Transcript Electricity

Electricity
Structure of matter
 An atom is composed of a variety of subatomic particles.
 The three main subatomic particles are the proton, electron and
neutron.
 The proton and neutron are the most massive of the three subatomic
particles; they are located in the nucleus of the atom
 The proton is charged positively. The neutron does not possess a
charge and is said to be neutral.
 Outside the nucleus are concentric spherical regions of space known
as electron shells. The shells are the home of the negatively
charged electrons.
 Electrons in higher energy shells can move down to lower
energy shells; this movement is accompanied by the release of
energy. Similarly, electrons in lower energy shells can be
induced to move to the higher energy outer shells by the
addition of energy to the atom. If provided sufficient energy, an
electron can be removed from an atom and be freed from its
attraction to the nucleus.
Atomic Structure and Charge
 An atom with equal number of protons and
electrons is electrically neutral
 An atom with more electrons than protons is
negatively charged
 An atom with more protons than electrons is
positively charged
 A charged atom is called an ion.
Question
 Identify the following particles as being charged or
uncharged. If charged, indicate whether they are
charged positively or negatively. (n = neutron, p =
proton, e = electron)
Answer

Answers:
a. Charged Negatively

There are 11 electrons and 10 protons. This results in an imbalance of charge. With
more electrons than protons, the particle is negatively charged.


b. Uncharged

There are 11 electrons and 11 protons. This results in a balance of charge. This particle
is neutral or uncharged.


