24.3 The Electromagnetic Spectrum

24.3 The Electromagnetic Spectrum

Magnetic field strength is a measure of T.

The Earth's weak magnetic field is less than a tenth of the strength of the -field.

The electric field of 1000 V/m is accompanied by a weak magnetic field.
As this wave spreads out, its field strengths become weaker.

The statement made in the module that changing electric fields create weak magnetic fields is consistent with the result of this example.

They can be detected by using the phenomenon of resonance.
A system with the same natural frequencies can be made to change.
This principle is used by radio and TV receivers to pick up weak waves and amplify them.

Draw the shape of the antenna for your TV or radio.

You can have an outdoor or indoor TV antenna if you don't have cable.

If you want to get a signal for that station, try tuning the radio to a small range of frequencies.

As the length of the antenna is changed, you should notice the quality of reception.

If you want the electron to oscillate automatically, you have to jiggle it manually.

The field can be displayed as a curve or vectors.
The electron positions are shown in the strip chart.

In this module, we look at how the waves are categorized so that we can understand some of their similarities and differences.

There are many connections with previously discussed topics such as wavelength and resonance.
Table 24.1 contains a brief overview of the production and utilization of the waves.

Water waves and earthquakes are some of the types of waves.

Propagation speed, Frequency, and wavelength are some of the shared attributes of waves.
They are always related by the expression.
There are examples of all of these characteristics for sound waves and submicroscopic particles in other modules.

An electromagnetic wave has a wavelength associated with it and travels at the speed of light.

The propagation speed of the wave, the frequency, and the wavelength are related to the relationship among these wave characteristics.

The figure shows how the various types of waves are categorized according to their wavelength and frequencies.

The characteristics of the various types of waves are related to their frequencies and wavelength.

The spectrum shows the major categories of waves.

The range of frequencies is amazing.
The line between categories is different.

There are three rules that apply to the waves in general.

High-frequency waves can carry more information than low-frequency waves.

The smaller the wavelength of the wave, the less detail it is able to resolve.

There are exceptions to the rules of thumb.

The wave can largely be transmitted if the material is transparent.

The wave can be completely reflected if the material is opaque.
The wave can be absorbed by the material, indicating that there is some interaction between the wave and the material.

It is possible to have partial transmission, reflection, and absorption.

These properties are usually associated with visible light, but they apply to all waves.
It is not obvious that something that is transparent to light is not transparent at other frequencies.
Ordinary glass is mostly opaque to ultraviolet radiation.
We can't see through people, but our skin is transparent to X-rays.

The name is applied to the waves of the same frequencies.

Radio waves from outer space do not come from alien radio stations.
Their study has shown that nature is found on the largest scales.

There are many uses for radio waves, and so the category is divided into many subcategories, including microwaves and those electromagnetic waves used for AM and FM radio, cellular telephones, and TV.

AC power transmission lines produce the lowest commonly encountered radio frequencies.

The traction power line runs to the Eutingen Railway Substation in Germany.

There is controversy about the health risks associated with exposure to these fields.

Some people think that living near transmission lines may cause diseases.
The hazard theory is not supported by demographic data.
There has been no increase in risk for cancer due to exposure to fields in recent reports.

The wavelength of radio waves affects their ability to penetrate salt water.

Since salt water is a good conductor, long wavelength radio waves are needed to reach a submarine under the surface.

Very long wavelength radio waves are needed to reach this submarine.

Shorter wavelength do not penetrate deep.

Commercial radio signals can be heard in the range of 540 to 1600 kHz.

The wave has a constant Frequency, but a varying amplitude.

A radio receiver that has the same resonance as the carrier wave can pick up the signal while rejecting other frequencies.

The receiver's circuitry is designed to mimic the original audio signal when there are variations in the carrier wave.
The audio signal is amplified to drive a speaker.

Commercial radio transmission is done in the range of 88 to108 MHz.

A carrier wave with the basic frequencies of the radio station, perhaps 105.1 MHz, is modulated by the audio signal to produce a wave of varying frequencies.

The carrier's frequencies can vary by as much as 0.020 MHz since audible frequencies range up to 20 kHz.

The carrier frequencies of two different radio stations are not close to each other.

An FM receiver has a circuitry that responds to variations in frequencies and reproduces audio information.

AM radio is more likely to be subject to noise from stray radio sources.

The reason is that waves add.

An AM receiver would interpret the noise added to its carrier wave as part of the information.

