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

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

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 * 10-34 J*s

The Sun at Different Wavelengths of Radiation Section 4 Electromagnetic Waves Chapter 20 The Sun at Different Wavelengths of Radiation Insert High-Res image from TR113

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 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

The Electromagnetic Spectrum Section 4 Electromagnetic Waves Chapter 20 The Electromagnetic Spectrum Insert High-Res image from TR114