Electromagnetic
Induction
Electromagnetic Waves
Propagation of Electromagnetic Waves
• Electromagnetic waves have electric field and magnetic field components (at
right angles to each other)
• Radio waves have long wavelength, short frequency, and low energy
• Gamma rays have short wavelength, high frequency, and high energy
• Visible light is somewhere in the middle
• Faraday’s law of induction - A changing magnetic field can induce a current
• Coulomb’s law – electric field lines flow from positive to negative charges
• Magnetic fields lines are closed loops
• Ampère’s law – a magnetic field is created around a current-carrying wire
Propagation of Electromagnetic Waves
• James Clerk Maxwell – developed equations to describe the
relationships between electric and magnetic fields in mid-1800s
• Combined the research of Coloumb, Faraday, and Ampère
• Hypothesized that a changing electric field should produce a magnetic field
• Inverse of Faraday’s law
• Described the wave formed by interactions of changing electric and
magnetic fields as an electromagnetic wave
• Predicted that light was electromagnetic
• Not confirmed until 1887 by Heinrich Hertz
• Transverse in nature – electric field is on one axis; magnetic field is on a second axis;
wave travels on a third axis
Propagation of Electromagnetic Waves
• Electromagnetic Waves
Propagation of Electromagnetic Waves
• Electric and magnetic forces are aspects of a single force
• Electromagnetic force
• One of four fundamental forces in the universe
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Gravitational
Electromagnetic
Weak Nuclear
Strong Nuclear
• The weak force and the electromagnetic force were once part of a single force
called the electroweak interaction
• Electromagnetic force obeys an inverse-square law
• Gets weaker based on the square of the distance from the source
• Similar to sound and gravity
Propagation of Electromagnetic Waves
• All electromagnetic waves are produced by accelerating charges
• Simplest source is an oscillating charged particle
• Wave propogates itself as the changing electric field generates a changing magnetic field which generates a
changing electric field
• Electromagnetic radiation – the transfer of energy associated with an electromagnetic wave;
it varies periodically and travels at the speed of light
• High energy electromagnetic waves behave like a particle
• Photon – a unit or quantum of light
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A particle of electromagnetic radiation that has zero mass and carries a quantum (amount) of energy
• Wave-particle duality of light – light has properties of both waves and particles
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Low-energy photons behave more wavelike
Energy of a photon = Plank’s (or Planck’s) constant * frequency
E=h*f
Plank’s constant = 6.63 * 10-34 J*s
Chapter 20
Section 4 Electromagnetic
Waves
The Sun at Different Wavelengths of Radiation
Electromagnetic Spectrum
• All electromagnetic waves are part of the electromagnetic spectrum
• The all travel at the same speed (3.00 * 108 m/s in a vacuum)
• Radio waves – longest wavelength, lowest frequency, lowest energy
• Long wavelength is ideal for transmitting energy over long distances
• TV and radio signals, radio telescopes
• Microwaves – microwave ovens, satellite signals, cellphones, radar,
telescopes
• Wavelengths from 30cm to 1mm
Electromagnetic Spectrum
• Infrared – experience infrared as heat
• Night vision goggles, remote controls, heat lamps, burglar-alarm systems
• 1mm to 700nm
• Visible light – what we see
• Wavelengths range from 700nm (red light) to 400nm (violet light)
• Ultraviolet (UV) – sunburns and suntans, sterilization of medical and
scientific equipment, black lights, forensic investigations, telescopes
• Certain materials fluoresce under ultraviolet
• Flowers, rocks, black light posters, body fluids
• Wavelengths from 400nm to 60 nm
Electromagnetic Spectrum
• X-Rays – high energy radiation
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Medical and dental applications – used to view hard tissues
Security checks to examine baggage at airports or government offices
X-Ray emissions give the evidence of black holes
Wavelengths from 60nm to .0001nm
• Gamma Rays – Very high energy
• Radiation therapy in cancer treatments
• Space telescopes
• Wavelengths less than .0001nm
Chapter 20
Section 4 Electromagnetic
Waves
The Electromagnetic Spectrum