Electromagnetic Radiation Unit 4 Section B The Electromagnetic

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

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=λν Note: c= speed of light, λ=wavelength, v=frequency

Practice Problem #1 • A certain green light has a frequency of 6. 26 x 1010 Hz. The speed of light is 3. 00 x 108 m/s. What is the wavelength? ▫ c=λv ▫ Hz = 1/s ▫ λ = c/v = 3. 00 x 108 m/s 6. 26 x 1010 Hz = 4. 79 x 10 -3 m

Practice Problem #2 • Violet light has a wavelength of 4. 10 x 10 -7 m. The speed of light is 3. 00 x 108 m/s. What is the frequency of the light? ▫ λ = 4. 10 x 10 -7 m ▫ c = 3. 00 x 108 m/s ▫ v=? • C=λν ▫ v = c / λ = 3. 00 x 108 m/s 4. 10 x 10 -7 m = 7. 32 x 1014 1/s or Hz