EM SPECTRUM

• The Electromagnetic Spectrum is a range of frequencies used for various purposes.
• The electromagnetic spectrum is the complete spectrum (or continuum) of all forms of “light”.
• An electromagnetic wave consists of electric and magnetic fields which vibrate, making waves.
• The electromagnetic spectrum progression from the waves of lowest frequencies to the waves of highest frequencies.
• The different types of electromagnetic waves are defined by the amount of energy carried by/possessed by the photons (bundles of wave energy).
• The energy of a photon is given by the equation: E = hf where h is the Planck’s Constant (6.63 x 10^-34 J/s) and f is the frequency of the EM wave.
• The gamma rays have photons of high energies while radio waves have photons with the lowest energies.
• The electromagnetic spectrum consists of radio waves, microwaves, infrared, visible light, ultraviolet, x-ray, and gamma rays.
• Properties of electromagnetic waves include speed, frequency and wavelength.
• Speed (v), frequency (f) and wavelength (λ) are related in the formula: v = f x λ.
• All light waves travel at a speed of 3 x 10^8 m/s in a vacuum.
• The electromagnetic spectrum consists of all parts traveling at the same speed.
• Frequency describes the number of waves that pass a fixed place in a given amount of time.
• Frequency is the number of waves that pass a fixed point in unit time; also, the number of cycles or vibrations undergone during one unit of time by a body in periodic motion.
• Frequency is usually measured in the hertz unit, named in honor of the 19th-century German physicist Heinrich Rudolf Hertz.
• Wavelength is the distance between corresponding points of two consecutive waves.
• As wavelength decreases, frequency will increase.
• Electromagnetic wave characteristics: short wavelengths have a high frequency, long wavelengths have a low frequency.
• High frequency waves have high energy, low frequency waves have low energy.
• Terrestrial Communication: Microwaves are used to transmit television news coverage from mobile broadcast vehicles back to the station.
• A cell phone is a radio transmitter and receiver that uses microwaves.
• Each cell has its tower that receives and sends microwave signals.
• The Electromagnetic Spectrum: Microwaves are part of the electromagnetic spectrum which also includes infrared radiation, visible light, ultraviolet radiation, and X-rays.
• Microwave Oven: Foods absorb certain microwave frequencies very strongly, causing the water molecules within the food to agitate, producing heat that cooks it.
• Infrared Radiation: Invisible electromagnetic waves that are detected as heat, can be detected with special devices such as night goggles, used in heat lamps, and have higher energy than microwaves but lower than visible light.
• Infrared Radiation: Infrared radiation lies beyond the red end of the visible light and is emitted by all objects, with shades of blue and green indicating colder temperatures and red and yellow indicating warmer temperatures.
• Infrared photographs taken from a satellite with special films provide useful details of the vegetation on the Earth’s surface.
• Infrared scanners are used to show the temperature variation of the body and for medical diagnosis.
• Infrared remote controls are used in TVs, video, cassette recorders and other electronic appliances.
• Some night-vision goggles use IR.
• Some autofocus cameras have transmitter that sends out infrared pulses.
• Visible Light: The portion of the electromagnetic spectrum that human eyes can detect, known as the visible spectrum, includes ROY G BIV (red, orange, yellow, green, blue, indigo, violet), with red having the lowest frequency and violet the highest.
• Ultraviolet Radiation: UV radiation has shorter wavelengths than the visible light, is higher in energy, and is used in UV lamps to check the signature on a passbook and identify fake banknotes.
• Ultraviolet Radiation: UV radiation is also used in sterilizing water from drinking fountains and some washing powder contains fluorescent chemicals that glow in sunlight.
• Ultraviolet Radiation: UV radiation activates vitamin D in the skin and gives us a tanning effect, but it can burn the skin and hurt our eyes and may cause skin cancer.
• X-Rays: X-rays are produced using an X-ray tube and are emitted when a fast moving electrons hit a metal target, discovered by Wilhelm Conrad Roentgen.
• X-Rays:Long wavelength X-rays can penetrate the flesh but not the bones and are used in X-ray photography to help doctors in diagnosing bone fractures and tumors.
• Short wavelength X-rays can penetrate even through metals and are used in industry to inspect welded joints for faults.
• Gamma Rays: Gamma rays are the highest energy, have the shortest wavelength, are emitted by stars and some radioactive substances, blocked from Earth’s surface by atmosphere and thick concrete and Pb, and used to treat cancer through radiotherapy.
• Radio waves are used to transmit sound and picture information over long distances.