c. Charged Positively

There are 18 electrons and 20 protons. This results in an imbalance of charge. With
more protons than electrons, the particele is positively charged.
Acquisition of charge
 Electrons are negatively charged and weakly bound to the
atom. Electrons are often removed from and added to
an atom by normal everyday occurrences.
 In order to transfer electrons to or from an object
work must be done.
 Work is the product of force x displacement.
 Often the force is from friction of two objects rubbing
together.
 The protons and neutrons of the nucleus are not
removable by usual everyday methods.
 It would require some form of high-energy nuclear
occurrence to disturb the nucleus and subsequently
dislodge its positively charged protons.
UNIT
 The charge possessed by an object is often
expressed using the scientific unit known as the
Coulomb
 microCoulombs (µC) or nanoCoulombs (nC) are more
commonly used
 an object would need an excess of 6.25 x 1018
electrons to have a total charge of -1 C and of course
an object with a shortage of 6.25 x 1018 electrons would
have a total charge of +1 C
 The charge on a single electron is -1.6 x 10 -19 Coulomb.
 The charge on a single proton is +1.6 x 10 -19 Coulomb.
 The formula for determining the charge on an object in
coulombs:
q=n*e
q= charge of the object
n= number of elementary charges
e= the charge of 1 elementary charge (1.6 x 10 -19 )
Question
 After some rather exhausting counting (and a rather tall
tale), a physics teacher determines that a very small sample
of an object contains ...
 a. ... 8.25749 x 1017 protons and 5.26 x 1014 electrons; the
charge on this object is ____ Coulombs.
 b. ... 3.12 x 1014 protons and 4.5488 x 1016 electrons; the
charge on this object is ____ Coulombs.
 c. ... 2.40277 x 1019 protons and 9.88 x 1016 electrons; the
charge on this object is ____ Coulombs.
 d. ... 2.6325 x 1015 protons and 2.6325 x 1015 electrons; the
charge on this object is ____ Coulombs.
Answer
 Method: Subtract then multiply the difference by the
charge of a proton or electron - 1.6 x 10-19 C.
 Answers:
 a. 0.132 C
 b. 0.00723 C (7.23 x 10-3 C)
 c. 3.83 C
 d. 0 Coulombs
Question
 A sphere has a negative charge of 6.4 x 10-7 coulomb.
Approximately how many electrons must be removed to
make the sphere electrically neutral?
Answer
 q = n*e
 6.4 x 10-7C = n(1.6 x 10-19C)
 n= 4.0 x 1012
 Not only do electrostatic occurrences permeate the
events of everyday life (static cling and getting
shocked), without the forces associated with static
electricity, life as we know it would be impossible.
Electrostatic forces - both attractive and repulsive in
nature - hold the world of atoms and molecules
together in perfect balance. Without this electric force,
material things would not exist. Atoms as the building
blocks of matter depend upon these forces. And
material objects, including us Earthlings, are made of
atoms and the acts of standing and walking, touching
and feeling, smelling and tasting, and even thinking is
the result of electrical phenomenon. Electrostatic forces
are foundational to our existence.
electric force
 The electric force is a non-contact force
 Any charged object can exert this force upon other
objects - both charged and uncharged objects.
 Ex: balloon lifts hair or paper after being rubbed
 Opposites attract. And likes repel.
 a positively charged object will attract a negatively
charged object.
 a positively charged object will exert a repulsive force
upon a second positively charged object. This repulsive
force will push the two objects apart.
 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; and negatively
charged objects and neutral objects attract each
other.
 This electric force exerted between two oppositely
charged objects or two like charged objects is a force
in the same sense that friction, tension, gravity and air
resistance are forces.
 Must follow laws and principles that describe any
force such as Newtons third law.
 According to Newton's third law, a force is simply a
mutual interaction between two objects that results in
an equal and opposite push or pull upon those objects.
 Object A exerts a rightward push upon Object
B. Object B exerts a leftward push upon Object
A. These two pushing forces have equal
magnitudes and are exerted in opposite
directions of each other. Because of the away
from nature of the mutual interaction, the force
is said to be repulsive.
 Object C exerts a leftward pull upon object D.
Object D exerts a rightward pull upon Object C.
Again, each object does its own pulling of the
other. Just as before, these two forces have equal
magnitudes and are exerted in opposite directions
of each other. However in this instance, the
direction of the force on Object D is towards Object
C and the direction of the force on Object C is
towards object D. Because of the towards each
other nature of the mutual interaction, the force is
described as being attractive.
 https://www.youtube.com/watch?v=-w-GoSJpvdw
 https://www.youtube.com/watch?v=SnabbDPmlUs
Electroscope
Conductors and Insulators
 Conductors are materials that permit electrons to
flow freely from particle to particle. A conducting
material will permit charge to be transferred across the
entire surface of the object.
 Insulators are materials that impede the free flow of
electrons from atom to atom and molecule to
molecule. If charge is transferred to an insulator at a
given location, the excess charge will remain at the
initial location of charging
 The human body is a conductor. When the body acquires
a static charge it has a tendency to distribute that charge
throughout the surface of the body. The effects of excess
charge on the body are often demonstrated using a Van
de Graaff generator. When a student places their hand
upon the static ball, excess charge from the ball is
shared with the human body. Being a conductor, the
excess charge could flow to the human body and spread
throughout the surface of the body, even onto strands of
hair. As the individual strands of hair become charged,
they begin to repel each other. Looking to distance
themselves from their like-charged neighbors, the
strands of hair begin to rise upward and outward
 https://www.youtube.com/watch?v=7qgM1A3pgkQ
 https://www.youtube.com/watch?v=ubZuSZYVBng
Question
 One of these isolated charged spheres is copper and
the other is rubber. The diagram below depicts the
distribution of excess negative charge over the surface
of two spheres. Label which is which and support your
answer with an explanation.
Answer
 A is rubber and B is copper.
