Transcript 1.3 Voltage notes

Chapter 1.3
Notes
Voltage
• Two universal forces in
nature are Gravitational
Force and Electrical
Force.
• They are universal
because each force acts
the same everywhere in
the universe.
• Gravitational Forces
act between two or
more masses.
• Electrical Forces
act between two or
more charges.
• Newton’s Universal Law of
Gravitation: every object in
the universe attracts every
other object with a force
that (for two bodies) is
directly proportional to the
mass of each body and that
is inversely proportional to
the square of the distance
between them.
• The gravitational force
Fg is exerted equally on
both masses but the
direction of the force is
different for both
masses.
• The gravitational force
is always an attractive
force.
• The property of an object
that causes electrical force is
called charge.
• There are two types of
charges; positive and
negative.
• Two objects with the same
charge, both positive or both
negative, repel each other.
• Two objects with opposite
charges attract each other.
• The origin of electric
charge is found in the
atom.
• The nucleus of an
atom contains most
of the mass, in the
neutrons and protons.
• Neutrons have no charge and
so they are neutral.
• Protons have a positive charge.
• The nucleus is surrounded by a
cloud of electrons.
• Electrons have a negative
charge.
• The charge of the electron is
equal to the charge of the
proton.
• The force of attraction between
the proton and electron is what
keeps the electron bound to the
nucleus.
• A normal atom has no charge,
since it has an equal amount of
electrons and protons.
• You can transfer charge from
one object to another because
the outermost electrons in the
atoms of some substances are
not tightly bound to the nucleus
and can be removed.
• The net electrical charge in a
system never changes; Principle of
conservation of charge.
• Coulomb’s Law : the electrical
force between two charged bodies
is proportional to the charge on
each body and inversely
proportional to the square of the
distance between them.
• The charge on one electron or
proton is 1.6 x 10 -19 ; This is
called the Elementary Charge.
• A field is an imaginary
construction used by scientists
to help them understand and
predict how forces are
transmitted from one object to
another.
• The direction of a field is shown
with arrows.
• Where the lines are close
together, the magnitude of
the field is high.
• Where the lines are far
apart, the magnitude of the
field is low.
• Field lines can only be
shown in two dimensions,
but true electric fields are
3 Dimensional.
• If you move a charge against
an electric field, you must
exert a force on the charge.
• The charge possesses a
potential because if it is
released, the charge will
accelerate towards its
original position; the field
creates an electric potential
difference.
• In a uniform electric field of
magnitude E, the electrical
potential difference VAB between
the points A and B, separated by
a distance of d is the following:
VAB = E x d
• The unit of measurement for
electric potential difference is
the Volt.
• Electric potential difference is
sometimes simply called
voltage.
• Voltage is the main mover
in electrical systems, like
pressure is the main mover
in fluid systems.
• A flow of charge is called
an electrical current.
• In the electrical system,
current can be maintained
with a battery.
• Electrical systems
contain four major
components:
• Voltage Source – battery
• Conductor – wire
• Load – light bulb
• Control Element - switch
The load in an electrical
system is usually an
appliance or machine such
as an electric motor.
• An electrical conductor is a
material through which
charge can easily flow.
•The control element can
be a switch that turns
the current on or off.
• An electrical
circuit is a closed
path for current
to flow created
by connecting
voltage sources,
conductors,
control elements,
and loads.
• There are two types of current:
Direct and Alternating Current.
• In direct current (DC), the
electric charge flows in one
direction.
• In alternating current (AC), the
electric charge flows back and
forth.
• Batteries produce direct current
and alternators produce
alternating current.
• Another word for a battery
is a cell.
• A cell is a single unit that
contains chemicals.
• As the chemicals react,
electrons are removed
from certain molecules,
leaving behind positively
charged ions.
• The electrons and ions are separated
and this charge separation creates a
voltage.
• Primary cells are batteries designed
for one time use.
• Secondary cells are batteries that
can be recharged.
• In a rechargeable battery, current is
sent through the battery in a reverse
direction, which reverses the
direction of the chemical reaction
and makes the material available
again to produce voltage.
• The voltage output of a
battery is measured between
two terminals.
• These terminals are called
electrodes.
• One electrode is positive and
the other is negative.
• When connected in a
circuit, electrons flow
through the circuit from
the negative to the
positive.
• The negative electrode is
called a cathode.
• The positive electrode is
called the anode.
• Batteries can be added together
in series to produce a higher
voltage.
• Adding cells in series means that
the positive terminal from one
cell is connected to the negative
terminal of another battery.
• In a series circuit, there is only
one path for current.
• In a parallel circuit, there are
many paths for the current to
flow.
Shorthand symbols:
• Battery –
• Light bulb –
• Switch –
• Conductors –
Schematic of a simple circuit:
• An AC voltage source
reverses the positive and
negative terminals many
times per second. A majority
of AC circuits cycle at a rate
of 60 times per second. The
cycling rate is called the
frequency.
• Frequency is measured in
cycles per second, or hertz.