Download Unit 10AB Static Electricity and Circuits

Electricity & Magnetism
Part I
Static Electricity
Unit 10 Concept Map
Electricity and Magnetism
Static Electricity
Current Electricity Magnetism & Electromagnetism
The Electrical Charge Carrier
• The Electron
– Negatively charged
– 9.11x10-31 kg
• The Proton
– Positively charged
– 1.67x10-27 kg
Why is the electron principally responsible
in determining electric charge?
Charge Basics




Opposite charges attract
Like charges repel
Electrons and protons have equal and opposite
charges
Lowest possible charge is that of electron or
proton (no fractional charges…yet)
Benjamin Franklin
1706-1790
• Famous kite experiment
• First to give charges the names positive
and negative
• First to realize Law of
Conservation of Charge
• Invented the lightning rod
The SI Unit of Charge
The Coulomb (C)
6.25x1018 electrons (or protons) are needed to
make one Coulomb
The charge on one single electron/proton
1.6x10-19 C
See reference table for values
Charles-Augustin de Coulomb
1736-1806
Questions?
• How does an object become negatively
charged?
• How does an object become positively
charged?
• What is the net charge in Coulombs of
5 electrons?
• What is the number of protons that make
up a charge of 10 nanoCoulombs?
Law of Conservation of Charge
• Electric charge can neither be created nor
destroyed
-5
-8
-8
-11
Transferring Charge
The Electroscope
• A device used to detect electric charge
Charging by Induction
• Isolating charge
without physical
contact between
objects
• Once charged
rod is removed,
the electroscope
stays neutrally
charged
Charging by Conduction
• Isolating electric
charge by
physical contact
• Once rod is
removed, the
electroscope
remains charged
Permanently Charging by Induction
Coulomb’s Law

There exists an electrostatic force
between charged objects that is directly
proportional to the magnitude of the
charges and indirectly proportional to the
square of the distance between them.
This is another Inverse-Square law
 This force could be attractive or repulsive

Coulomb’s Law
F21 indicates force on q1 due to q2
F12 indicates force on q2 due to q1
Coulomb’s Law
kq1q2
Fe  2
r
Coulomb’s Constant
kq1q2
Fe  2
r
N m
k  9.0 x10
2
C
9
2
Let’s Try a Problem
F21 indicates force on q1 due to q2
The Van de Graaff Generator
• Generates large static
charges that build up on dome
• Some generators can charge
to thousands of volts
• They are generally safe, but
caution should be heeded
Electric Fields
• An electric field is an invisible force field
that affects electric charges
• The field is defined based on how it affects
a positive test-charge
• All charged objects are assumed to have
an electric field associated with them
Electric Field Mapping
Electric Field Around a Positively
Charged Object
Electric Field Around
Charged Pairs
Electric Field of a Set of
Parallel Plates
Electric Field Mapping Rules
• E-Field lines must never touch or cross
themselves or other field lines
• E-Field lines run out of a positive charge
and into a negative charge
• E-Field lines must intersect charged object
at right angle (90o)
• Number and density of lines indicate field
strength or intensity
Electric Field Intensity
Fe
E
q
q represents charge on test-charge
Units of electric field intensity are
Newtons per Coulomb
Electric Field Equation for
Point Charges
kQ
E 2
r
Capital Q indicates charge on the object
Electric Potential Energy
• Electric potential energy is the energy
stored within an electric field
• The work done in moving a charge within
an electric field is equal to the potential
energy stored
• The kinetic energy gained by a charged
particle within an electric field is equal to
the potential energy lost
• What are the units for EPE?
Work-Energy Theorem Review
W  KE
W  EPE
Ei  E f
Electric Potential
• Electric potential is the ratio of the work
done on a charged particle within an
electric field divided by the particle’s
charge
• Units are Joules per Coulomb
• Other terms used for electric potential are
electric potential difference and voltage
Electric Potential
W
V
q
Units of Electric Potential are Joules per Coulomb or Volts
Electric Fields Within
a Charged Object
Potential Inside a Conductor
Electric Field of a Set of
Parallel Plates
The Capacitor
• Capacitor Uses
–
–
–
–
Frequency tuner
Power supplies
Filter
Block DC current
Capacitance of Parallel Plates
C
0 A
d
 0  8.85 x10
12
2
C
2
N m
Capacitance
(in terms of Charge and Voltage)
Q
C
V
Millikan Oil Drop Experiment
E & M Part 2
Current Electricity
•
•
•
•
•
•
Current
Resistance
Voltage
Ohm’s Law
Power
Circuits
– Series
– Parallel
Electric Current
• Time rate of flow of
electric charge
• I represents electric
current
• Units of current are
Coulombs per second
(C )
 ( Ampere)
( s)
q
I
t
Electrical Resistance
• The opposition to steady electric current
flow
• The unit of resistance is the Ohm (W)
• Similar to friction there is no such thing as
zero resistance
Carbon
Resistor
Resistance in Electrical Conductors
i.e. wires
• Resistance depends on:
– Length of wire
– Thickness of wire
– Type of material used (metal)
– Temperature
– How do you think each one of these
parameters effects resistance?
Resistance in Electrical Conductors
L
R
A
R is resistance
L is wire length
A is cross-sectional area
 is resistivity of conductor
Resistance of Electrical Conductors
L
R
A
Area
Wire Gauges
Resistivity Table
The Simple Circuit
• Needed for circuit
– Voltage source
– Complete path
– Load
Electrical Circuit Analogy
Battery
Light Bulb
Schematic Symbols
Electron-Flow Current
V
R
I
P  IV
2
V
P
R
PI R
2
Series Circuit
• Circuit that has only one path for current to flow.
Series Circuit Analogy
Battery
Series Circuit Schematic
Series Circuit Equations
RTotal  R1  R2  ...  Rn
I Total  I1  I 2  ...  I n
VTotal  V1  V2 ...  Vn
P  IV
Parallel Circuit
• Circuit that has more
than one path for
current to flow.
Parallel Circuit Analogy
Battery
Parallel Circuit Schematic
Parallel Circuit Equations
1
RTotal
1
1
1
 
 ... 
R1 R2
Rn
I Total  I1  I 2  ...  I n
VTotal  V1  V2  ...  Vn
P  IV
Kirchoff’s Law of Current
• The current going into a junction (node) is
equal to the current coming out
????????
Which one of these is correct?
Electrical Safety
• Never Intentionally take a shock!
Electrical Safety
• Remove Jewelry, watches, rings, etc.
Electrical Safety
• Use one hand (if possible) on live circuit
Electrical Safety
• Strictly follow lab instructions
Electrical Safety
• Absolutely NO HORSING AROUND!!!
Electrical Safety
• Remember: Current KILLS, not Voltage
– 5 mA = 0.005 A
– 15 mA = 0.015 A
– 20 mA = 0.020 A
– 100 mA = 0.100 A
– 200 mA = 0.200 A
Sensation felt
Painful
Loss of muscle control
Heart fibrillation
Severe burns, Death
Resistor
Color Code