Preview Statics Circuits Electricity and Magnetism Chapter 16 Section 1 Electric Charge.

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• Statics

• Circuits

• Electricity and Magnetism

Chapter 16 Section 1 Electric Charge

Section 1 Electric ChargeChapter 16

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.


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.

Click below to watch the Visual Concept.

Visual Concept


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

The Milikan Experiment

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.


Visual Concepts

Visual Concept

Chapter 16

Charging by Induction


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.

Section 2 Electric ForceChapter 16

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.

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 propor-tional to the magnitude of each charge and inversely proportional to the square of the distance between them.

Section 2 Electric Force

1 22

2

charge 1 charge 2electric force = Coulomb constant

distance

electric C

q qF k

r


Visual Concept

Chapter 16 Section 2 Electric Force

Superposition Principle

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 2 Electric Force

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.


Visual Concept


Electric Fields and Test Charges


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

2

2

charge producing the fieldelectric field strength = Coulomb constant

distance

C

qE k

r


Visual Concept


Calculating Net 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.


Visual Concept


Rules for Drawing Electric Field Lines


Visual Concept


Rules for Sketching Fields Created by Several Charges

Section 1 Electric PotentialChapter 17

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


Visual Concept

Chapter 17 Section 1 Electric Potential

Electrical Potential Energy


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:

V

PEelectric

q


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.

change in electric potential energy

potential differenceelectric charge

electricPEV

q


Visual Concept

Chapter 17 Section 1 Electric Potential

Potential Difference


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)

Section 2 CapacitanceChapter 17

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)


Capacitors and Charge Storage, continued

• Capacitance is the ratio of charge to potential difference.

magnitude of charge on each platecapacitance =

potential difference

QC

V


Visual Concept

Chapter 17 Section 2 Capacitance

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

–12 2

0

0

area of one of the platescapacitance = permittivity of a vacuum

distance between the plates

of the medium 8.85 10 C /N mpermittivity

AC

d

Chapter 17

Capacitors in Keyboards

Section 2 Capacitance


Visual Concept

Chapter 17 Section 2 Capacitance

Parallel-Plate Capacitor

Preview Statics Circuits Electricity and Magnetism Chapter 16 Section 1 Electric Charge.

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