Chapter 9.1 Notes Electromagnetic Waves Part 1

A changing electric field can produce a changing Magnetic Field.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, ,000,000 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 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