Classification of Electromagnetic Radiation

Transcription

1 Light and Energy Electromagnetic Radiation Radiant energy that exhibits wavelength-like behavior and travels through space at the speed of light in a vacuum. Example: The sun light, energy used in microwave oven, the x-rays used by doctors.

2 Classification of Electromagnetic Radiation

3 The Nature of Waves

4 Waves Waves have 3 primary characteristics: 1. Wavelength (λ) (lambda): distance between two consecutive peaks in a wave. 2. Frequency (ν) (nu): number of waves (cycles) per second that pass a given point in space. 3. Speed (c): speed of light is x 10 8 m/s. We will use 3.00 x 10 8 m/s.

5 Wavelength and frequency can be interconverted and they have an inverse relationship λ = c /ν OR λ ν = c ν = frequency (s -1 ) λ = wavelength (m) c = speed of light (m s -1 ) Wavelength is also given in nm (1 nm = 10-9 m) and Angstroms (Å) (1 Å = m). The frequency value of s -1 or 1/s is also called hertz (Hz) like KHz on the radio.

6 Atomic Spectrum of Hydrogen When H 2 molecules absorb energy, some of the H-H bonds are broken and resulting hydrogen atoms are excited. The excess energy is released by emitting light of various wavelengths to produce the emission spectrum of hydrogen atom. Continuous spectrum: Contains all the wavelengths of light. Line (discrete) spectrum: Contains only some of the wavelengths of light. Only certain energies are allowed, i.e., the energy of the electron in the hydrogen atom is quantized. E = hν = hc λ

7 (a) (b) A Continuous Spectrum (a) and A Hydrogen Line Spectrum (b) For the Hydrogen Spectrum: A Change between Two Discrete Energy Levels More Distance=More energy

8 ABSORPTION/EMISSION Electricity or heat in visible light out Electrical energy is absorbed and excites the electrons to higher energy levels. The electrons then emit (give off) energy in the form of visible light.

9 The size of the jump determines the type of energy produced: UV higher; visible medium; IR lower Energy 2 1 Ultra Violet Lyman Visible Balmer Infrared Paschen n

10 Neon lights Examples of Absorption/Emission Fireworks displays Toys Flame test and spectrum tubes

11 FLUORESCENCE UV light in visible light out Ultraviolet (UV) energy is absorbed and excites the electrons to higher energy levels. The electrons then emit (give off) energy in the form of visible light.

12 Examples of Fluorescence Black light posters Neon colored posters, product packages Laundry brighteners/whiteners Fluorescent dyes & inks Certain minerals/rocks

13 PHOSPHORESCENCE visible or UV light in time delay visible light out Visible and/or Ultraviolet (UV) energy is absorbed and excites the electrons to higher energy levels. The electrons then emit (give off) energy in the form of visible light with a time delay.

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15 Examples of Phosphorescence Glow in the dark stuff Zinc sulfide older glow-in-the-dark material doesn t last as long Strontium aluminate newer glow-inthe-dark material lasts much longer

16 CHEMI-/BIO- LUMINESCENCE chemical energy in visible light out Chemicals are mixed and the energy excites electrons. Instead of energy being released in the form of heat, the energy is released in the form of cool light. This is chemiluminesence. If this occurs in a living organism it is called bioluminescence.

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18 Examples of Chemi- and Bio- Light sticks Fireflies Many deep sea organisms Luminescence

19 TRIBOLUMINESCENCE mechanical energy in visible light out Mechanical energy excites the electrons in adhesive molecules, which then excite the electrons around nitrogen atoms in the air. The energy is then emitted in the form of visible light. (bandage example) In the case of wintergreen, the methyl salicylate molecules are fluorescent, and so the mechanical energy excites the electrons in the wintergreen flavoring.

20 Examples of Triboluminescence Bandage packages Crushing wintergreen candies

21 LASER Light Amplification by the Stimulated Emission of Radiation electrical energy in coherent light emitted The light produced is of a single phase and is combined to produce a coherent beam of light laser light.

22 LASERS Electrical energy is used to stimulate the electrons, and visible coherent light of a single phase is emitted.

23 Examples of Lasers Grocery store scanners Levels used in building Laser surgery