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Chapter 9.1 Notes Electromagnetic Waves Part 1 • A changing electric field can produce a changing Magnetic Field. • A changing magnetic field can produce a changing Electric Field • The combination of these two fields is what produces an Electromagnetic Wave. • Changing current can produce changing electric and magnetic fields that move away from an antenna at the speed of light and are called Electromagnetic Wave. • The energy is contained in the electric and magnetic field or in the electromagnetic wave and this energy is called Electromagnetic Radiation. • Electromagnetic waves travel at 300,000,000 m/s through a vacuum. • 300,000,000 m/s is the same speed as the speed of light. • We use the letter c to represent the speed of an electromagnetic wave. Speed of Light Demo • The speed in the air is approximately the same as the speed in a vacuum. • All electromagnetic waves travel at the same speed, but they can have different frequency and wavelength. • Equation for wavelength and frequency = speed = wavelength x frequency • c = λƒ • If our frequency is 1200 H, what is the wavelength? • c = λƒ • c = 300,000,000 m/s • 300,000,000 m/s = λ x 1200 H • 300,000,000 / 1200 = λ • Hertz = 1/s so the seconds cancels and leaves meters only. • λ = 250,000 m • The wavelength of a wave is the distance between peak of the electric field or magnetic field in the wave. • The frequency is the rate at which peaks pass a stationary point. • Wavelengths of electromagnetic waves range from millions of meters to as short as .0000000000000016 meters. • The range of wavelengths and frequencies of electromagnetic waves is called the electromagnetic spectrum. • The electromagnetic spectrum is divided into bands, based on sizes of the wavelengths of electromagnetic waves. • Radio Waves are the longest electromagnetic waves, some as long as several thousand kilometers. • • • • • • List the electromagnetic bands in order: Longest 1 Radio Waves 2 Microwaves 3 Light Waves 4 X Rays 5 Gamma Rays Shortest 6 Cosmic Rays •Light is broken into 3 categories: 1. Ultraviolet 2. Visible 3. Infrared • Radio waves are used to transmit radio and television signals. • Radio wavelengths can be less than 1 centimeter long or even hundreds of kilometers long. • At the radio or TV station, they have transducers that are used to convert sound into electric signals which creates an electromagnetic wave. • These radio waves are than transmitted in all directions from an antenna. • The waves travel to a receiving antenna and move at the speed of light (300,000,000 m/s). • At the receiving antenna, there is another transducer that changes the electromagnetic wave back into sound. • Each type of radio waves has a different wavelengths. For example, waves from a radio station are longer than waves emitted by your cell phone. • Microwave radiation has shorter wavelengths and higher frequencies than radio waves. • Microwave wavelengths range from approximately one millimeter (the thickness of a pencil lead) to thirty centimeters (about one foot). • Microwaves are used in telecommunication. They carry information from point to point on the Earth, or from Earth to satellites. • Microwaves are also used in radar systems to detect and track moving objects. • The direction of the reflected wave can be measured to locate the object. • The reflected wave frequency is changed if the object is moving and this change can be measured and used to determine the object’s speed. • In a microwave, the electromagnetic waves that are generated are tuned to frequencies that can be absorbed by water molecules. Microwave Demos • Lightbulb • CD • Soap