 Sphere A shown a non-uniform distribution of excess
charge; so sphere A must be made of an insulating
material such as rubber. Sphere B shows a uniform
distribution of excess charge; one would reason that it
is made of a conductor such as copper.
 https://www.youtube.com/watch?v=qUhxmXZwPmg
 (induction, conductors, insolators)
 As fuel is pumped from the tanker car to a reservoir,
charge can quickly build up as the fluid flows through the
hoses. This static charge can create sparks capable of
igniting the fuel. By connecting the body of the tanker car
to the ground, the static charge can be transferred to the
ground. A metal wire is used since metals are conductive
and allow charge to flow through them
Polarization
 Relative to the protons of the nucleus, electrons are
loosely bound.
 In conducting objects, they are so loosely bound that they
may be induced into moving from one portion of the object
to another portion of the object.
 To get an electron in a conducting object to get up and go,
all that must be done is to place a charged object nearby
the conducting object.
 Polarization is the process of separating opposite
charges within an object. 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.
 A rubber balloon is charged negatively by rubbing it
against animal fur. The negatively charged balloon is
brought near the aluminum can, the electrons within the
can will experience a repulsive force. Many of these
electrons will be induced into moving away from the
repulsive balloon into the opposite side of the can. This
electron movement leaves atoms on the balloon's side of
the can with a shortage of electrons; they become
positively charged. And the atoms on the side opposite of
the can have an excess of electrons; they become
negatively charged. The two sides of the aluminum pop
can have opposite charges. Overall the can is electrically
neutral; it's just that the positive and negative charge has
been separated from each other. We say that the charge
in the can has been polarized.
Polarization in insulators
 Polarization can occur within insulators, but the
process occurs in a different manner than it does
within a conductor.
 In a conducting object, electrons are induced into
movement across the surface of the conductor from
one side of the object to the opposite side.
 In an insulator, electrons merely redistribute
themselves within the atom or molecules nearest
the outer surface of the object.
 the biggest misconception that pertains to polarization
is the belief that polarization involves the charging of
an object.
 Polarization is not charging!
 When an object becomes polarized, there is simply
a redistribution of the negative charges within the
object. The overall charge is still neutral!
Question
 Which of the diagrams below best represents the
charge distribution on a metal sphere when a positively
charged plastic tube is placed nearby?
Answer
 Answer: D
 In each case, the tube (in pink) is charged. Its charge
should polarize the metal sphere. This is not shown in
A; so A can be ruled out. In B, C and D the sphere is
polarized. But in B and C, the diagram shows the
separation of charge in a manner that would indicate
an attraction between like charges. On the other hand,
D shows that the negative charge on the sphere is
attracted to the positive tube.
Charging
 any charging process involves a transfer of electrons between two
objects.
 Charge is not created from nothing. The appearance of
negative charge is the result of its acquisition of electrons
and these electrons must come from somewhere
 Prior to the charging, both objects are electrically neutral. The
net charge of the system is 0 units.
 After the charging process, the more electron-loving object
may acquire a charge of -12 units; the other object acquires a
charge of +12 units. Overall, the system of two objects has a
net charge of 0 units.
 Charge is always conserved - law of conservation of charge.
How to charge an object
 The frictional charging process results in a
transfer of electrons between the two objects that
are rubbed together.
How to charge an object
 Induction:
 The charged object is never touched to the object being
charged by induction.
 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.
 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).
 The object being charged ultimately receives a charge that is
opposite that of the charged object that is used to polarize it.
Induction
Induction
How to charge an object
 Charging by conduction involves the contact of
a charged object to a neutral object.
 only a conductor can conduct charge to another
conductor (for this class)
Remove Charge
 Grounding is the process of removing the excess
charge on an object by means of the transfer of
electrons between it and another object of
substantial size
 Grounding requires a conducting pathway between
the ground and the object to be grounded.
Electrons will travel along that pathway.
Coulomb's Law
 The electrical force, like all forces, is typically
expressed using the unit Newton.
 Being a force, the strength of the electrical interaction is
a vector quantity that has both magnitude and
direction.
 The direction of the electrical force is dependent upon
whether the charged objects are charged with like
charge or opposite charge and upon their spatial
orientation: (opposites attract and likes repel)
Coulomb’s law
 k= Electrostatic constant = 8.99 x 109 Nm2/C2
 Coulomb's law states that the electrical force
between two charged objects is directly
proportional to the product of the quantity of
charge on the objects and inversely proportional to
the square of the separation distance between the
two objects.
 Double Distance:
 F 4x smaller (1/4 as strong) F/4
 One charge is doubled:
 F would double 2F
 Both charges are doubled and distance is cut in half:
 16F
 Both charges are doubled and distance is doubled:
 No Change
Question
 Two balloons are charged with an identical quantity and
type of charge: -6.25 nC. They are held apart at a
separation distance of 61.7 cm. Determine the
magnitude of the electrical force of repulsion between
them.
Answer
 Given:
 Q1 = -6.25 nC = -6.25 x 10-9 C
 Q2 = -6.25 nC = -6.25 x 10-9 C
 d = 61.7 cm = 0.617 m
 Felect = k • Q1 • Q2 / d2
 Felect = (9.0 x 109 N•m2/C2) • (6.25 x 10-9 C) • (6.25 x
10-9 C) / (0.617 m)2
 Felect = 9.23 x 10-7 N (positive means repulsive)
Question
 Two balloons with charges of +3.37 µC and -8.21 µC
attract each other with a force of 0.0626 Newton.
Determine the separation distance between the two
balloons.
Answer

