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Great Ideas in Science: Lecture 4 Electricity and Magnetism

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Great Ideas in Science: Lecture 4 Electricity and Magnetism Professor Robert Hazen UNIV 301 Great Idea: Electricity and magnetism are two different aspects of one – PowerPoint PPT presentation

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Title: Great Ideas in Science: Lecture 4 Electricity and Magnetism


1
Great Ideas in Science Lecture 4 Electricity and
Magnetism
  • Professor Robert Hazen
  • UNIV 301

Great Idea Electricity and magnetism are two
different aspects of one Force the
electromagnetic force.
2
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

3
Tonights Outline
  • Natures Other Forces
  • Magnetism
  • Static Electricity
  • Batteries and Electric Circuits
  • Magnetic Effects from Electricity
  • Electrical Effects from Magnetism
  • Electromagnetic Radiation

4
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

5
Magnetism at Different Scales
  • Northern Lights
  • Magnetic Bacteria

6
Static Electricity
  • Newtons First Law
  • Greeks Observations
  • Electrical charge
  • Electricity
  • Static electricity
  • Two kinds of charge
  • Opposites attract
  • Like repels

7
Benjamin Franklin, ca.1750
  • Benjamin Franklin single electrical fluid
  • Transfer of electrons
  • Positive and negative charges
  • Atomic structure

8
Lightning
  • Lightning occurs when the negatively-charged
    clouds interact with the positive charged ground

9
Lightning
  • Lightning occurs when the negatively-charged
    clouds interact with the positive charged ground

10
The Lightning Rod
  • Electrons are conducted harmlessly
  • from clouds into the ground

11
Coulombs Law, ca.1785
12
Coulombs Law, ca.1785
  • Charles Coulomb
  • Experiments
  • Coulombs Law
  • Force is related to charge and distance
  • 1 Coulomb 6.3 x 1018 electrons

13
Force of Electricity vs. Gravity
  • Coulombs Law
  • Fe ke(q1 X q2)/d2
  • Gravitational Force
  • Fg kg(m1 X m2)/d2

14
The Electrical Field
  • The force felt by a charge located at a
    particular point
  • Differs from the magnetic dipole field

15
Frogs and Animal Electricity ca. 1790
16
Frogs and Animal Electricity ca. 1790
17
Alessandro Voltas Response (ca.1800)
18
Alessandro Voltas Response (ca.1800)
19
The Battery
20
The Battery
21
Three Parts of an Electric Circuits
  1. Source of electrical energy
  2. Closed path
  3. Device to use electrical energy

22
Electric Circuits
23
Electric Circuits
24
Two Kinds of Electric Circuits
  • Series circuit vs. parallel circuit

25
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

26
Hans Christian Oersted, 1820
27
The Electromagnet
28
Magnetic Effects from Electricity
29
Magnetic Effects from Electricity
30
The Electric Motor
  • North and South poles flip during rotary motion.

31
The Electric Motor
  • North and South poles flip during rotary motion.

32
Michael Faraday, 1831 Electrical Effects from
Magnetism
33
Michael Faraday, 1831 Electrical Effects from
Magnetism
  • Electromagnetic induction
  • Electrical fields and currents can be produced by
    changing magnetic fields

34
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

35
James Clark Maxwell, 1855
36
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

37
The Electromagnetic Spectrum
  • Maxwells equations predict more waves
  • Hertz discovers radio waves
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