Electromagnetic Radiation Unit 4, Section B

The Electromagnetic Spectrum Light is electromagnetic radiation (energy that exhibits wavelike behavior). Electromagnetic spectrum: Radio, Microwave, Infrared, Visible, Ultraviolet, X-Ray, Gamma Ray (long wavelength to short wavelength)

The Electromagnetic Spectrum 3

Types of Electromagnetic Radiation Radio Waves: longest wavelengths = lowest frequencies Used for wireless transmission of sound messages and other information Very High Frequency (VHF) – FM radio and TV Super Low Frequency (SLF) – communicate with submarines underwater Also, emitted by stars and gases in space and studied by astronomers to gather information about the universe.

Types of Electromagnetic Radiation (cont’d) Microwaves: between radio waves and infrared radiation Used for heating and cooking food Carry telephone and TV signals between stations on Earth and communication satellites Used in radar systems to track position and speed of various objects

Types of Electromagnetic Radiation (cont’d) Infrared Radiation: between microwaves and visible radiation aka Heat - invisible to naked eye but detected as warmth by the skin Used in night vision instruments, meteorology, telecommunications

Types of Electromagnetic Radiation (cont’d) Visible Radiation: red borders infrared and violet borders ultraviolet aka Light – visible to human eye and consists of a continuous spectrum of colors: ROYGBIV Visible radiation is emitted by everything from fireflies to light bulbs to stars ½ of Sun’s energy is released as visible radiation Essential for photosynthesis

Types of Electromagnetic Radiation (cont’d) Ultraviolet (UV) radiation: between visible radiation and x-rays Sun is a source of UV radiation – UV rays burn/tan our skin Over-exposure results in skin cancer, eye cataracts, and damage to body’s immune system Ozone layer naturally protects against the most harmful UV radiation emitted by the Sun

Types of Electromagnetic Radiation (cont’d) X-Rays: between UV radiation and Gamma Rays Used to generate images of the human body (bones, tissue, and teeth) Over-exposure can cause cancer and birth defects Hot gases in the universe emit X-rays

Types of Electromagnetic Radiation (cont’d) Gamma Rays: shortest wavelengths = highest frequencies Used to sterilize medical instruments and supplies which cannot be boiled Damages biological organisms by penetrating substances deeply Radioactive materials emit gamma rays Radon gas emits gamma rays Greatest generator is the Universe

Solar Radiation Most of the radiant energy emitted by the Sun is spread over a large portion of the electromagnetic spectrum: 45% is in the infrared (IR) region 46% is in the visible region 9% is in the ultraviolet (UV) region Less than 1% of solar radiation falls outside of these three regions

Properties of Light Speed of Light = Constant speed (c) of 3.0 x 108 m/s through a vacuum. Light consists of waves Wavelength () Crest to crest Trough to trough Between two identical points Frequency () # of waves that pass a given point in an assigned time Usually 1 second Hertz (Hz) = waves/second

Properties of Light (cont’d) Wavelength and frequency Inversely proportional Wavelength increases, frequency decreases c = λ ν Note: c= speed of light, λ=wavelength, v=frequency

Practice Problem #1 A certain green light has a frequency of 6.26x1010 Hz. The speed of light is 3.00 x 108 m/s. What is the wavelength? c = λ v Hz = 1/s λ = c/v = 3.00x108 m/s 6.26x1010 Hz = 4.79 x10-3 m

Practice Problem #2 Violet light has a wavelength of 4.10x10-7 m. The speed of light is 3.00 x 108 m/s. What is the frequency of the light? λ = 4.10x10-7 m c = 3.00 x 108 m/s v = ? C = λ ν v = c / λ = 3.00x108m/s 4.10x10-7 m = 7.32x1014 1/s or Hz