The basic carrier wave can be rejected by an FM receiver if it doesn't look for variations in frequencies.
Since noise produces a variation in amplitude, it is easier to reject it.

Each channel requires a larger range of frequencies than simple radio transmission since the waves must carry a lot of visual and audio information.

The TV audio and video signal is different.

These frequencies are for free transmission with the user using an old-fashioned roof antenna.
Satellite dishes and cable transmission of TV occur at significantly higher frequencies and are rapidly evolving with the use of high-definition or HD format.

Determine the wavelength of a 1530-kHz AM radio signal, a 105.1-MHz FM radio signal, and a 1.90- GHz cell phone signal.

The speed of light is only slightly larger in air than it is in a vacuum, so the relationship between wavelength and Frequency is where the speed of light is.

The equation can be rearranged to find the wavelength for all three frequencies.

The wavelength is related to other properties of the waves.

Some of the differences in how they are broadcast and how well they travel are accounted for by the wavelength found in the preceding example.

The most efficient length for a linear antenna is half the wavelength of the wave.
A very large antenna is needed to efficiently broadcast typical AM radio with its carrier wavelength on the order of hundreds of meters.

One benefit to these long AM wavelengths is that they can go over and around large obstacles like buildings and hills, just as ocean waves can go around large rocks.

When there is a line of sight between the broadcast antenna and receiver, radio and TV can be received.
The smaller antenna used for AM are elevated to achieve an unobstructed line of sight.

There are small structures on top of the tower that are placed at great heights to have a clear line of sight over a large broadcast area.

Astronomers and astrophysicists collect signals from outer space.
A common problem for astrophysicists is pollution from radiation from communication systems.
The facility to lock car doors remotely and be able to turn on TVs and off using remotes is one of the everyday gadgets.
In order to prevent interference between the signals, strict regulations are drawn up for different organizations to use different radio frequencies.

One reason why we are sometimes asked to switch off our mobile phones is that they use the same radio frequencies as medical equipment, which can affect their operation.

The strength of the magnetic field used and the nuclear type being scanned affects the order in which the radio waves are used.

Highly detailed two- and three-dimensional images are produced by magnetic resonance.
Radio waves are broadcast, absorbed, and reemitted in a resonance process that is sensitive to the density of nuclei.

The wavelength of 100 MHz radio waves is 3 m, yet the magnetic field strength is less than a millimeter, so details smaller than a millimeter can be imaged.

This is a good example of an exception to a rule of thumb, in that the rubric that details much smaller than the probe's wavelength cannot be detected.
There is no risk to human health from the intensity of the radio waves used.

The microwave range is from about to the highest practical resonance.

atoms and Molecules can be used to make microwaves.

The thermal motion of atoms and Molecules in any object at a temperature above absolute zero causes them to emit and absorb radiation.

microwaves are suitable for communications since they can carry more information per unit time.

Land-based long-distance transmissions are carried on microwaves.
There is a need for a clear line of sight between the transmitter and receiver.

The distance to objects can be determined by detecting and timing microwave echoes.

A shift in the radar echo can be used to determine the speed of a car.
The resolution of the radar systems used to map the Earth is limited by wavelength.

An image of Sif Mons with lava flows on Venus is based on synthetic aperture radar data combined with radar altimetry to produce a three-dimensional map of the surface.

The microwaves used to create this image were not used to create the Venusian atmosphere.

The microwaves are produced by the electrons.

An alternating electric field is created by microwaves in the oven.

Water has a negative charge at one end and a positive charge at the other.

The range of microwave frequencies is selected so that the polar molecules can absorb the electric field and increase their temperatures.

The energy absorbed results in the heating of food and not the plate, which does not have water.

There are hot spots in the food.
Food turntables help spread the hot spots.

Microwaves can be used for heating the human body.

Microwaves can penetrate deeper into tissue and achieve deep heating.
This is used to treat muscular pains.

If the power output of the oven is 1000 W, calculate the efficiency of the heat-transfer process.

A cup of water should be placed in several places along a line parallel to the opening.

Microwaves generated far away in time and space can be detected by electronic circuits.

Most of the energy in the microwave range comes from deep space, which has a 2.7 K temperature.

After detecting this radiation in 1964, Penzias and Wilson realized that it was the radiation of the Big bang's cooled remnants.

There are electronic transitions in atoms and Molecules.

The range of visible light is just below red.

