Chapter 6: Electricity

and Magnetism

Electric Charges

Fig 6.3

Electrostatic Charge

• Stationary charge confined to an object

• Charging mechanisms– Friction– Contact with a

charged object– Induction

• Stationary charge confined to an object

• Charging mechanisms– Friction– Contact with a

charged object– Induction

Electrical Conductors and Insulators

Measuring Electric Charge

• Unit of charge – Coulomb (C)– Equivalent to charge of 6.24x1018 electrons!– Fundamental metric unit – FYI: Equation 6.1

• Unit of charge – Coulomb (C)– Equivalent to charge of 6.24x1018 electrons!– Fundamental metric unit – FYI: Equation 6.1

Measuring Electrical Forces

Coulomb’s law• Relationship giving force

between two charges• Similar to Newton’s law

of gravitation but…• Ratio of “k” versus “G”

implies gravity weaker.

Coulomb’s law• Relationship giving force

between two charges• Similar to Newton’s law

of gravitation but…• Ratio of “k” versus “G”

implies gravity weaker.2

• Charges surrounded by electric fields • Fields and charges inseparable • Fields act on other charges.

• Charges surrounded by electric fields • Fields and charges inseparable • Fields act on other charges.

Force “Fields”

Electric Potential (V)

Fig 6.8

Equation 6.3

A Volt is a Joule / Coulomb

Electric Current (I)

• Flow of charge• Reason for charge flow:

– Potential differences (voltage)

• Charge per unit time– Thus, a “rate”

• Units?– Coulomb per second [C/s] – Amperes [Amps].

• Flow of charge• Reason for charge flow:

– Potential differences (voltage)

• Charge per unit time– Thus, a “rate”

• Units?– Coulomb per second [C/s] – Amperes [Amps].

The Nature of Current(3 Fundamental Conclusions ; see Fig 6.12 caption)

Fig 6.14Fig 6.12

Electric Circuits

Fig 6.10

DC versus AC

Alternating current (AC)Alternating current (AC)Direct current (DC)Direct current (DC)

How Stuff Works Homepage FSU Homepage

• Charges rapidly change directions

• Household circuits ; Transformers.

• Charges rapidly change directions

• Household circuits ; Transformers.

• Charges move in one direction

• Batteries ; Solar Cells

• Charges move in one direction

• Batteries ; Solar Cells

Electrical Resistance (R)

Electrical Power and Work

Power in circuitsElectric bills

Cost of operating these items?

First: Determine how many Watts (P=IV)Then: First: Determine how many Watts (P=IV)Then:

Household Circuits and Safety

Circuit Breaker

• Three-Pronged Plug• Polarized Plugs• GFCI

• Three-Pronged Plug• Polarized Plugs• GFCI

MagnetismA Property of Electricity

Magnetic Poles and Fields

Fig 6.20Fig 6.19

No matter how you cut it,it keeps coming up a “dipole”

Earth’s Magnetic Field

MagneticDeclinationMagnetic

Declination

Fig 6.21

Fig 6.22

Electric Currents and Magnetism: Current Loops

Fig 6.25

Fig 6.27

Current Loops: Basis of a Solenoid

Note: Magnetic field is like that of a bar magnet.

ElectromagnetsWidely used “device”

GalvanometerFig 6.28

Electric Meters

Fig 6.29

Electric Switches:Relays and Solenoid Switches

ElectromagnetsOther Uses?

Fig 6.30

Telephones and SpeakersElectric Motors

Fig 6.31

Electromagnetic Induction(to induce is to cause)

Fig 6.32

Generators

Fig 6.33

How does “power” get to your house?

Transformers

Fig 6.34

Fig 6.35

Step-down

Step-down

Step-up

Step-up

Next: Exam 2