Electromagnet

Waves

ic

How do you think a bee locates a flower?

When a bee looks at a flower and youlook at the same flower, do both of yousee the same thing?

Do bees see all the same things we seewhen they look at a flower?

Some flowers have markings on them that areinvisible to humans. These markings are only seenin ultraviolet light.

1. Describe the nature of electromagnetic waves.

2. Explain how electromagnetic waves differ from other waves.

3. Explain how electromagnetic waves are produced.

4. Identify the regions of the electromagnetic spectrum.

5. Describe the uses of the electromagnetic waves of differentfrequencies.

6. Explain the relationship between wavelength and frequency.

7. Explain three ways by which luminous objects produce light.

8. Describe the particle nature of electromagnetic waves.

Objectives:

TYPES OF WAVESTYPES OF WAVES

Waves Waves are classified into different types according to their natures :

T ra ns ve rs e w a ve s L o ng itud ina l w a ve s

Mechanical w aves

T ra ns ve rs e w a ve s

Elec tromagnetic w aves

WA V E S

In 1879, a Scottish scientist named James Clerk Maxwell developed a mathematical description of Faraday’s “fields”.

(13 June 1831 – 5 November 1879)

Maxwell found that as electric and magnetic fields changed, they traveled together through space as a single wave, what we call today an electromagnetic wave. Maxwell’s mathematics even told him how fast that the waves moved.

1

It was Maxwell’s genius to see that light (which had always been a mystery anyway) must be made of these waving electric and magnetic fields.

Not only that, but Maxwell could see that there must be many other kinds of light — light invisible to our eyes and unknown to science.

German Scientist Heinrich Hertz first discovered Maxwell’s predicted radio waves in 1887. To capture those waves, Hertz used a wire loop.

2

Light has been described as a particle, as a wave and evenas a combination of the two.

The current model for light has incorporated aspectsof both particle and wave theories.

Not all light is visible to the human eye.

3,4

Electromagnetic waves carry no mass, but they do carry energy.

Electromagnetic waves are transverse waves and do not require a medium. This means that electromagnet waves can travelthrough a vacuum (no air).

Each electromagnetic wave emits a different level of energy.

5,6,7

Electromagnetic waves are vibrations of magnetic and

electric fields positioned at right angles to each other and

to the direction of the motion of the wave.

Red – electric fieldBlue – magnetic field

8

As the electric field increases, it induces an increasing magnetic field at right angles to it, and vice-versa.

The waves, in the absence of any intervening absorbing medium, propagate indefinitely.

Red – electric fieldBlue – magnetic field

Electromagnetic waves are distinguished by their unique wavelengths and frequencies.

In visible light, the difference in frequencies and wavelength account for different colors.

The difference in frequencies and wavelengths also distinguishes visible light from invisible electromagnetic radiation, such as X rays.

9,10,11

One way to measure the energy of an electromagnetic waveis by measuring its frequency.

Frequency refers to the number of vibrations created in aperiod of time.

In general, the higher the frequency, or number of waves, thegreater the energy of the radiation.

Wavelength and frequency are inversely related, meaning thegreater the length of the wave, the lower its frequency will be.

If the frequency is high, the wave must be shorter. Theshorter the wave the higher the energy.

12,13,14

In a vacuum, all electromagnetic waves travel at the speed oflight: 3.0 × 108 m/sec.

This quantity is called “the speed of light” but it really refersto the speed of all electromagnetic waves, not just visible light.

The relationship between frequency, wavelength and speed also holds true for light waves.

15

Electromagnetic waves exist in an enormous continuous range of frequencies.

They are organized in the electromagnetic spectrum according to their wavelength, from the shortest (gamma) to the longest (radio).

16

Types of electromagnetic waves along with their wavelengths and frequenciesare shown at the left.

Although specific ranges are shown in the table, the electromagnetic spectrum is, in reality continuous with no sharp division between one kind of wave and the next.

