Light Ken Rogers Miami Killian

Electrons move about the nucleus in energy levels. 3rd Energy Level 2nd Energy Level 1st Energy Level 1st 2nd 3rd

These energy levels surround the nucleus of the atom.

The electron absorbs energy and moves to a higher energy level. When energy is added to an atom, it causes electrons to move further away from the nucleus where the electrons have more energy. This step is called absorption. Energy level 3 The electron absorbs energy and moves to a higher energy level. energy level 2 energy level 1

When the electron falls back down to a lower energy level, the electron loses the energy it previously absorbed. This step (where the electron gives back its absorbed energy) is called emission. Energy level 3 It emits this energy in the form of a photon of light or radiant energy. energy level 2 energy level 1

Electromagnetic waves are produced by the movement of electrons within the atom. These waves are also called "electromagnetic radiation" because they radiate from the electrically charged particles. They travel through empty space as well as through air and other substances.

Scientists have observed that electromagnetic radiation has a dual "personality." Besides acting like waves, it acts like a stream of particles (called "photons") that have no mass. The photons with the highest energy correspond to the shortest wavelengths.

a) longer wavelength b) shorter wavelength

Measuring wavelength. . . . the distance from peak to peak or trough to trough is one way scientists measure the length of a wave. lambda peak to peak l trough to trough l

Electromagnetic Spectrum Visible Microwave X-Rays IR Gamma Rays UV Radio 400 nm 700 nm

Electromagnetic Spectrum Wavelength in meters 103 1 1 – 10-3 10-3 – 10-6 8x10-7-4x10-7 3x10-7- 10-8 10-8 – 10-12 10-12 Radio Microwave Infrared Visible Ultraviolet X-Ray Gamma Ray About the size of: Grains of sugar Protozoans Bacteria Molecules Atoms Atomic nuclei Buildings

wavelength, l = the distance between similar parts of the waves frequency (f or n) = the number of waves per second (also called Hertz or cycles per second) as the wavelength gets smaller (more crowded together) the frequency (# of waves) gets larger.

Count the number of waves that go by. To see that relationship, watch as we race these two light waves pass the red line. Count the number of waves that go by. The shorter the wavelength, the higher the frequency. l 8 The greater the wavelength, the lower the frequency. l 3

This is an inverse proportion which is equal to a constant. The equation is: wavelength times frequency equals a constant or l . f = c the value of the constant, c is 3.00 x 108 m/s and is the speed of light. so, l . f = 3.00 x 108 m/s

Example: All FM radio stations broadcast in megaHertz (1 x 106 waves/s). Coast FM, 97.3 on the FM dial, broadcasts 97.3 megaHertz or 97.3 x 106/s. What is the wavelength (distance between waves) for this frequency of radio waves? l . f = c l . f = 3.00 x 108 m/s l . 97.3 x 106/s = 3.00 x 108 m/s l = 3.00 x 108 m/s 97.3 x 106/s = 3.08 m

The energy that a photon of light possesses is a function of (depends on) its frequency. The more waves light has, the more energy it has. Or, the higher the frequency, the higher the energy. This is a direct proportion. The equation is: Energy of light = h . f or E = h . f where h (Planck’s constant) is 6.63 x 10-34 joule . s

Example: What is the energy of a single photon of X-ray which has a frequency of 2.00 x 1018/s? E = h . f E = 6.63 x 10-34 joule . s . f E = 6.63 x 10-34 J . s . 2.00 x 1018/s E= 1.33 x 10-15 J (per photon)

Bright line emission spectrum for hydrogen Bright line emission spectrum for sodium Link

Emission spectrum of hydrogen Hydrogen gas in glass tube Glass Prism