Electrical Force
Unit 1.3
Objectives
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Explain the similarities and differences between
Newton’s law of universal gravitation and Coulomb’s
law.
Explain how the force between two like charges and
the force between two unlike charges are different.
Describe how to create an electric field.
Define electric potential difference or voltage.
Differentiate between AC and DC .
Identify the most common sources of DC voltage.
Describe how to connect DC voltage sources so that
voltages will add.
Gravitational Force
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Newton’s universal law of gravitation
Every object in the universe attracts every other
object with a force that is directly proportional to the
mass of each body and that is inversely proportional
to the square of the distance between them.
Fg= G
m1m2
d2
Where G = 6.67 x 10-11
N m2
kg2
Electric Charge
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Charge – the property of an object that
causes electrical force.
Positive +and Negative - charges exist.
Like charges repel
Unlike charges attract (opposites attract)
Gravity and Electrical Force
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Both are inverse square laws
Both give magnitude of the force one
object exerts on another
Gravitational force is always attractive,
but electrical force can be attractive or
repulsive.
Gravitational forces govern large bodies
Electrical forces govern smaller bodies
Origins of electrical charge
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Anatomy of an atom?
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Protons – Positive charge
Neutrons – Neutral charge
Electrons – Negative charge
Normal atom has no net charge
Electrons can move in some substances
Principle of conservation of charge
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The net electrical charge in an isolated system
never changes. (hair and comb)
Electrical Force
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Charles Coulomb and his law
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The electrical force between two charged bodies is directly
proportional to the charge on each body and inversely
proportional to the square of the distance between them.
charges
FE= K
q1 q2
d2
Where K = 9.0 x 109
Distance
N m2
C2
SI unit = Coulomb (C)
Elementary Charge - Charge on one electron or proton = 1.6 x 10-19 C
Gravitational and Electrical
Fields
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The fields are the space between two
masses or charges and the effects within
them.
Opposite
charges
Positive charge
Negative charge
Like charges
Opposite
plates
Electrical Potential
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When charges are within an electric
field an electrical potential difference is
created.
Volt – unit of measurement for potential
difference. (electrical potential, voltage)
Voltage is the prime mover in electrical
systems (like pressure in fluid system).
Electrical Potential
Flow caused by “potential” difference
Fluid system
Electrical system
Current – Flow
Sources of Difference
A pump is a source of fluid
pressure difference
A battery is a source of
electrical potential
difference
Components of Electrical
Systems
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Voltage source (battery or generator)
Conductors (wires or circuit board)
Load (motor, lights, etc.)
Electrical
circuit
Control element (switch)
Control
Voltage
source
Electrical
Load
AC vs. DC
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Direct Current (DC) – charge flows in
one direction.
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Batteries
Solar Panels
Alternating Current (AC) – charge flows
back and forth.
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Alternators
Generators
Batteries
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Cell – a single unit housing one or more
chemical.
Battery – consist of several cells
How does it work?
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Chemicals react and electrons are removed
creating a potential difference (voltage)
Primary Cells – one time use batteries
(cannot be recharged)
Secondary Cells – Can be recharged
Connecting cells
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Electrodes – the positive and negative
terminals on a battery (cell).
Positive electrode (red) called anode.
Negative electrode (black) called
cathode.
Voltages add when cells are connected
+ +
in series.
Battery
Battery
1.5 v
1.5 v
-
3.0 v
+
A Simple DC Circuit
AC Circuits
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An AC voltage source reverses the
positive and negative terminals many
times per second.
The current flows one direction and
then the other then the other…..
This changing of polarity or cycling is
called frequency, measured in cycles
per second (hertz).
AC vs DC
Where does AC come from?
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The main source of 60hz current comes
from electrical power plants, through
power lines and into your homes.
Generally 110 – 120 volts
Some larger electrical devices need 220
– 240 volts.
Summary
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Newton’s law of universal gravitation and
Coulomb’s law are both inverse squares laws.
The magnitudes of both forces decrease with
the square of the distance between the
masses and the charges.
Atoms are composed of proton, neutrons and
electrons. Protons are positively charged,
electrons are negatively charged, and
neutrons have no charge.
The flow of electrons in an electrical system is
a current.
Unlike charges attract, like charges repel.
Summary (cont.)
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An electric field is a model of the alteration of space
around one or more charges. You can use the field to
predict the force exerted on a charge placed in a the
field.
The potential difference, or voltage, between two
points in a uniform electric field is the product of the
field strength and the distance between the points.
Voltage is the prime mover in electrical systems.
A battery is a source of DC voltage. It can maintain a
current in an electrical circuit.
Batteries or cells can be connected in series to
increase voltage.