5.1: electromagnetic radiation

electromagnetic radiation

• many types, each with different wavelengths and frequencies
• frequency (ν): the number of waves that pass a fixed point in a second
  • measured in Hz (waves/second, cycle/second, 1/s, s-1)
• wavelength (λ): inversely related to frequency
  • waves are measured in meters (m) or nanometers (1m = 109 nm); nm are usually used in the visible region
  • measured from the peak of one wave to the peak of the next, or the trough of one wave to the trough of the next
• light in the visible range (colors) is the only type of electromagnetic radiation that the human eye can detect

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light

• light is composed of electromagnetic radiation
  • has wave-like properties and is characterized by wavelength, frequency, and speed
  • dependent on electronic structure (how the formation of electrons in an atom is) and electromagnetic radiation
• electromagnetic radiation travels in waves that have electric fields and magnetic fields perpendicular to each other
• the speed of light
  • variable =c, constant in a vacuum
  • c = 3.00 x 108 meters per second
  • c = λν
• divided into spectra which dictate different properties, namely whether the human eye can detect its presence and appearance in color

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matter vs. energy

• in the early twentieth century, matter and energy were viewed as fundamentally distinct
  • matter was composed of particles
  • energy was composed of waves
  • this later developed into the notion that energy existed in particles
• Planck then developed the theory that energy is quantized
  • particles of energy are called quanta (the single form of which is quantum)
  • relationship between energy and frequency: E=Hν
  • energy can behave as both waves and particles
  • Planck constant: constant h; 6.62 x 10^-34 joule-seconds
• frequency (ν) is the bridge between the two units

properties of energy

• quantized energy (detailed further in next note) is measured by Planck’s constant, units are quantum and photons
• energy of photon = Planck constant x frequency

properties of matter

• contain matter waves, or the wave characteristics present in material particles
• momentum describes the quantity mv (mass x velocity) of any object
• Heisenberg’s uncertainty principle posits that it is impossible for people to know simultaneously the exact momentum of an electron and its exact location in space
  • these cannot be measured at the same time, but estimations can be made to approximate one or the other

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