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 = 냕 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. Ultraviolet2. Visible3. 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