Great Ideas in Science: Lecture 4 Electricity and Magnetism

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Great Ideas in ScienceLecture 4Electricity and
Magnetism

• Professor Robert Hazen
• UNIV 301

Great Idea Electricity and magnetism are two
different aspects of one Force the
electromagnetic force.
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Electricity and magnetism are two aspects of the
same force.

• All magnets have both north and south poles
• Static electricity is manifest as a force between
  charged objects
• Electricity produces magnetic effects
• Moving magnets produce electricity

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Tonights Outline

• Natures Other Forces
• Magnetism
• Static Electricity
• Batteries and Electric Circuits
• Magnetic Effects from Electricity
• Electrical Effects from Magnetism
• Electromagnetic Radiation

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Magnetism

• Magnetic Force
• Natural magnetic minerals
• Earth is a giant magnet
• Used in navigation
• William Gilbert
• All magnets are dipoles
• Like repels, unlike attracts
• Earth is a dipole magnet
• Magnetic Field

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Magnetism at Different Scales

• Northern Lights
• Magnetic Bacteria

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Static Electricity

• Newtons First Law
• Greeks Observations
• Electrical charge
• Electricity
• Static electricity
• Two kinds of charge
• Opposites attract
• Like repels

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Benjamin Franklin, ca.1750

• Benjamin Franklin single electrical fluid
• Transfer of electrons
• Positive and negative charges
• Atomic structure

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Lightning

• Lightning occurs when the negatively-charged
  clouds interact with the positive charged ground

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Lightning

• Lightning occurs when the negatively-charged
  clouds interact with the positive charged ground

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The Lightning Rod

• Electrons are conducted harmlessly
• from clouds into the ground

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Coulombs Law, ca.1785
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Coulombs Law, ca.1785

• Charles Coulomb
• Experiments
• Coulombs Law
• Force is related to charge and distance
• 1 Coulomb 6.3 x 1018 electrons

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Force of Electricity vs. Gravity

• Coulombs Law
• Fe ke(q1 X q2)/d2
• Gravitational Force
• Fg kg(m1 X m2)/d2

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The Electrical Field

• The force felt by a charge located at a
  particular point
• Differs from the magnetic dipole field

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Frogs and Animal Electricityca. 1790
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Frogs and Animal Electricityca. 1790
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Alessandro Voltas Response (ca.1800)
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Alessandro Voltas Response (ca.1800)
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The Battery
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The Battery
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Three Parts of an Electric Circuits

1. Source of electrical energy
2. Closed path
3. Device to use electrical energy

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Electric Circuits
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Electric Circuits
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Two Kinds of Electric Circuits

• Series circuit vs. parallel circuit

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Ohms Law

• Flow of Electricity
• Current (amps)
• 1 amp1 coulomb/sec
• Voltage (volts)
• Amount of power in circuit
• Electrical Resistance (ohms)
• Ohms Law
• Current is directly proportional to voltage and
  inversely proportional to resistance
• Equation
• Load
• Equation

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Hans Christian Oersted, 1820
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The Electromagnet
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Magnetic Effects from Electricity
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Magnetic Effects from Electricity
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The Electric Motor

• North and South poles flip during rotary motion.

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The Electric Motor

• North and South poles flip during rotary motion.

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Michael Faraday, 1831Electrical Effects from
Magnetism
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Michael Faraday, 1831Electrical Effects from
Magnetism

• Electromagnetic induction
• Electrical fields and currents can be produced by
  changing magnetic fields

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Electric Generators

• Move a coil of wires next to magnets to create
  electricity
• Car alternator
• Turbines (power plants)
• Wind
• Water
• Steam - Coal/Nuclear power plants

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James Clark Maxwell, 1855
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Maxwells Laws, 1855

• Four equations describe the behaviors of
  electricity and magnetism
• 1. Coulombs Law of static electricity
• 2. All magnets have both north and south poles
• 3. Electricity produces magnetic effects
• 4. Moving magnets produce electricity
• These equations lead to prediction of waves
• 1. Waves travel 186,000 miles per second
• 2. Light is a consequence of electricity and
  
• magnetism switching back and forth

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The Electromagnetic Spectrum

• Maxwells equations predict more waves
• Hertz discovers radio waves