Download Section 16.1: Electric Charge and Force

Electricity

Charged Objects:
◦ Electrostatics: the study of electrical
charges that can be collected and
held in one place.
◦ Static electricity: electricity caused by
friction.
 Ex: Rubbing shoes on dry carpet.

Electric Charge:
◦ Consider the following example…
 You place two pieces of tape next to
each other onto a table.
 What happens when either is near my
finger?
 What happens when both are near each
other?
 What can you conclude about the
charge on each object?

Electric Charge:
◦ Consider another example…
 You place two pieces of tape onto a
table, one on top of each other.
 What happens when either is near my
finger?
 What happens when both are near each
other?
 What can you conclude about the
charge on each object?

Electric Charge:
◦ Consider another example…
 You place two pieces of tape onto a
table, one on top of each other.
 What general rules can you come up
with to explain the observations you
just made about both scenarios?

Electric Charge:
◦ When concerning electrically charged
substances, there are two rules that
must be obeyed…
 Opposite charges attract.
 Like charges repel.

Electric Charge:
◦ All matter is made of atoms, which
consist of protons, neutrons, and
electrons.
 Each of these subatomic particles has
its own characteristic charge…
 Protons (+), neutrons (0), and electrons
(-).

While referencing specific content in
the notes, explain how you
determine the charge of a particle
that has 13 protons, 22 neutrons,
and 11 electrons.

The term integer in math is defined as “a
member of the set of positive whole
numbers {1,2,3,…}, a member of the set
of negative whole numbers {-1,-2,-3,…}
and zero”. While referencing specific
content in the notes AND the definition
of integers provided above, propose an
explanation as to why you should never
expect to have a charged atom that is
anything other than an integer.

Electric Charge:
◦ All matter is made of atoms, which
consist of protons, neutrons, and
electrons.
 Each of these subatomic particles has
its own characteristic charge…
 If the atom has more electrons than
protons then the sample is negatively
charged.

Electric Charge:
◦ All matter is made of atoms, which
consist of protons, neutrons, and
electrons.
 Each of these subatomic particles has
its own characteristic charge…
 If the atom has less electrons than
protons then the sample is positively
charged.

Electric Charge:
◦ All matter is made of atoms, which
consist of protons, neutrons, and
electrons.
 Each of these subatomic particles has
its own characteristic charge…
 Remember we can’t change the number
of protons, only the number of
electrons.

Ions are atoms of various elements that are either
positively or negatively charged. As we well know
(or least should at this point), atoms gain or lose
enough electrons so as to have the same number
of electrons as the noble gas closest to it in terms
of atomic number. This is the reason that the Ca
atom will lose 2 electrons because it typically has
20 electrons where the noble gas closest to it, Ar,
has 18 electrons. Now, while citing specific
content in the passage above AND in your notes,
identify whether the ion of Cl will be either
negative or positive.

Ions are atoms of various elements that are either
positively or negatively charged. As we well know
(or least should at this point), atoms gain or lose
enough electrons so as to have the same number of
electrons as the noble gas closest to it in terms of
atomic number. This is the reason that the Ca atom
will lose 2 electrons because it typically has 20
electrons where the noble gas closest to it, Ar, has
18 electrons. Now, while citing specific content in
the passage above AND in your notes, identify why
the charge of an ion of Al will be a +3.

Conductors and Insulators:
◦ Electric current is the flow of
electrical charge.
◦ Since electrons are much easier to
remove from an atom than protons,
then electric current is essentially the
flow of electrons.

Conductors and Insulators:
◦ Conductor: materials that very poorly
restrict charge flow or electric
current.
 Allow for relatively easy, free-flowing
electrons.
 Examples of conductors…
 Metals.

Conductors and Insulators:
◦ Insulator: materials that restrict charge
flow or electric current.
 Examples of insulators…
 Wood, glass, silk, and plastics.
 Electric cords are constructed with
copper wires coated in plastic to
eliminate energy waste, promote safety
from electrostatic discharge (shock), and
reduce the potential for starting fire.

