1. Chapter 15

2. Waves in Space  One thing that all the forms of electromagnetic radiation have in common is that they can travel through empty space. This is not true of other kinds of waves; sound waves, for example, need some kind of material, like air or water, in which to move.

3.  Magnetic Fields  A magnetic field exerts a force on other magnets, causing them to line up along the direction of the magnetic field. Electric Fields  The electric field surrounding a charged particle exerts a force on all other charged particles in the field.

4.  A moving charged particle is surrounded by an electric field and a magnetic field.  As a charged particle moves up and down, it produces an electromagnetic wave.  Electromagnetic waves are produced by charged particles, such as electrons, that move back and forth or vibrate.

5.  As a charged particle vibrates by moving up and down or back and forth, it produces changing electric and magnetic fields that move away from the vibrating charge in many directions.

6.  Electromagnetic waves have a wavelength and a frequency. 1. One complete vibration of the charged particle up and down creates one wavelength in an electromagnet. 2. The number of wavelengths that pass by a point in 1 second is the frequency of the electromagnetic wave.

7.  Radiant energy- energy carried by an electromagnetic wave.  The amt. of energy carried by an electromagnetic wave is determined by its frequency.  The higher the frequency, the more energy the EM wave has.  Electromagnetic waves travel at the speed of light, 300,000 km/s, in space

8.  The difference between a wave and a particle might seem obvious  a wave is a disturbance that carries energy, and a particle is a piece of matter.  However, in reality the difference is not so clear.  In 1887, Heinrich Hertz found that by shining light on a metal, electrons were ejected from the metal.  Hertz found that whether or not electrons were ejected depended on the frequency of the light and not the amplitude. 

9.  Because the energy carried by a wave depends on its amplitude and not its frequency, this result was mysterious.  Years later, Albert Einstein provided an explanation  electromagnetic waves can behave as a particle, called a photon, whose energy depends on the frequency of the waves.  Because electromagnetic waves could behave as a particle, others wondered whether matter could behave as a wave.

10.  If a beam of electrons were sprayed at two tiny slits, you might expect that the electrons would strike only the area behind the slits, like the spray paint.

11.  Instead, it was found that the electrons formed an interference pattern.  This type of pattern is produced by waves when they pass through two slits and interfere with each other.

12.  The electromagnetic spectrum is the complete range of electromagnetic waves placed in order of decreasing frequency.

13.  Radio Waves have the lowest frequency and carry the least energy. (wavelength longer than 0.3 m)  AM and FM radio signals and T.V. signals are types of radio waves; they can be sent with radio waves using a transmitting and receiving antenna. a.One way to make radio waves is to make electrons vibrate up and down in a piece of metal called an antenna.

14. a.The radio waves from a transmitting antenna can cause electrons in another piece of metal, such as a receiving antenna, to move up and down, creating an alternating current. b.. The current can be used to produce sound from a loudspeaker, allowing for the transmission of music, television shows, and telephone signals.

15.  Microwaves have a higher frequency and shorter wavelength than radio waves; they are used for some phone calls and to heat food. (wavelengths b/w about 0.3 m and 0.001 m)  Radar uses electromagnetic waves to locate objects by measuring the time it takes for the waves to reach the object, be reflected, and return.

16.  Infrared Waves have wavelengths between one thousandth and 0.7 millionths of a meter and feel warm or hot. 1. Infrared detectors sense objects that are warmer or colder than their environment; TV and VCR remotes also use I.R. waves. 2. Some animals, such as piranhas and rattlesnakes, can detect I.R. waves, which helps them find prey

17.  Visible Light has wavelengths between 0.7 and 0.4 millionths of a meter. 1. what you see as different colors are EM waves of different wave lengths. 2. Red light has the longest wavelength (low freq.); blue light has the shortest wavelength (high freq.). ROYGBIV

18.  Ultraviolet Radiation is higher frequency and has shorter wavelength than visible light. 1. Too much exposure to ultraviolet radiation from the Sun can cause sunburn and other health problems. 2. Since U.V. radiation can kill cells, it is sometimes used to sterilize equipment. 3. The Ozone Layer in Earth’s upper atmosphere helps protect the surface by absorbing much of the Sun’s U.V. radiation. Ultraviolet Light Box

19.  Much of the ultraviolet radiation arriving at Earth is absorbed in the upper atmosphere by ozone.  Ozone is a molecule that has three oxygen atoms and is formed high in the Earth’s atmosphere  Chemical compounds called CFCs, which are used in air conditioners and refrigerators, can react with ozone molecules and break them apart

21.  X Rays and Gamma Rays, with even higher frequencies than U.V., can go right through skin and muscles. 1. Too much exposure to X-rays or gamma rays can damage or kill cells. 2. X-rays are useful in Medical Diagnosis if used with appropriate precautions. 3. Gamma rays, which have the highest frequency, can be used to treat Cancerous Tumors and to kill bacteria in food.

22.  Radio Transmission : ◦ Radio stations change sound to EM waves & then your radio receiver changes the EM waves back to sound waves again.  How does a radio receive different stations? ◦ Each station broadcasts at a certain frequency which you tune in by choosing their frequency. ◦ Dividing the Radio spectrum

23. ◦ Carrier wave- the frequency of the EM wave that a station uses ◦ Microphones convert sound waves to a changing electric current or electronic signal containing the words & music. ◦ The modified carrier wave vibrates electrons in the station’s antennae creating a radio wave that travels out in all directions at the speed of light to your radio antennae.  What is AM radio? ◦ In AM amplitude changes but frequency does not. AM frequencies range from 540,000 Hz to 1,6000,000 Hz usually listed in kHz.  What is FM radio? ◦ In FM radio stations transmit broadcast information by changing the frequency of the carrier wave. The strength of FM waves is always the same and is in megahertz. Mega=million

24. pressure modulation (sound) electromagnetic wave modulation Amplitude Modulation (AM) uses changes in the signal strength to convey information Frequency Modulation (FM) uses changes in the wave’s frequency to convey information

25.  Television: ◦ Uses radio waves to send electronic signals in a carrier wave. ◦ Sound is sent by FM; color and brightness is sent at the same time by AM signals  What is a cathode-ray tube? ◦ There are 3 types of spots, red, green and blue. The electron beams move back and forth across the screen. ◦ The signal from the TV station controls how bright each spot is. Three spots together can form any color. ◦ You see a full color image on the TV.

26.  Telephones ◦ Sound waves  microphone  electric signal  radio waves  transmitted to and from microwave tower  receiver  electric signal  speaker  sound wave

27.  How do cordless phones work? ◦ Cell phones and cordless telephones are transceivers, device that transmits one signal & receives another radio signal from a base unit. ◦ You can talk and listen at the same time because the two signals are at different frequencies.  How do pagers work? ◦ A pager is a small radio receiver with a phone number. A caller leaves a message at a terminal with a call-back number. ◦ At the terminal, the message is turned into an electronic signal transmitted by radio waves. ◦ Newer pagers can send and receive messages.

28.  Communications Satellites ◦ Thousands of satellites orbit Earth. A radio or TV station sends microwave signals to the satellite which amplifies the signal and sends it back to a different place on Earth. Satellite uses dif freq to send & receive.  Global Positioning System  GPS is a system of 24 satellites, ground monitoring stations and portable receivers that determine your exact location on Earth. GPS receiver measures the time it takes for radio waves to travel from 4 different satellites to the receiver. The system is owned and operated by the US Dept of Defense, but the microwaves can be used by anyone.