

Electric Charges
Types and Sources of Electric Charge
Two kinds of electric charge – positive
negative
protons
electrons
Bohr Model of Atom
Quantum Mechanical Model
http://csep10.phys.utk.edu/astr162/lect/light/bohr.html
http://www.physics.ucla.edu/~dauger/orbitals/
Materials with equal numbers of neg. and pos. charge are
said to be electrically neutral.
Electric Charges
Types and Sources of Electric Charge
THANKS BEN!
Ben Franklin actually
did a great deal of
experimentation in the
area of electricity.
However, Ben Franklin worked on the negative and
Positive charges a lot. which we are using till now.
Electric Charges
Properties of Electric Charge
• Charge is quantized.
• Positive and Negative charges have same magnitude
e = p = 1.6 x 10-19 C
SI unit of charge is the Coulomb
• Charge is conserved.
only charge will be transferred, but can not be
destroyed or made.
Electric Charges
Atoms and Materials
Different elements will have different
types of bonds – different strengths.
Classification of Materials
– Conductors, Insulators, Semiconductors
Conductors
Insulators
Electrons are free to move
about the material
Electrons are bound to the atoms
- can’t move (conduct).
Electric Charges
Insulators
Free Standing
Atoms are randomly oriented
Charge does not actually move
In/on the insulator – redistributes.
Polarizes the material.
Electric Current
THE ELECTRIC
BATTERY
• A BATTERY is a
source of electric
energy. A simple
battery contains
two dissimilar
metals,
called
ELECTRODES, and
a solution called
the ELECTROLYTE,
in which the
electrodes are
partially immersed.
ELECTRIC CURRENT
• An electric CURRENT
exists whenever
electric charge flows
through a region, e.g.,
a simple light bulb
circuit. The magnitude
of the current is
measured in AMPERES
(Amps/A), where
• 1 ampere =
1coulomb/second
•
I = q / t.
CONVENTIONAL CURRENT
vs ELECTRON CURRENT
• The direction of
CONVENTIONAL CURRENT is
in the direction in which
positive charge flows. In
gases and liquids both
positive and negative ions
move. Only negative
charges, i.e., electrons, move
through solids and this is
referred to as ELECTRON
CURRENT. For historical
reasons, conventional current
is used in referring to the
direction of electric charge
flow.
OHM'S LAW
• The magnitude of the electric current that flows
through a closed circuit depends directly on the
voltage between the battery terminals and
inversely to the circuit resistance. The
relationship that connects current, voltage and
resistance is known as OHM'S LAW and is written
as follows:
• I = V/R or V = IR
• The current is measured in
amperes, the voltage in volts and
the resistance in ohms ().
Resistors
 Symbol on a schematic
diagram
For the color code, the first
two colors represent the
first two digits in the value
of the resistor, the third
represents the power of ten
that it must be multiplied
by, and the fourth is the
tolerance.
RESISTIVITY
 RESISTIVITY: When electric charge flows through a
circuit it encounters electrical RESISTANCE. The
resistance of a metal conductor or this opposition
property of a conductor is called as resistivity.
ELECTRIC POWER
 The rate at which work is done
to maintain an electric current
in a circuit is termed
ELECTRIC POWER.
 W = QV.
 Work is required to transfer
charge through an electric
circuit. The work required
depends on the amount of
charge transferred through the
circuit and the potential
difference between the
terminals of the battery: