1/31 do now
• An object is thrown straight upward from
Earth’s surface. Graph the following for the
time that elapses while it is in the air: [Neglect
friction.]
1. a-t
2. v-t
3. d-t
• Due today
– castle learning corrections
– Review packets
• Homework
– 17.1 notes due Monday 2/3
– Castle learning : graphs
• objectives
– Go over midterm
– Go over chapter 7 essays
– Go over chapter 7 project
– Lab – determine power
2/4 do now
• A cart travels with a constant nonzero
acceleration along a straight line. Graph the
following relationships:
1. Acceleration vs. time
2. Velocity vs. time
3. Distance vs. time
Objectives
1. Understand the basic properties of electric
charge.
2. Differentiate between conductors and
insulators.
3. Distinguish between charging by contact and
charging by polarization.
Homework:
Castle learning: you have two days to do. If you
did not finish in time, you can come post session
to make up homework.
Atomic Structure Review
Matter
Within
Atis
Orbiting
the
the
made
center
NUCLEUS
up
theofNUCLEUS
small
each
are two
atom
structures
are
types
isELECTRONS
a NUCLEUS
ofcalled
NUCLEONS
ATOMS
ELECTRONS
NEGATIVE charge
Orbit nucleus
PROTONS
NEUTRONS
POSITIVE CHARGE
NO CHARGE – NEUTRAL
DO NOT MOVE
WITHIN MATTER
DO NOT MOVE
WITHIN MATTER
Charged Objects
Objects are normally electrically NEUTRAL.
They have the same number of protons and electrons
If an object loses electrons, it
becomes
POSITIVELY charged
+
LACK OF ELECTRONS
If an object gains electrons, it
becomes
NEGATIVELY charged
EXCESS ELECTRONS
Only electrons can move, protons and neutrons can not move.
Example
•
1.
2.
3.
4.
Which part of an atom is most likely to be
transferred as a body acquires a static
electric charge?
proton
neutron
electron
positron
Example
•
During a physics lab, a plastic strip was rubbed with cotton
and became positively charged. The correct explanation for
why the plastic strip becomes positively charged is that ...
a. the plastic strip acquired extra protons from the cotton.
b. the plastic strip acquired extra protons during the charging
process.
c. protons were created as the result of the charging process.
d. the plastic strip lost electrons to the cotton during the
charging process.
Charge Interactions
•
•
The electric force is a non-contact force. Any
charged object can exert this force upon other
objects - both charged and uncharged objects.
The nature of the electric force:
1. Opposites attract.
2. likes repel.
The Electric Force and Newton's Third Law
This electric force exerted between two charged objects is a force
in the same sense that friction, tension, gravity and air resistance
are forces. And being a force, the same laws and principles that
describe any force describe the electrical force. One of those laws
was Newton's law of action-reaction. (balloons)
Force of B upon A is the same in
magnitude as Force of A upon B. they
are action and reaction forces.
Force of D upon C is the same in
magnitude as Force of C upon D. they
are action and reaction forces.
Interaction Between Charged and Neutral
Objects
• Any charged object - whether positively charged or
negatively charged - will have an attractive
interaction with a neutral object.
– Positively charged objects and neutral objects
attract each other;
– Negatively charged objects and neutral objects
attract each other.
• Any charged object - plastic, rubber, or aluminum will exert an attractive force upon a neutral object.
And in accordance with Newton's law of actionreaction, the neutral object attracts the charged
object.
Charge detection
• If two objects repel each other…
– one can conclude that both objects are charged and
charged with the same type of charge. One could not
conclude that the balloons are both positively charged or
both negatively charged.
• If two objects attract each other…
– one can conclude that at least one of the objects is
charged. The other object is either neutral or charged with
the opposite type of charge. You cannot draw a conclusion
about which one of the objects is charged or what type of
charge (positive or negative) the charged object possesses.
Example
•
A lightweight sphere hangs by an insulating thread.
A student wishes to determine if the sphere is
neutral or electrostatically charged. She has a
negatively charged hard rubber rod and a positively
charged glass rod. She does not touch the sphere
with the rods, but runs tests by bringing them near
the sphere one at a time. The student notes that
the sphere is attracted to both rods. This test result
shows that the charge on the sphere is
1. positive
2. negative
3. neutral
Example
•
1.
2.
3.
4.
A negatively charged plastic comb is brought
close to, but does not touch, a small piece of
paper. If the comb and the paper are
attracted to each other, the charge on the
paper
may be negative or neutral
may be positive or neutral
must be negative
must be positive
Electric charge is quantized: Millikan
Oil Drop Experiment:
The experiment determined that the charge on an
object is always a multiple of a fundamental unit of
charge, symbolize by e
Definitions
• charge: a fundamental property of matter
– measured in COULOMBS or ELEMENTARY CHARGE
• charge on an object is carried by particles
– Electron
• -1.6 x 10-19 coulombs
• -1e
– Proton
• +1.6 x 10-19 coulombs
• +1e
The units of micro-Coulombs (1 µC = 10-6 C) or nano-Coulombs (nC = 10-9 C)
are more commonly used as the unit of measurement of charge.
Charged Objects
Because objects can only gain or lose electrons, the
only charges that are allowed are multiples of the
ELEMENTARY CHARGE
This plate is neutral – number of protons = number of electrons
If the plate loses three
one electron
two
electrons
electrons
Its charge becomes…
+3
+2
+1ee
Or
-19 Coulombs
+3.2 x 10-19
+4.8
+1.6
Coulombs
The plate has a LACK OF ELECTRONS
+1 Elementary Charges
+2
+3
Charge
Example #1
• An object has three excess electrons.
– What is its “elementary charge”?
-3e
– What is its charge in coulombs?
q = -3e x (1.6 x 10-19 C)/e = -4.8 x 10-19 C
Example #2
• An object has 75 protons and 65 electrons
– What is its “elementary charge”?
+10 e
– What is its charge in coulombs?
q = +10e x (1.6 x 10-19 C)/e = +16 x 10-19 C
Law of Conservation of Charge
• The total amount of charge in a closed
system remains constant – charge is not
created or destroyed, it only moves from one
object to another
• Charge “moves” as a result of ELECTRON
movement ONLY!!!
Example #3
• A metal sphere with two excess electrons touches a
neutral metal sphere and then taken away.
– What do you predict the charge on each sphere will be
after they make contact?
-1e or -1.6 x 10-19 C
– What is the total charge on both spheres after they come
in contact?
-2e or -3.2 x 10-19 C
The TOTAL CHARGE remains the SAME!!!
2/6 do now
• The graph below represents the motion of a car during a
6.0-second time interval.
1. What is the velocity during 4.0 – 6.0 s interval?
2. What is the acceleration during 0.0 – 4.0 s interval?
3. What is the total distance traveled by the car during
this 6.0-second interval?
Objectives
1. Understand the basic properties of electric
charge.
2. Differentiate between conductors and
insulators.
3. Distinguish between charging by contact and
charging by polarization.
Homework:
Castle learning: you have two days to do. If you
did not finish in time, you can come post session
to make up homework.
Recap
1.
2.
3.
4.
5.
What is it that gives objects a charge?
What are some interactions between charges?
What did Miliken’s oil drop experiment determine?
How is it charge measured?
What is the relationship between fundamental charge
and charge in coulombs.
6. What does the Law of Conservation of Charge tell us?
question
• A negative charged sphere is placed near a
neutral sphere. Which graph represents
charge distribution on the neutral sphere?
A.
-
+ - +
C.
-
- +
- +
B.
-
+ + -
D.
-
- - -
Restless Electrons
4.1.2 Transfer of Charge
Conductive Properties of Materials
HIGH CONDUCTIVITY
LOW RESISTIVITY
LOW CONDUCTIVITY
HIGH RESISTIVITY
Good Conductor/
Poor Insulator
Good Insulator/
Poor Conductor
Allows electrons to flow
freely.
Strongly resists flow of
electrons.
The division of materials into the categories of conductors and
insulators is a somewhat artificial division. It is more appropriate
to think of materials as being placed somewhere along a
continuum.
insulators
vs.
Charge on an insulator
will remain at the initial
location of charging.
conductors
charge on a conductor is
quickly distributed across the
entire surface of the object.
Why do think this happens?
The insulating cups are use to prevent charge from escaping to the
surroundings as well as to provide for a convenient handle.
Examples of conductors and insulators
• Examples of conductors
include
– metals,
– aqueous solutions of
salts
– graphite,
– water
– human body.
• Examples of insulators
– plastics,
– Styrofoam,
– paper,
– rubber,
– glass
– dry air.
Human body is a conductor
• Along the continuum of conductors and insulators,
one might find the human body somewhere towards
the conducting side of the middle. When the body
acquires a static charge it has a tendency to distribute
that charge throughout the surface of the body.
• phet
Water is a conductor
• Water, being a conductor, has a tendency to gradually remove
excess charge from objects. Since humidity levels tend to vary
from day to day and season to season, it is expected that electrical
affects (and even the success of electrostatic demonstrations) can
vary from day to day.
Distribution of Charge via Electron Movement
• Predicting the direction that electrons would move within a
conducting material is a simple application of the two
fundamental rules of charge interaction. Opposites attract
and likes repel.
• The excess negative charge distributes itself throughout the
surface of the conductor. This is because electrons wish to
manipulate their surroundings in an effort to reduce repulsive
affects.
Check your understanding
• Suppose that a conducting sphere is charged positively by some
method. The charge is initially deposited on the left side of the
sphere. Yet because the object is conductive, the charge spreads
uniformly throughout the surface of the sphere. The uniform
distribution of charge is explained by the fact that ____.
a. the charged atoms at the location of charge move throughout the
surface of the sphere
b. the excess protons move from the location of charge to the rest
of the sphere
c. excess electrons from the rest of the sphere are attracted towards
the excess protons
Charging by friction
• When two objects are rubbed together electrons may
be transferred from one object to another. One object
gains electrons and the other object loses electrons,
so both objects have a charge.
• Charging by friction results opposite charges on the
two objects rubbed together.
Charging by Friction
• Rub two insulators together
• ELECTRONS move from one to the other
• One object becomes + the other -
RULE #1 – ONLY ELECTRONS MOVE
When wool is rubbed against a PVC pipe,
the PVC steals electrons from the wool
because it has higher electron affinity
compared to wool. The PVC strip ends
up with a negative charge while the wool
ends up with a positive charge
When wool is rubbed against a Nylon
strip, the wool will steal electrons from
the Nylon because wool has higher
electron affinity than Nylon. As a
result, the Nylon ends up positively
charged and the wool ends up
negative.
How do we know which object will gain
electrons and which will lose electrons?
• electron affinity determines which object will gain
electrons.
• The property of electron affinity refers to the relative
amount of love that a material has for electrons.
High affinity means the material has more pull to
electrons.
• The more love of electrons a material has the more
likely it is to steal electrons from the other object
during charging by friction
2/7 do now
• When a neutral metal sphere is charged by
contact with a positively charged glass rod,
the sphere
1. loses electrons
2. loses protons
3. gains electrons
4. gains protons
• Explain you answer
Objectives
1. Understand the basic properties of electric
charge.
2. Differentiate between conductors and
insulators.
3. Distinguish between charging by contact and
charging by polarization.
Homework:
1. Castle learning
2. Text book - Page 633 #1-6
Triboelectric series
• A triboelectric series is an ordering
of substances with high affinities
on top.
• When any two materials in the
table are rubbed together, the one
which is higher can be expected to
pull electrons from the material
which is lower.
Metal can also be charged by
friction
Law of Conservation of Charge
• The total amount of charge in a closed system
remains constant – charge is not created or
destroyed, it only moves from one object to
another
• The frictional charging process (as well as any
charging process) involves a transfer of electrons
between two objects.
• During all charging processes, the net charge of the
system is conserved.
Charging by Conduction
• Charging by conduction involves the contact of a charged
object to a neutral object.
A metal sphere with
an excess of –
charge is brought
near to a neutral
electroscope.
Upon contact, emove from the
sphere to the
electroscope and
spread about
uniformly.
The metal sphere now
has less excess – charge
and the electroscope
now has a - charge
• When charging by conduction both object have the
same type of charge when separated.
– If A negatively charged object touches a neutral
object the neutral object gains electrons and
becomes negatively charged as well.
– If a positively charged object touches a neutral
object then the neutral object loses electrons and
when separated it is positively charged as well.
• To charge by conduction successfully your charged
and neutral object must be conductors!
Law of Conservation of Charge
• In a closed system, charge is always conserved. The
total amount of charge among the objects is the
same before the charging process starts as it is after
the process ends.
example
•
1.
2.
3.
4.
Two metal spheres having charges of +4.0 ×
10-6 coulomb and +2.0 × 10-5 coulomb,
respectively, are brought into contact and
then separated. After separation, the charge
on each sphere is
8.0 × 10-11 C
8.0 × 10-6 C
2.1 × 10-6 C
1.2 × 10-5 C
Castle learning questions
• A joule is equivalent to a
1. N•m
2. N•s
3. N/m
4. N/s
5. Kg∙m2/s2
• There could be more than one answer.
Polarization - Why a charged object attract
neutral object
• In an atom, the protons are tightly bound in a nucleus and
incapable of movement. In conducting objects, electrons are
so loosely bound that they may be induced into moving from
one portion of the object to another portion of the object.
• By placing a charged object near a neutral conducting object
you can create electron movement.
• No electrons have been added to or subtracted from
the can yet there is a charge at either end of the can;
overall the can is electrically neutral. This arrangement
of charge is called polarization.
• Polarization is the process of separating opposite
charges within an object.
• The polarization process always involves the use of a
charged object to induce electron movement or
electron rearrangement.
• By inducing the movement of electrons within an
object, one side of the object is left with an excess of
positive charge and the other side of the object is left
with an excess of negative charge. Charge becomes
separated into opposites.
• Polarization is not charging – the total charge in a
polarized object is still zero just like before.
A surface charge can be induced on insulators by
polarization
• In an insulator, electrons merely redistribute themselves
within the atom or molecules nearest the outer surface of the
object.
Polarization is Not Charging
• When an object becomes polarized, there is
simply a redistribution of the centers of
positive and negative charges within the
object.
• While there is a separation of charge, there is
NOT an imbalance of charge. When neutral
objects become polarized, they are still
neutral objects.
example
• An inflated balloon which has been rubbed against a person's
hair is touched to a neutral wall and remains attracted to
it. Which diagram best represents the charge distribution on
the balloon and the wall?
a
b
c
d
example
• The diagram below shows three neutral metal
spheres, x, y, and z, in contact and on
insulating stands. Which diagram best
represents the charge distribution on the
spheres when a positively charged rod is
brought near sphere x, but does not touch it?
C
A
B
D
The Electroscope
• An electroscope is a device which is capable of detecting the
presence of a charged object through polarization.
Polarization of an electroscope
Grounding
- + - +- -+ - +
• Since the Earth is very large it
can neutralize:
• negative objects by
RULE #2 electrons
– GROUNDING MAKES AN
ABSORBING
OBJECT
NEUTRAL
• positive objects
by
RELEASING electrons
-
-
Grounding Symbol:
Charging by Induction
• charging by induction method is to charge an object
without actually touching the charged object.
• Charging by induction requires conductor,
polarization, and grounding.
Charging by induction using two conductors
Charging a single sphere by induction
The Importance of a Ground in Induction
Charging
• In the charging by induction cases, charge is never transferred
from the charged object to the neutral object… They do not
touch! The charged object causes the neutral object to
become polarized.
• The neutral object got charged through a
ground.
• A ground can serve as a supplier or receiver of electrons.
Examples of ground
ground
ground
Grounding is also a way of uncharging
an object.
The Need for a Conducting Pathway
• Any object can be grounded provided that the charged atoms
of that object have a conducting pathway between the atoms
and the ground.
Electrons will travel along that pathway.
Charging an electroscope by induction
1. Bring a charged object near the
electroscope
2. The electroscope is being
polarized.
3. Touch the part of the electroscope
that is away from the charged
object.
4. Remove your hand.
5. Remove the charged object.
fundamental principles regarding induction
charging
1. The charged object is never touched to the object
being charged by induction.
2. The charged object does not transfer electrons to or
receive electrons from the object being charged. The
charged object serves to polarize the object being
charged.
3. The object being charged is touched by a ground;
electrons are transferred between the ground and
the object being charged (either into the object or
out of it).
4. The object being charged ultimately receives a charge
that is opposite that of the charged object which is
used to polarize it.
example
•
1.
2.
3.
4.
A charged body may cause the temporary
redistribution of charge on another body
without coming in contact with it. This
process is called
conduction
potential
Charging by friction
induction
Extra practice
Example
1.
An object can not have a charge of
a.
b.
c.
d.
2.
3.2 × 10-19 C
4.5 × 10-19 C
8.0 × 10-19 C
9.6 × 10-19 C
What is the smallest electric charge that can be put on an
object?
a.
b.
c.
d.
9.11 × 10-31 C
1.60 × 10-19 C
9.00 × 109 C
6.25 × 1018 C
Example – change electrons to Coulomb
• What is the net charge of an object possessing
an excess of 6.0 x 106 electrons?
Since there are 1.6 · 10-19 Coulomb in 1 electron, you can
multiply the number of electrons by 1.6 · 10-19 Coulomb to
find the result.
(6.0 · 106 e)(1.60 · 10-19 C/e) = 9.6 x 10-13 C
Example – change Coulomb to electrons
• A metal sphere has a net negative charge of 1.1 x 10-7
coulomb. How many more electrons than protons
are on the sphere?
Since there are 6.25 · 1018 electrons in 1 Coulomb, you can
multiply the number of Coulomb by 6.25 x 1018 electrons to
the result. x = 6.875 x 1011 e
(1.1 · 10-7 C)(6.25 · 1018 e/C) = 6.875 x 1011 e
example
•
If an object possessing an excess of 6.0 × 106 electrons, what
is its charge in Coulombs?
•
Which quantity of excess electric charge could be found on
an object?
0.25 elementary charges
5.25 × 10-19 C
6.40 × 10-19 C
1.60 elementary charges
1.
2.
3.
4.
7.1 Characteristics of uniform circular motion
1. What is uniform circular motion?
2. Describe the magnitude and the direction of velocity of a uniform
circular motion.
3. Describe the magnitude and the direction of acceleration of a
uniform circular motion.
4. Describe the magnitude and the direction of net force of a
uniform circular motion.
5. What does centripetal mean?
6. Why is force required when an object moves in a circle?
7. How is centripetal force related to mass, velocity and radius of the
object moving in a uniform circular path? Give examples to show
your understanding.
7.3 The law of universal gravitation
1. What is inverse squared relationship? Give examples to
show your understanding.
2. What does “universal” in the law of universal gravitation
mean?
3. What is gravity?
4. Write the equation of universal gravitation and indicate
each symbol in the equation mean. Draw a picture to
show your understanding.
5. How is gravitational force related to masses of each object
and how is it related to the distance from the center of
each mass? Give examples to show your understanding.
6. How is value g related to the distance from the center of
Earth?
7. Draw a picture to illustrate that gravity is a field force.
Lab 14
• Static electricity station lab
1/30 do now
• 1) A metallic sphere gains 500 electrons.
a. Determine the amount of ‘elementary charge’ that is
now on the sphere. Be sure to indicate positive or
negative!
b. Calculate the charge on the sphere in coulombs.
End of 5.1.1 - PRACTICE
objectives
• Know:
– Definition of insulator, conductor
– Charge is transferred in solids by electron movement only.
• Understand:
- How charge is transferred by contact and induction
- How surface charge can be induced on insulators by
polarization.
• Be able to:
- Explain how charged object attract neutral objects