The Electrostatic Force:
◦ Electrostatic force: the push or pull
exerted on an object as a result of
another’s charge.
 Can be either attractive or repulsive.
 Dependent on two variables…
 The size of the charge on both objects.
 The greater the charge the greater the
electrostatic force.

The Electrostatic Force:
◦ Electrostatic force: the push or pull
exerted on an object as a result of
another’s charge.
 Can be either attractive or repulsive.
 Dependent on two variables…
 The distance between the two objects.
 The greater the distance between the
two objects, the smaller the force
between them.

While citing specific content found in
the notes AND citing specific evidence
found in the picture below, identify
which case would result in the largest
electrostatic attractive force.

While citing specific content found in
the notes AND citing specific evidence
found in the picture below, identify
which case would result in the largest
electrostatic attractive force.

The Electric Field:
◦ When dealing with charged objects, it
is important to consider the
hypothetical situation involving only
one charged object.
 If there were only one charged object,
would there be an electrostatic force
exerted by the object?
 The answer lies in a theoretical concept
called the electric field.

The Electric Field:
◦ Electric field: a region of space
around any charged body that
predicts the affects of placing
another charged object is placed in
said space.
 To represent this field we employ the
use of field lines.

The Electric Field:
◦ Electric field: a region of space
around any charged body that
predicts the affects of placing
another charged object in said space.
 The density of the lines, not length,
indicates the relative strength of the
field at that location.

The Electric Field:
◦ Electric field: a region of space around
any charged body that predicts the
affects of placing another charged
object is placed in said space.
 The greater the field strength the more
the object placed in the field is affected.
 The greater the electrostatic force placed
on it.

The Electric Field:
◦ Electric field: a region of space around
any charged body that predicts the
affects of placing another charged
object is placed in said space.
 For positive charges field lines radiate
outward from the source producing the
field.

The Electric Field:
◦ Electric field: a region of space around
any charged body that predicts the
affects of placing another charged
object is placed in said space.
 For negative charges field lines radiate
inward toward the source producing the
field.

Draw the electric field for a +2.0 µC.
◦ What is the direction of the force applied
onto a negatively charged object placed
into the field?
◦ What is the direction of the force applied
onto a positively charged object placed
into the field?

Draw the electric field for a +4.0 µC.

Draw the electric field for a -2.0 µC.
◦ What is the direction of the force applied
onto a negatively charged object placed
into the field?
◦ What is the direction of the force applied
onto a positively charged object placed
into the field?
◦ So, what can you conclude about
positively/negatively charged objects and
the direction of force applied onto them?

If I lift a box up in the air I am doing work
onto it. “Work”, in the science sense can be
defined as a force acting through a
displacement (w = Fd). Because of this action
of work, we are transferring potential (stored)
energy to the box.
◦ The picture on the next slide illustrates a
positively charged object creating an electric
field and a negatively charged object that is
pulled from location A to B. While referencing
the passage above and the picture on the next
slide, identify whether you believe that you can
store electrical energy the same way that you
can gravitational energy.

Is it possible to store electrical energy if
both objects were positively charged?
Explain your rationale.

Voltage and Current:
◦ Just like gravity, systems involving
charged bodies also have a potential
energy.
 Gravitational potential energy is defined
as PE = mgh or PE = Fgh.
 Thus, the larger the weight force or
distance between the object and the Earth
the greater the potential energy of the
object.

Voltage and Current:
◦ Just like gravity, systems involving
charged bodies also have a potential
energy.
 Electrical potential energy: the energy
stored in an electrical system as a
result of its position and charge.
 Unlike gravitational potential energy,
electric potential energy can be
attractive and repulsive.

Voltage and Current:
◦ Just like gravity, systems involving
charged bodies also have a potential
energy.
 Electrical potential energy:
 Unlike gravitational potential energy,
electric potential energy can be
attractive and repulsive.
 This makes electric potential energy
somewhat different…

Voltage and Current:
◦ Just like gravity, systems involving
charged bodies also have a potential
energy.
 Electrical potential energy:
 Consider the two following examples…
 Two unlike charges separated by a
distance.
 So…

Voltage and Current:
◦ Just like gravity, systems involving
charged bodies also have a potential
energy.
 Electrical potential energy:
 Consider the two following examples…
 Two like charges separated by a
distance.
 So…

While referencing specific content in your notes
AND citing evidence found in the picture below,
which of the following locations, “A” or “B”, will
be of greatest electric potential? Hint…the
object at either point is a negatively charged
object.

Which of the following cases will produce
the greatest electric potential? Hint…in
both cases the two charged objects are
separated by an equal distance of “r”.
Provide justification for your answer.

Voltage and Current:
◦ Current (I): the flow of charge.
 Analogous to water flowing through a
pipe.
 Measured in amperes or amps (A).

Voltage and Current:
◦ Now, imagine a ball on a hill…
 Because it is at the top, it has potential
energy.
 This means that work can be done onto
it, which means that the ball will begin
accelerating down the hill.
 This accumulation of speed will occur
until the gravitational potential energy
reaches a minimum.
 The same thing happens for electrical
systems.

Voltage and Current:
◦ Now, imagine a ball on a hill…
 This accumulation of speed will occur
until the gravitational potential energy
reaches a minimum.
 Just as the ball moves because there is a
difference in gravitational potentials,
charge, and thus current, will flow in
electrical systems.
 This will always occur from high electric
potential to low electric potential – same
as gravitational potential energy.

Voltage and Current:
◦ Now, imagine a ball on a hill…
 This will always occur from high
electric potential to low electric
potential – same as gravitational
potential energy.
 This difference in electric potential
energies is referred to as a potential
difference (V).
 This is what drives current.

Voltage and Current:
◦ Now, imagine a ball on a hill…
 This will always occur from high
electric potential to low electric
potential – same as gravitational
potential energy.
 This difference in electric potential
energies is referred to as a potential
difference (V).
 Measured in volts (V).

The picture below illustrates two metal
spheres of differing charges. The
outcome of touching these two spheres
is also illustrated. As you can see
electrons are moving from sphere 1 to
sphere 2. As already defined in the
notes, the movement of electrons is
called current and is measured in
amperes (A). While referencing electric
potentials AND the picture below,
explain why electrons move from
sphere 1 to sphere 2.

Voltage and Current:
◦ Electrical Resistance:
 Just as water encounters friction
between itself and the pipe it is
traveling through, current also
encounters a special type of friction
called resistance.
 Resistance: the slowing or restricting of
charge flow.
 Created because not even metals are
perfect conductors.

Voltage and Current:
◦ Electrical Resistance:
 Just as water encounters friction between
itself and the pipe it is traveling through,
current also encounters a special type of
friction called resistance.
 Resistance: the slowing or restricting of
charge flow.
 Without resistance current would occur
instantaneous and thus no potential
difference would exist and thus no
current.

Voltage and Current:
◦ Electrical Resistance:
 Just as water encounters friction
between itself and the pipe it is
traveling through, current also
encounters a special type of friction
called resistance.
 Resistance: the slowing or restricting of
charge flow.
 A resistor is a substance that has a
specified amount of resistance.

Voltage and Current:
◦ Electrical Resistance:
 Just as water encounters friction
between itself and the pipe it is
traveling through, current also
encounters a special type of friction
called resistance.
 Resistance: the slowing or restricting of
charge flow.
 Measured in ohms (Ω).

Voltage and Current:
◦ Electrical Resistance:
 Just as water encounters friction
between itself and the pipe it is
traveling through, current also
encounters a special type of friction
called resistance.
 Resistance: the slowing or restricting of
charge flow.
R = V/I

As stated on page 6 of your notes, an
electric potential difference (V) is “what
drives electric current (I)”. The greater this
potential difference in electric energies
becomes, the greater the value of the
current. While referencing the passage
above AND specific evidence located on the
graphs presented on the next slide, explain
which graph is CORRECTLY illustrating the
relationship between potential difference
and current.

An experiment is conducted by attaching a
source of voltage through wires constructed
of various materials. Current is measured
and the results are presented on the graph
located on the next slide. While citing
specific evidence found in the graph on the
next slide AND referencing your notes,
identify through which material will the
current encounter the most resistance.
The Current Passing Through Various Materials as a
Result of Varying Potential Differences
14.0
12.0
Material A
Material B
Current (I)
10.0
Material C
Material D
8.0
6.0
4.0
2.0
0.0
0.0
2.0
4.0
6.0
Potential Difference (V)
8.0
10.0
12.0


As stated earlier in the notes, the term
“resistance” is used to describe the frictionlike properties of a conductor. Essentially,
resistance reduces electric current.
While citing the passage above, explain how
the equation below is an adequate
mathematical description of electrical
resistance.
R = V/I



Find the resistance of a portable lantern
that uses 24 V power supply and draws a
current of 0.80 A.
The current in a handheld video game is
0.50 A. If the resistance of the game’s
circuitry is 12 Ω, what is the voltage
produced by the battery?
A 1.5 V battery is connected to a small
light bulb with a resistance of 3.5 Ω.
What is the current in the bulb?

Common resistors…

What is the amount of resistance of
the first four resistors found in the
picture below?

What are Circuits?
◦ A typical electrical circuit contains
each of the following…
 Wires.
 A bulb or some other resistor.
 Source of emf (electromotive force).
 Example: battery, outlet, generator, etc.

What are Circuits?

Other circuit symbols…

What are Circuits?
◦ Remember, in order for a continuous
current to flow, an electric potential
must be maintained at all times.
 This is why a closed-loop (continuous
path from terminal to terminal) of wire
and components must be used.
 An open-loop would lead to a build-up
of charge in one location leading to a
decrease in potential difference.
 Stops charge flow.

Diagramming Circuits:
1. Draw the symbol for a source of
Emf – usually a battery.
 Positive terminal on top.
2. Draw a wire coming out of the
positive terminal.
 When you reach a resistor or
other device, draw the symbol
for it.

Diagramming Circuits:
3. Place a junction “point” anywhere
that there are two possible
current paths.
 Place another where the paths
reconnect.
4. Continue until you reach the
negative terminal of the battery.

Draw an electrical circuit that contains
each of the components in order…
◦ 9.0 V battery, followed by a 30 Ω
resistor, and finally followed by an open
switch.

Draw a diagram that contains a 6.0 V
battery connected to a light bulb.
◦ Include in your diagram a voltmeter and
an ammeter.

Series and Parallel Circuits:
◦ Series: a single pathway for charge
flow.
 You should be able to trace the path
of charge flow with your finger
without ever having to pick it up.
 Just like a garden hose, a series circuit
will have the same current at any one
location in the circuit.

Series and Parallel Circuits:
◦ Series: a single pathway for charge
flow.
 Because of V = IR and resistance
being different for each component in
a series circuit, the voltage across
each component can be unique.
 These voltages however, will add up to
the total the voltage of the battery.

Series and Parallel Circuits:
◦ Series: a single pathway for charge
flow.
 Since this circuit type offers only one
pathway of charge flow, removing one
component will result in a failure of
the circuit.
 Results in an open-loop construction.

Series and Parallel Circuits:
◦ Parallel: a circuit that offers multiple
pathways of charge flow.
 You will NOT be able to trace the path of
charge flow with your finger without ever
having to pick it up.
 Operates more like a 3-way garden hose
splitter than a single garden hose.
 Each path will have its own unique current
based on resistance of the path.

Series and Parallel Circuits:
◦ Parallel: a circuit that offers multiple
pathways of charge flow.
 Operates more like a 3-way garden hose
splitter than a single garden hose.
 The sum of all currents coming out of the
pathways however, equal the total current
coming into the circuit.

Series and Parallel Circuits:
◦ Parallel: a circuit that offers multiple
pathways of charge flow.
 Operates more like a 3-way garden hose
splitter than a single garden hose.
 This splitting of current is the reason for
lights dimming when turning on another
device at home.
 Lights in series won’t dim because
current isn’t split and thus reduced.
 Remember…P = IV and P = I2R.

Series and Parallel Circuits:
◦ Parallel: a circuit that offers multiple
pathways of charge flow.
 As a result of offering multiple paths for
charge flow, this type of circuit
construction allows for one or more
components to be removed, yet allow for
all other components to be functional.
 This is the reason why we can have
multiple devises plugged into the same
outlet.

Series and Parallel Circuits:
◦ Parallel: a circuit that offers multiple
pathways of charge flow.
 As a result of offering multiple paths for
charge flow, this type of circuit
construction allows for one component
to be removed, yet allow for all other
components to be functional.
 When you unplug one it doesn’t mean
that all other devices fail.

Series and Parallel Circuits:
◦ Parallel: a circuit that offers multiple
pathways of charge flow.
 Even though each pathway may have
its own current, the potential
difference across each pathway is the
same.

Which of the following pictures below
is in series? Parallel?

Which of the following pictures below
is in series? Parallel?

Using the picture below, draw lines, which will
represent wires, in such a fashion to put the
bulbs in series. Parallel.

Electric Power and Electrical Energy:
◦ Recall the ball and hill example…
 As the ball traveled down the hill (high
gravitational potential energy to low
gravitational potential energy), much of it’s
potential energy is converted into kinetic
energy.
 The same happens to electrical systems.
 Energy lost when the charge flows from high
electric potential to low electric potential is
converted into other forms, such as light,
sound, or heat.

Electric Power and Electrical Energy:
◦ Recall the ball and hill example…
 As the ball traveled down the hill (high
gravitational potential energy to low
gravitational potential energy), much
of it’s potential energy is converted
into kinetic energy.
 This is the reason why resistors heat as
current travels through them.

Electric Power and Electrical Energy:
◦ Recall the ball and hill example…
 As the ball traveled down the hill (high
gravitational potential energy to low
gravitational potential energy), much of
it’s potential energy is converted into
kinetic energy.
 The rate at which this electric energy is
converted to some other form is…
P = IV and P = I2R

The Kilowatt-Hour:
◦ Energy companies vs. “power”
companies.
 You pay for electrical energy usage not
power.
◦ Kilowatt-hour (kWh): equal to 1000
watts delivered continuously for 3600
seconds.

Fuses and Circuit Breakers:
◦ As you have already learned, as current
meets a resistance, energy is pulled out
of the electric circuit and converted
into a different form like heat (P = I2R).
 Wiring, although conductor, does carry a
small amount of resistance.
 So, when you plug too many devices into
an outlet you increase the risk of fire.

Fuses and Circuit Breakers:
◦ As you have already learned, as current
meets a resistance energy is pulled out
of the electric circuit and converted
into a different form like heat (P = I2R).
 Wiring, although conductive, does carry
a small amount of resistance.
 As a result, safeguards like fuses and
circuit breakers are placed into home
wiring to protect against electrical fires.

Fuses and Circuit Breakers:
◦ Fuses: a devise consisting of a thin
ribbon of wire with a low melting point.
 These are placed into the circuit so that
if too much current is passing through
the wires, the ribbon melts, creating an
open-loop.
 Referred to as a “blown fuse”.
 Discontinues charge flow until fuse is
replaced.

Fuses and Circuit Breakers:
◦ Circuit breakers: a switch that opens a
circuit automatically when the current
exceeds a certain value.
 Meets newer electrical code.
 Are also used to prevent electrical fire.
 Resettable.