Given:

Q1 = +3.37 µC = +3.37 x 10-6 C

Q2 = -8.21 µC = -8.21 x 10-6 C

Felect = -0.0626 N (use a - force value since it is attractive)

As mentioned above, the use of the "+" and "-" signs is optional. However, if they are used, then they have to be used consistently for the Q values and the F values. Their use in the equation is illustrated in this problem.

The final step of the strategy involves substituting known values into the Coulomb's law equation and using proper algebraic steps to solve for the unknown information. In this case, the algebra is done first and the
substitution is performed last. This algebra and substitution is shown below.

Felect = k • Q1 • Q2 / d2 d2 • Felect = k • Q1 • Q2

d2 = k • Q1 • Q2 / Felect

d = SQRT(k • Q1 • Q2) / Felect

d = SQRT [(9.0 x 109 N•m2/C2) • (-8.21 x 10-6 C) • (+3.37 x 10-6 C) / (-0.0626 N)]

d = Sqrt [ +3.98 m2 ]

d = +1.99 m
 Does Coulomb’s Law equation look familiar?
Comparing Electrical and
Gravitational Forces
 The two equations have a very similar form.
 Both equations show an inverse square relationship between force and
separation distance.
 Both equations show that the force is proportional to the product of the
quantity that causes the force - charge in the case of electrical force and
mass in the case of gravitational force.
 differences between these two forces.