Radio Waves

It was discovered that radio waves could bounce off airplanes and end up right back where they started. This idea came to be called radar, which stands for radio detection and ranging.

Radio waves are the waves used to transmit information from the antenna of a broadcasting station to the antennae on your radio.

When you think of radio waves, do not confuse them with thewaves you hear coming out of your radio. A radio convertsradio waves into sound.

17,18

When radio waves are transmitted, one of two characteristicscan be varied – either the amplitude or the frequency.

The variation in the amplitude or frequency of a wave is calledmodulation. The setting on your radio indicates the type ofmodulation used to carry the information to your radio.

AM stands for amplitude modulation.

FM stands for frequency modulation.

19,20,21

AM radio waves have longer wavelengths than FM radio waveshave, they can bend around hills and buildings.

The shorter wavelength FM radio waves are blocked by largeobjects.

22

Sound transmitted by an AM radio station affects the carrier wave by changing the amplitude (height) of the carrier wave, as shown below.

Unfortunately, this type of modulation is subject to static interference from such things as household appliances — and especially from lightening storms.

23

FM is virtually immune to any type of external interference, it has a greater dynamic range, and it can handle sounds of higher and lower frequencies.

This is why music, with its much greater frequency range than the human voice, sounds better on FM radio.

FM radio works by changing the frequency of the carrier wave.

Note that when the carrier wave of FM radio is modulated with sound that the distance between the waves, or the frequency of the carrier wave, changes.  

24,25

What is the primary use for radio waves? Communication

Satellite Communication

Cordless Phones

26

WirelessCommunication

Microwaves are radio waves with the shortest wavelengthand the highest frequency.

Microwaves are used in cooking,

Communication

Radar

27,28

Infrared light lies between the visible and microwave portions of the electromagnetic spectrum. Infrared light has a range of wavelengths.

"Near infrared" light is closest in wavelength to visible light and "far infrared" is closer to the microwave region of the electromagnetic spectrum.

Since the primary source of infrared radiation is heat or thermal radiation, any object which has a temperature radiates in the infrared.

29,30,31

Far infrared waves are thermal. In other words, we experience this type of infrared radiation every day in the form of heat! The heat that we feel from sunlight, a fire, a radiator, a heat lamp or an electric burner.

Shorter, near infrared waves are not hot at all - in fact you cannot even feel them. These shorter wavelengths are the ones used by your TV's remote control.

32,33

A thermogram is a thermal image made from an infrared camera or other infrared device. Devices that make use of thermograms are able to display outlines of the subjects based on the amount of infrared radiation (which corresponds to the amount of heat) emitted by the body.

Applications for thermograms range from medical diagnostics to search and rescue devices. These are highly favored devices because of their non-invasive capabilities.

34,35

Night vision devices make use of infrared by either capturing the naturally emitted infrared radiation from the subjects or by using infrared light sources that are not as noticeable as visible light.

Devices like these are mostly used in the military.

36

Isaac Newton showed that light shining through a prism will be separated into its different wavelengths and will thus show the various colors of which visible light is comprised.

37

The separation of visible light into its different colors is known as dispersion.

Visible light waves are the only electromagnetic waves we can see. We see these waves as the colors of the rainbow.

Each color has a different wavelength.

38,39

Bluer light has shorter wavelength, higher frequency, and more energy.

Redder light has longer wavelength, lower frequency, and less energy.

When all the waves are seen together, they make white light.

40,41,42

Ultraviolet (UV) light waves are invisible to the human eye.

Scientists have divided the ultraviolet part of the spectrum into the three regions (Near UV, Far UV and Extreme UV) shown in the diagram above.

The three regions are distinguished by how energetic the ultraviolet radiation is, and by the "wavelength" of the ultraviolet light, which is related to energy.

43

Our Sun emits light at all the different wavelengths in electromagnetic spectrum, but it is ultraviolet waves that are responsible for causing our sunburns.

