Ideas for Web Projects • • • • Biography of any scientist mentioned in the book High-energy Radiation (UV, X-ray, -ray) Noble Gases (properties, use, where can be found) Plate Tectonics (the concept, its history, modern view) • The Fate of the Sun • First Years of the Universe Lecture 12 Electromagnetic Waves • Types of electromagnetic waves • Wave properties Electromagnetic Waves A changing magnetic field generates an electric current electromagnetic induction. J.C.Maxwell proposed that a changing electric field has an associated magnetic field. Such a combined effect results in existence of electromagnetic waves, which can travel indefinitely in empty space (vacuum). Electromagnetic waves travel with the speed of light. Light in Everyday Life Light is a form of energy, radiative energy Light has color A prism split light into a spectrum (rainbow of colors) Light travels with a speed of c = 300,000 km/s Rainbow Properties of Light Light behaves as both a particle and a wave Light particles are called photons, which can be counted individually. Light is also an electromagnetic wave The wavelength is the distance between adjacent peaks of the electric or magnetic field 1 nm (nanometer) = 10–9 m 1μm (micron) = 10–6 m The frequency is the number of peaks that pass by any point each second, measured in cycles per second or Hertz (Hz). light demo Many Forms of Light The spectrum of light is called the electromagnetic spectrum Different portions of the spectrum are called: Gamma rays - the shortest wavelength light X rays - wavelengths shorter than ultraviolet The ultraviolet light - beyond the blue end The visible light - what we see with our eyes The infrared light - beyond of the red end of rainbow Radio waves - light with the longest wavelengths Electromagnetic spectrum Electromagnetic spectrum E=h E = energy = frequency h = Planck constant Interaction of Light and Matter • Emission (atomic spectra) • Absorption • Transmission (passing through) • Reflection (scattering) Other Wave Properties Refraction Change in a wave direction produced by a change in speed Interference Adding together of 2 or more waves of the same kind that pass by the same point at the same time Diffraction Ability of waves to bend around the edge of an obstacle Diffraction limit is the largest resolving power of an optical system. Summary Electromagnetic waves are fluctuations generated by moving electric charges. Visible light is only a small portion of the electromagnetic spectrum. Basic properties of electromagnetic waves include reflection, refraction, interference, and diffraction.