1. Electromagnetic Induction
Electromagnetic Waves

2. 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

3. 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

4. Propagation of Electromagnetic Waves

5. Propagation of Electromagnetic Waves
Electric and magnetic forces are aspects of a single force
Electromagnetic force
One of four fundamental forces in the universe
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

6. 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
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
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 * J*s

7. The Sun at Different Wavelengths of Radiation
Section 4 Electromagnetic Waves
Chapter 20
The Sun at Different Wavelengths of Radiation
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8. 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

9. 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

10. Electromagnetic Spectrum
X-Rays – high energy radiation
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

11. The Electromagnetic Spectrum
Section 4 Electromagnetic Waves
Chapter 20
The Electromagnetic Spectrum
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