44

Though some ultraviolet waves from the Sun penetrate Earth's atmosphere, most of them are blocked from entering by various gases like Ozone.

Some days, more ultraviolet waves get through our atmosphere.

Scientists have developed a UV index to help people protect themselves from these harmful ultraviolet waves.

45

Astronomers have to put ultraviolet telescopes on satellites to measure the ultraviolet light from stars and galaxies - and even closer things like the Sun!

Uses of Ultraviolet Light

46

Ultraviolet light frequently used in security. For instance, currency, has invisible symbols on it that light up only in the presence of UV light. These are difficult for counterfeiters to copy.

46

Sensitive documents, such as driver's licenses, credit cards or passports, have invisible symbols on them that light up only in the presence of UV light.

46

Ultraviolet light has been implicated in multiple human diseases from skin cancer to cataracts to immune suppression.

Ultraviolet rays cause skin calls to produce vitamin D, which your body needs. However too much exposure is harmful.

47,48

The Earth's atmosphere is thick enough that virtually no X-rays are able to penetrate from outer space all the way to the Earth's surface.

49

X-rays were first observed and documented in 1895 by Wilhelm Roentgen, a German scientist who found them quite by accident when experimenting with vacuum tubes.

50

A week later, he took an X-ray photograph of his wife's hand which clearly revealed her wedding ring and her bones. The photograph electrified the general public and aroused great scientific interest in the new form of radiation.

Roentgen called it "X" to indicate it was an unknown type of radiation. The name stuck, although over Roentgen's objections.

When an X-ray picture of a part of your body is taken, the bonesabsorb the rays, but the soft tissues do not.

The picture that results shows the bones as white areas andthe soft tissue as black areas.

51,52

Despite their usefulness in medical diagnosis, X-rays are apotential health hazard. Exposure to body cells and tissues tolarge amounts of X-rays over a lifetime can cause defects in cells.

Lead absorbs almost all the X-rays that strike it. X-raytechnicians wear lead aprons to protect them from exposure.

53

Strong sources of X-rays have been detected deep in space.the sources are believed to be certain star formations.

In addition to these star formations, exploding stars are knownto give off most of their energy at the time of explosion inthe form X-rays.

Gamma rays are the electromagnetic waves with the highest frequency and the shortest wavelength.

Gamma rays have the highest energy of the electromagneticspectrum.

Certain radioactive materials and nuclear reactions emitgamma rays.

54,55,56

Most of the gamma radiation observed on Earth comefrom radioactive substances.

Gamma rays are emitted if a nucleus still has excess energy following radioactive decay and the emission of other particles.

57,58

Gamma rays have a high penetrating power - it takes a thick sheet of metal such as lead or concrete to reduce them significantly.

59

Physicists credit French physicist Henri Becquerel with discovering gamma radiation. In 1896, he discovered that uranium minerals could expose a photographic plate through a heavy opaque paper.

60

Gamma-rays travel to us across vast distances of the universe, only to be absorbed by the Earth's atmosphere.

61

Doctors use the gamma rays for treatment purposes, mainly for killing cancer cells, tumors and other malignant cells in the human body.

A radioactive substance, known as a tracer is put inside the human body, and its path (trace) inside the body is followed.

A special gamma camera uses those rays to build up a picture.

The patient however, gets only a small dose of the radiation and does not suffer.

62

They are also used for impurity analysis of metallurgical specimens or to determine the effects of chemicals on biological systems and plants.

Engineers make use of the gamma rays, to look for cracks in pipes and aircraft parts, since they can penetrate better than X-rays

63,64

Gamma rays can also be used for sterilizing medical products.

Umbilical Cotton tape is sterilized by Gamma radiation Sterilization.

65

http://science.hq.nasa.gov/kids/imagers/ems/uv.html

http://www.msnucleus.org/membership/slideshows/coloringbookfinal.html

http://www.msnucleus.org/membership/slideshows/light2.html