Aurora Borealis From MichiganTech page http:www'geo'mtu'eduweatheraurora

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Aurora Borealis From MichiganTech page
http//www.geo.mtu.edu/weather/aurora/
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Aurora Borealis From MichiganTech page
http//www.geo.mtu.edu/weather/aurora/
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Electric Charge

• Demo balloon
• Charging by rubbing what happens?
• Electrons and protons in atoms.
• Microscopic view of charging
• Moving charges electric current

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Conductors and Insulators

• Conductors need free (mobile) charges
• In metals there are free electrons
• Insulators have all charges firmly bound (glass,
  most plastics)
• What about air and water?
• Semiconductors
• Superconductors
• Human body?

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Electric current
A connecting wire discharges plates
Charged Plates
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Notice that these plates before they were
connected had some energy stored in them. The
difference of electric potential between the
plates (voltage) is a measure of this potential
energy
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Voltage characterizes the electric energy sources
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Electric current
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Electric current
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Electric current
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Electric current
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• The higher voltage will push electrons faster
• How fast will depend on the material
• We call the quantity characterizing the material
  conductivity s
• The thicker rod of material will allow more
  electrons at the same voltage, the longer rod
  will need more voltage to create the same current
  so the current I flowing through the rod will be
• I sAV/d
• where A is a cross section area of the rod, d is
  its length and V is the voltage.
• Inverse of s is called resistivity ?
• ? 1/s

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Conservation of current
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Current the flow of charges.

• I q/t
• Unit ampere A
• What kind of charges?
• electrons, ions, holes

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Batteries
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Electric potential
Gravitational Potential Energy mgh Gravitational
Potential gh
Electrical potential Energy (E constant)
qEs Electrical potential Es
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• Some Typical Voltages
• Voltage Source (approx.)
• Thundercloud to ground 108 V
• High-voltage power line 106 V
• Power supply for TV tube 104 V
• Automobile ignition 104 V
• Household outlet 120 V
• Automobile battery 12 V
• Flashlight battery 1.5 V
• Resting potential across
• nerve membrane 10-1 V
• Potential changes on skin
• (EKG and EEG) 10-4 V

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Sources of electric potential

• Batteries
• Van de Graaff generator
• Power stations
• Alternators
• Wind generators
• Solar panels
• Piezoelectric materials

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When do we use electrical energy

• Some Voltage and 0 current?
• Some current and 0 voltage?
• Both non zero?

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Resistance

• Ohms Law
• The current flowing through the resistor is
  proportional to the potential difference
  (voltage)
• It is not a fundamental law
• Valid for ohmic devices mainly metallic
  conductors at constant temperature.
• Definition of resistance
• I V/R
• Unit of resistance ohm ? V/A

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Resistance

• Valid for ohmic devices mainly metallic
  conductors at constant temperature.