k versus G - reveals that the Coulomb's law constant (k) is significantly
greater than Newton's universal gravitation constant (G). Subsequently
a unit of charge will attract a unit of charge with significantly more force
than a unit of mass will attract a unit of mass.
 gravitational forces are only attractive; electrical forces can be either
attractive or repulsive.
Electric Fields
 An electric field is a region around a charged
particle through which a force is exerted on
another charged particle
 An electric field line is the imaginary line along
which a positive test charge would move in an
electric field
 Field around a positive and negative point charge
Field between opposite
charges
Field around two positive
charges
Field lines between two
negative charges
 Field lines never touch or intersect
 The electric field strength around the charged sphere
varies inversely with the square of the distance from
the sphere (point charge)
Field between oppositely
charged parallel plates
 The magnitude of the electric force on an electron
or proton located at any point between two
oppositely charged parallel plates is the same
 The electric force acting on either of these charged
particles causes it to accelerate toward the plate of
opposite sign (opposites attract)
Electric Field Strength
 Electric Field strength is :the force on a stationary
positive test charge per unit charge in an electric
field
 E=Fe/q
 Electric field strength is a vector
 Units are newtons per coulombs
Question
 What is the magnitude of the electric field strength at a
point in a field where an electron experiences a 1 N
force?
 E=Fe/q
 1.0N/ 1.6 x 10-19C
 6.3 x 1018N/C
Electric Field and the
Movement of Charge
 objects naturally move from high potential energy to low
potential energy under the influence of the field force (ex
objects fall, positive charge moves toward a negative
charge)
 work must be done by an external force to move an
object against nature - from low potential energy to
high potential energy
 The exertion of work by an external force would in
turn add potential energy to the object.
Electric Field and the Movement
of Charge
Electric Potential
 The amount of force involved in doing the work is
dependent upon the amount of charge being moved
 The greater the charge on the test charge, the
greater the force ( according to Coulomb’s Law) and
the more work that would have to be done on it to
move it the same distance
 This work would change the potential energy by an
amount that is equal to the amount of work done
 electric potential energy is dependent upon:
 1) Electric charge - a property of the object
experiencing the electrical field, and
2) Distance from source - the location within the electric
field
Electric Potential Difference
 V= W/q V=potential difference, W=work (PE),
q=charge
 The standard metric unit on electric potential difference
is the volt, abbreviated V
 One Volt is equivalent to one Joule per Coulomb
 If the electric potential difference between two locations is 1
volt, then one Coulomb of charge will gain 1 joule of
potential energy when moved between those two locations.
 If the electric potential difference between two locations is 3
volts, then one coulomb of charge will gain 3 joules of
potential energy when moved between those two locations.
Electric Potential Difference
 Electric Potential energy = work of the field on a
charge
 Work brings the charge in motion – creates an
electrical current
 The change in electric potential energy is measured in
Volts
Electrons moving through potential differences the energy
may not be in joules:
Instead we can use: Electron Volts (energy needed to
move one electron through one volt of potential
difference)
W=V/q
1eV = 1.6x10-19J
Potential Difference or
Voltage
Potential Difference
Question
 A +3μC charge is moved through a potential difference
of 640V. What is the potential energy in Joules and
electron volts?
Answer
 V=W/q = W=qV
 (3x10-6C)*(640V) = 1920x10-6 Joules
 In eV:
1eV = 1.6x10-19J
X
x= 1.2 x1016eV
1920 x 10-6J
Question
 A proton moves from rest and gains 8.35 x 10-14J of
KE. What is the final velocity of the proton?
 KE=1/2mv2
 8.35 x 10-14J =(1/2)(1.67x10-27kg)V2
 https://www.youtube.com/watch?v=NNR-sd58p-U
 Physics demos – electricity
 https://www.youtube.com/watch?v=MiL0wCZr0Mw
 MRI
 https://www.youtube.com/watch?v=mGkU8cHHSMU
 Understanding electricity
 https://www.youtube.com/watch?v=CX84l5ZZHVg
 How Batteries work
Electric Current
 In order to make electric current flow the following
conditions must be satisfied:
 1- The materials must be conductors (allow the flow of
electrons)
 2- The conductor must be connected to a source or
device that creates an electric field: a potential
difference exists between the ends of the conductor
(ex. Battery or generator)
 3- The source and the conductor must form a closed
loop called a circuit.
The Ampere
 The amount of charge flowing past a given point in a
conductor is expressed in coulombs per second
 If one coulomb passes a point in a conductor each
second the current in the conductor is one ampere
 Ampere is the SI unit for Current (I)
 I= ∆q/t q= charge in coulombs t= time in seconds I=
current in Amperes
7A
5A
3A
A
What is the current at A?
Battery Powered circuit
• work must be done on a positive test charge to move it through the
cells from the negative terminal to the positive terminal. This work
would increase the potential energy of the charge and thus increase
its electric potential. As the positive test charge moves through the
external circuit from the positive terminal to the negative terminal,
it decreases its electric potential energy and thus is at low potential
by the time it returns to the negative terminal. If a 12 volt battery is
used in the circuit, then every coulomb of charge is gaining 12
joules of potential energy as it moves through the battery. And
similarly, every coulomb of charge loses 12 joules of electric
potential energy as it passes through the external circuit. The loss
of this electric potential energy in the external circuit results in a
gain in light energy, thermal energy and other forms of nonelectrical energy (voltage drop)
What is the voltage at points A and D?
• The internal circuit is the part of the circuit where energy is
being supplied to the charge. For the simple batterypowered circuit that we referred to, the portion of the
circuit containing the electrochemical cells is the internal
circuit (battery). The external circuit is the part of the
circuit where charge is moving outside the cells through the
wires on its path from the high potential terminal to the
low potential terminal. The movement of charge through
the internal circuit requires energy since it is an uphill
