Transcript Honors Physics Unit 10 Notes

Chapter 16
Section 1 Electric Charge
Preview
• Statics
• Circuits
• Electricity and Magnetism
Chapter 16
Section 1 Electric Charge
Objectives
• Understand the basic properties of electric charge.
• Differentiate between conductors and insulators.
• Distinguish between charging by contact, charging
by induction, and charging by polarization.
Chapter 16
Section 1 Electric Charge
Properties of Electric Charge
• There are two kinds of electric charge.
– like charges repel
– unlike charges attract
• Electric charge is conserved.
– Positively charged particles are called protons.
– Uncharged particles are called neutrons.
– Negatively charged particles are called electrons.
Chapter 16
Section 1 Electric Charge
Electric Charge
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Visual Concept
Chapter 16
Section 1 Electric Charge
Properties of Electric Charge, continued
• Electric charge is quantized. That is, when an object
is charged, its charge is always a multiple of a
fundamental unit of charge.
• Charge is measured in coulombs (C).
• The fundamental unit of charge, e, is the magnitude
of the charge of a single electron or proton.
e = 1.602 176 x 10–19 C
Chapter 16
Section 1 Electric Charge
The Milikan Experiment
Chapter 16
Section 1 Electric Charge
Transfer of Electric Charge, continued
• Insulators and conductors can be charged by contact.
• Conductors can be charged by induction.
• Induction is a process of charging a conductor by
bringing it near another charged object and
grounding the conductor.
Chapter 16
Visual Concepts
Charging by Induction
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Visual Concept
Chapter 16
Section 1 Electric Charge
Transfer of Electric Charge, continued
• A surface charge can be
induced on insulators by
polarization.
• With polarization, the
charges within individual
molecules are realigned
such that the molecule
has a slight charge
separation.
Chapter 16
Section 2 Electric Force
Objectives
• Calculate electric force using Coulomb’s law.
• Compare electric force with gravitational force.
• Apply the superposition principle to find the resultant
force on a charge and to find the position at which the
net force on a charge is zero.
Section 2 Electric Force
Chapter 16
Coulomb’s Law
• Two charges near one another exert a force on one
another called the electric force.
• Coulomb’s law states that the electric force is proportional to the magnitude of each charge and inversely
proportional to the square of the distance between
them.
qq 
Felectric  kC  1 2 2 
 r 
electric force = Coulomb constant 
 charge 1 charge 2 
2
distance


Chapter 16
Section 2 Electric Force
Superposition Principle
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Visual Concept
Chapter 16
Section 2 Electric Force
Coulomb’s Law, continued
• The Coulomb force is a field force.
• A field force is a force that is exerted by one object
on another even though there is no physical contact
between the two objects.
Chapter 16
Section 3 The Electric Field
Electric Field Strength
• An electric field is a region where an electric force on
a test charge can be detected.
• The SI units of the electric field, E, are newtons per
coulomb (N/C).
• The direction of the electric field vector, E, is in the
direction of the electric force that would be exerted on
a small positive test charge.
Chapter 16
Section 3 The Electric Field
Electric Fields and Test Charges
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Visual Concept
Chapter 16
Section 3 The Electric Field
Electric Field Strength, continued
• Electric field strength depends on charge and
distance. An electric field exists in the region around
a charged object.
• Electric Field Strength Due to a Point Charge
q
E  kC 2
r
electric field strength = Coulomb constant 
charge producing the field
 distance 
2
Chapter 16
Section 3 The Electric Field
Calculating Net Electric Field
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Visual Concept
Chapter 16
Section 3 The Electric Field
Electric Field Lines
• The number of electric
field lines is proportional
to the electric field
strength.
• Electric field lines are
tangent to the electric
field vector at any point.
Chapter 16
Section 3 The Electric Field
Rules for Drawing Electric Field Lines
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Visual Concept
Chapter 16
Section 3 The Electric Field
Rules for Sketching Fields Created by Several
Charges
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Visual Concept
Chapter 17
Section 1 Electric Potential
Electrical Potential Energy
• Electrical potential energy is potential energy
associated with a charge due to its position in an
electric field.
• Electrical potential energy is a component of
mechanical energy.
ME = KE + PEgrav + PEelastic + PEelectric
Chapter 17
Section 1 Electric Potential
Electrical Potential Energy
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Visual Concept
Chapter 17
Section 1 Electric Potential
Potential Difference
• Electric Potential equals the work that must be
performed against electric forces to move a charge
from a reference point to the point in question,
divided by the charge.
• The electric potential associated with a charge is the
electric energy divided by the charge:
PEelectric
V
q
Chapter 17
Section 1 Electric Potential
Potential Difference, continued
• Potential Difference equals the work that must be
performed against electric forces to move a charge
between the two points in question, divided by the
charge.
• Potential difference is a change in electric potential.
PEelectric
V 
q
change in electric potential energy
potential difference 
electric charge
Chapter 17
Section 1 Electric Potential
Potential Difference
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Visual Concept
Chapter 17
Section 1 Electric Potential
Potential Difference, continued
• The potential difference in a uniform field varies with
the displacement from a reference point.
• Potential Difference in a Uniform Electric Field
∆V = –Ed
potential difference = –(magnitude of the electric
field  displacement)
Chapter 17
Section 2 Capacitance
Capacitors and Charge Storage
• A capacitor is a device that is used to store electrical
potential energy.
• Capacitance is the ability of a conductor to store
energy in the form of electrically separated charges.
• The SI units for capacitance is the farad, F, which
equals a coulomb per volt (C/V)
Chapter 17
Section 2 Capacitance
Capacitors and Charge Storage, continued
• Capacitance is the ratio of charge to potential
difference.
Q
C
V
magnitude of charge on each plate
capacitance =
potential difference
Chapter 17
Section 2 Capacitance
Capacitance
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Visual Concept
Chapter 17
Section 2 Capacitance
Capacitors and Charge Storage, continued
• Capacitance depends on the size and shape of a
capacitor.
• Capacitance for a Parallel-Plate Capacitor in a
Vacuum
A
C  0
d
capacitance = permittivity of a vacuum 
area of one of the plates
distance between the plates
 0  permittivity of the medium  8.85  10 C /N  m
–12
2
Chapter 17
Section 2 Capacitance
Capacitors in Keyboards
Chapter 17
Section 2 Capacitance
Parallel-Plate Capacitor
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Visual Concept