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The Electromagnetic Spectrum and Photoelectric Effect

The Electromagnetic Spectrum and Photoelectric Effect

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The Electromagnetic Spectrum and Photoelectric Effect

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  1. The Electromagnetic Spectrum and Photoelectric Effect

  2. The Electromagnetic Spectrum • Quantum theory is based on how electrons interact with electromagnetic waves. • Electromagnetic waves are always present. Some are completely safe and some are dangerous. • Light • Radio • Microwave • Gamma

  3. The EM Spectrum

  4. Radio Waves • Longest wavelength, lowest frequency. • Information is carried by changing a property of the wave. • AM means Amplitude modulation • FM means frequency modulation • Energy of one photon of a radio wave cannot remove electrons, so they are not considered to be dangerous.

  5. Microwaves • Called microwaves because they have a wavelength of a micrometer. • Used by many cell phones and wireless devices to transmit information. • Used in microwave ovens to heat food. • Heat polar molecules the best. • Energy is not high enough to remove electrons so they are considered to be safe.

  6. Infrared Radiation • The energy we lose as heat leaves our bodies by infrared radiation.

  7. Visible Light • ROY G BIV • Red • Orange • Yellow • Green • Blue • Indigo • Violet

  8. Ultraviolet (UV) • Part of Sunlight • Can Cause DNA damage which may lead to cancer. • UV exposure causes increased aging by damaging collagen. • Melanin is the pigment that makes you look tan and is produced by your skin to try and reflect UV rays • Sunscreen can block UV rays. SPF tells you how powerful the protection is.

  9. X Rays • Used in medicine • Cannot travel through bones • Given contrast to see other systems • Continued exposure can damage DNA and lead to increased cancer rates.

  10. Gamma Rays • Radioactive Decay • They WILL cause cancer by mutating your genes • “CyberKnife” uses them to remove tumors. • Used to treat and kill cancer cells. • “Radiation” = Gamma Rays

  11. Photoelectric Effect

  12. It all starts with waves… • Electromagnetic rays hit an object (usually a metal) and electrons are not just move up energy levels, they are released.

  13. Then comes electricity… • The movement of the electrons causes the metal to become a conductor of electricity • It is a transformation of energy • From wave energy (EM Radiation) to electrical energy.

  14. Other Requirements • The wave has to be made of photons with high enough energy to remove the electron. • Minimum energy needed to remove an electron is called the threshold frequency. • If the photon is below the threshold frequency in energy it doesn’t matter how much light you shine on the object, nothing will happen. • Energy of the photon can be calculated with Einstein’s equations.

  15. When do we used this? • Solar Panels • Light from the sun causes electrons to be released. • The movement of electrons causes electricity to be produced.