movement in a direction that is against the electric field.
The movement of charge through the external circuit is
natural since it is a movement in the direction of the
electric field.
How a Battery Works
• The electrochemical cells in a battery supply
the energy to do work upon the charge to
move it from the negative terminal to the
positive terminal. By providing energy to the
charge, the cell is capable of maintaining an
electric potential difference across the two
ends of the external circuit. Once the charge
has reached the high potential terminal, it will
naturally flow through the wires to the low
potential terminal.
FUN FACTS
• 1) An electrochemical cell supplies the energy needed to move a charge
from a low potential location to a high potential location.
• 2)The charge that flows through a circuit originates in the wires of the
circuit. The charge carriers in wires are simply the electrons possessed by
the atoms that make up the wires.
• 3) Charge moves abnormally slowly - on average, about 1 meter in an hour
- through a circuit. Yet as soon as a switched is turned to ON, charge
located everywhere within the circuit begins to move. (lights up
immediately)
• 4) The rate at which charge flows is everywhere the same within an
electric circuit (current). The rate at which charge flows into a light bulb is
the same as the rate at which charge flows out of a light bulb.
• 5) An electrical appliance such as a light bulb transforms the electrical
energy of moving charge into other forms of energy such as light energy
and thermal energy. Thus, the amount of electrical energy possessed by a
charge as it exits an appliance is less than it possessed when it entered the
appliance.
Power
• Power is the rate at which electrical energy is
supplied to a circuit or consumed by a load
(light bulb, motor etc..) unit is Watt
• Or the rate at which work is done
• Whether energy gained by the charge at the
energy source or the energy lost by the charge
at the load, electrical power refers to the rate
at which the charge changes its energy
• a light bulb is rated at 60 watts, then there are
60 joules of energy delivered to the light bulb
every second. A 120-watt light bulbs draws
120 joules of energy every second.
• Power is the rate at which energy is added to
or removed from a circuit by a battery or a
load. (equation 1)
• Current is the rate at which charge moves
past a point on a circuit. (equation 2)
• Electric potential difference across the two
ends of a circuit is the potential energy
difference per charge between those two
points (equation 3)
• The three equations can be related in the
following way:
Question
• Your 60-watt light bulb is plugged into a 110-volt
household outlet and left on for 3 hours. The
utility company charges you $0.11 per
kiloWatt•hr. How much will this cost you?
• The energy consumed can be determined from
knowledge of the power (60 Watts) and the time
(3 hrs). The energy consumed is 180 Watt•hr or
0.180 kW•hr. Each kW•hr costs 11 ¢ pr $0.11.
Now simply multiply the cost per ¢ by the
amount of ¢ of energy consumed. The result is
just a little short of 2 cents.
Resistance
• Resistance is the hindrance to the flow of
charge.
• While the electric potential difference
established between the two terminals
encourages the movement of charge, it is
resistance that discourages it. The rate at
which charge flows from terminal to terminal
is the result of the combined effect of these
two quantities.
Ohm’s Law
Ohm’s Law
• Electric current is directly proportional to the
voltage
• Resistance in a circuit causes the potential to
drop
• R=V/I
• A drop in potential occurs as electrical energy
is transformed to other forms (heat, light,
motion)
V
I
R
Question
• How much current flows through a 100 watt
bulb connected to a 120v power supply?
• What is the resistance?
• Draw the circuit diagram.
Answer
• P=VI I=.83A
• R=V/I R=144.6Ʊ
Resistance
Resistance
• The standard metric unit for resistance is the
ohm (Greek letter omega ) Ω
• L represents the length of the wire (in
meters), A represents the cross-sectional area
of the wire (in meters2), and ρ represents the
resistivity of the material (in ohm•meter).
Question
• A potential difference of 60 volts is applied
across a 15-ohm resistor. What is the power
dissipated in the resistor?
• P=V2/R = 240W
Question
• A current of 0.40 ampere is measured in a 150
ohm resistor. How much energy is expended
by the resistor in 30seconds?
• W=I2Rt =720J
Resistance
• 1) The longer the wire, the more resistance that there
will be. (direct relationship)
• 2) Wider wires have a greater cross-sectional area and
the less resistance that there will be to the flow of
electric charge. (indirect relationship)
• 3) Some materials are better conductors than others
and offer less resistance to the flow of charge. Silver is
one of the best but is never used in household wires
due to its cost. Copper and aluminum are among the
least expensive materials.
• 4) Temperature- As temperature increases, resistance
increases
(https://www.youtube.com/watch?v=XxBn_Wzm0aI)
Resistance
• Resistance is directly related to the length of
the wire
– The longer the wire, the greater the resistance
• Resistance is indirectly related to the diameter
of the wire
– The greater the diameter of a wire, the less its
resistance
• The conducting ability of a material is often indicated by
its resistivity. The resistivity of a material is dependent
upon the material's electronic structure and its
temperature. For most (but not all) materials, resistivity
increases with increasing temperature
• Material Resistivity (ohm•meter) (see ref. Table)
• Silver 1.59 x 10-8
• Copper 1.7 x 10-8
• Gold 2.2 x 10-8
• Aluminum 2.8 x 10-8
• Tungsten 5.6 x 10-8
• Iron 10 x 10-8
• Platinum 11 x 10-8
• Lead 22 x 10-8
• Glass 1010 - 1014
• Hard Rubber 101
Question
• Determine the resistance of a 1-mile length of
copper wire with a diameter of 0.2117 cm.
(Given: 1 mile = 1609 meters)
• L=1609 m
• ρ=1.72 x 10-8 Ωm
• A=πr2=(3.14)(.10585)2
• R = (1.7 x 10-8 ohm •m) • (1609 m) / (3.519 x
10-6 m2)
• R = 7.8 (7.7709 ohm)
Ruby
 I LOVE RUBY
 RUBYS AMAZING
 VEGA IS GROSS
 EW VEGA
 I HATE VEGA
 EVERYONE HATES VEGA
• http://www.youtube.com/watch?v=Z77IzaXGcg
• http://www.youtube.com/watch?v=PUHzRW_
6sYE
– 9:10 mark
Can you draw the circuit?
Which circuit diagram?
Series Circuit
-
-
-
-
- If there is only one path for the current we say the bulbs are
- connected in SERIES.
- - - -
Series Circuit
There is only one path for current to travel so
the current is the same everywhere on the
path
• When two resistors are connected in series
the combined resistance is equal to the sum of
the individual resistors resistances

