Transcript SCI 111 - Onondaga Community College

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
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
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.
2
Force “Fields”
• Charges surrounded by electric fields
• Fields and charges inseparable
• Fields act on other charges.
Electric Potential (V)
Equation 6.3
A Volt is a Joule / Coulomb
Fig 6.8
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].
The Nature of Current
(3 Fundamental Conclusions ; see Fig 6.12 caption)
Fig 6.12
Fig 6.14
Electric Circuits
Fig 6.10
DC versus AC
Direct current (DC)
• Charges move in one
direction
• Batteries ; Solar Cells
How Stuff Works Homepage
Alternating current (AC)
• Charges rapidly change
directions
• Household circuits ;
Transformers.
FSU Homepage
Electrical Resistance (R)
Electrical Power and Work
Power in circuits
Electric bills
Cost of operating these items?
First: Determine how many Watts (P=IV)
Then:
Household Circuits and Safety
Circuit Breaker
• Three-Pronged Plug
• Polarized Plugs
• GFCI
Magnetism
A Property of Electricity
Magnetic Poles and Fields
Fig 6.19
No matter how you cut it,
it keeps coming up a “dipole”
Fig 6.20
Earth’s Magnetic Field
Fig 6.22
Fig 6.21
Magnetic
Declination
Electric Currents and Magnetism:
Current Loops
Fig 6.27
Fig 6.25
Current Loops:
Basis of a Solenoid
Note: Magnetic field is
like that of a bar magnet.
Electromagnets
Widely used “device”
Electric Meters
Galvanometer
Fig 6.28
Electric Switches:
Relays and Solenoid Switches
Fig 6.29
Electromagnets
Other Uses?
Telephones and Speakers
Electric Motors
Fig 6.30
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
Step-down
Fig 6.34
Fig 6.35
Step-down
Step-up
Step-up
Next: Exam 2