– Rcombined = R1+R2+R3+…
Question
• A 50 ohm resistor, an unknown resistor R, a
120V source, and an ammeter are connected
in a series circuit. The ammeter reads .5 A.
• 1- Draw the Circuit
• 2-Calculate the equivalent resistance
• 3- Determine the resistance of Resister R
• 4-Calculate the power dissipated by the 50
ohm resistor
•
•
•
•
1- draw
2-240 ohms
3-190 ohms
4-12.5W
Parallel Circuit
-
-
-
-
-
the current has two
- Here
paths.
-Any circuit with more than one
- path means that the bulbs are
-
connected in PARALLEL.
Parallel Circuit

Each branches current comes from the
source, therefore the current through the
source is greater than the current through any
one of the branches current
Parallel Circuits Cont…
There are two or more paths for current to
follow so the combined resistance is less than
any of the individual resistors by themselves
 Parallel connection of bulbs in a circuit allows
the remaining bulbs to receive current after
one bulb is removed or goes out and no longer
has current traveling through that branch

Open Switch
Closed Switch
Conditions necessary for an electric
current to flow:
• A complete circuit
• Something to push the current around the
circuit
– Battery
– Power supply
– Cell
Electric Current
• Current is a flow of electric charge
• Requires electrical energy provided by a
battery or power supply
• Measured in Amperes or Amps (A)
Direction of Current Flow
Ammeter
• Measures the flow of charge (current) in
amperes
– Connected in series to make measurements
Series Connectivity
Conducting Medium
• Current flows through a material (wire) that is
a good conductor of an electric current
– Good conductors: Most metals, including copper,
silver, gold, and steel
• The metal is usually surrounded by a good
insulator (a material that does not conduct an
electric current well)
– Good insulators: Polymers (plastics), minerals,
glass
Potential Difference or Voltage
• Two points where a difference in energy exists
• Can be measured across a circuit component,
like a light bulb
• Measured in Volts (V)
Electro-Motive Force (e.m.f)
• Represents a potential difference across the
source of electrical energy in a circuit
• Measured in volts
– Name is deceiving because it is not a force but
actually is a potential difference and behaves like a
force that moves charges (creates current)
• Source of electrical energy
– Battery
» Chemical reaction
– Power Source
Voltmeter
• A voltmeter is used to measure potential
difference (p.d.) in a circuit
– Measures the potential difference between two
points in volts
• Connected in parallel to make measurement
Parallel Connectivity
Changing Current
• Current is directly related to potential
difference (volts)
– If current increases, potential difference increases
– If current decreases, potential difference
decreases
• Current is indirectly related to resistance
(ohms)
– If current increases, resistance decreases
– If current decreases, resistance increases
Circuit Simulation
• http://phet.colorado.edu/en/simulation/circui
t-construction-kit-dc
– Run Now