Small systems, such as atoms and molecules, can vibrate fast enough to produce waves that are too high to be produced by electrons in circuits.

Water is very effective at emitting and absorbing the heat from the skin in theIR.

Night-visionscopes can detect theIR of warm objects, including humans, and convert it to visible light.

We can use a camera to look at the heat transfer from a house.

The power radiation is proportional to the fourth power of the absolute temperature and can be detected by satellites.
We preferentially warm ourselves with the help of infrared lamps, some of which are called quartz heaters, because we absorb IR better than our surroundings.

The Sun has a surface temperature of 6000 K and is a nearly perfect blackbody.

Most of the solar energy is in the visible part of the spectrum, but a small amount is in the ultraviolet.
50 percent of the solar energy is absorbed by the Earth.

The Earth's temperature is constant because of the balance between the incoming solar radiation and the Earth's radiated energy.

If there is no absorption, the greenhouse effect will cause the surface temperature of the Earth to be higher than it would be if there was.

Increased fossil fuel burning is thought to have increased global average temperatures.

The visible light is produced by the movement of atoms and the electronic transitions within them.

The atoms and Molecules are excited when they emit through electronic transitions.

This part of the spectrum is shown in Figure 24.16.

We refer to visible light as having a wavelength of between 400 and 750 nm.

Red light has the lowest frequencies and longest wavelength, while violet has the highest frequencies and shortest wavelength.

The Sun's blackbody radiation peaks in the visible part of the spectrum but is more intense in the red than in the violet.

A small part of the spectrum has visible components.

There are different divisions between visible, visible, and ultraviolet.

Plants and animals have evolved to use and respond to parts of the spectrum they are embedded in.

We enjoy the beauty of nature through visible light.
Plants are more discriminating.
The visible spectrum can be used to make sugars.

The tissue leaves should be at a temperature of.

The energy from the laser light goes to raise the temperature of the tissue and to evaporate it.

There are two amounts of heat to add together.
We need to find the mass of the tissue involved.

Concepts of thermal energy can be used to figure out how much heat is needed to raise the temperature of the tissue.

The density of the tissue and its volume are used to find the mass.

Excimer lasers are used for this eye surgery.

They can be used for precision work.
The average power rating of most lasers used for this type of eye surgery is about one watt.

The study of visible light and other forms of waves is called optical.

There are two different categories for optics.
Straight lines are used to represent the motion of the radiation when it interacts with large objects.
The study of such situations is called Ray optics.

The wave nature of the radiation can be seen when it interacts with smaller objects.

The visible light cannot detect individual atoms because they are so small than the wavelength.
All wave characteristics are included in the study of physical or wave optics.

When you light a match, you see orange light; when you light a gas stove, you see blue light.

Ultra violet is also produced by electronic transitions.

The lowest Xray frequencies overlap with the highest ultraviolet frequencies.
The solar spectrum has an invisible component beyond the violet range.

The three regions of solar UV radiation are UV-A, UV-B, and UV-C.

99% of the solar UV radiation reaching the Earth's surface is UV-A.

UV-B causes skin cancer.

As many as 20% of adults will develop skin cancer over the course of their lifetime.
If caught early, treatment can be successful.
Despite very little UV-B reaching the Earth's surface, there are substantial increases in skin-cancer rates in countries such as Australia, indicating how important it is that UV-B and UV-C continue to be absorbed by the upper atmosphere.

The aging process of the skin can be accelerated by the damage that UV radiation can cause.

sunburn is caused by large exposures and skin cancer from repeated exposure because there is so little UV-B and UV-C reaching the Earth's surface.
There is a link between overexposure to the Sun when young and melanoma later in life.

The tanning response is a defense mechanism that protects the body from future exposure to the sun.

UV-B radiation can cause damage to the DNA helix and lead to the formation of cancer cells.

Cataracts in the eyes are a cause of blindness among people living in the equatorial belt where medical treatment is limited.

Cataracts, clouding in the eye's lens and a loss of vision, are related to age and are more common in older people.
One can replace the lens of the eye with a plastic lens.
Prevention is important.
Plastic sunglasses are more effective at protecting the eyes from the sun's UV rays.

Extreme UV exposure can cause the suppression of the immune system.

Low-intensity ultraviolet is used to sterilize haircutting implements, implying that the energy associated with ultraviolet is deposited in a different way than lower-frequency waves.

The UV radiation from the flash can cause photo-degradation in the artworks, so flash photography is not allowed.

An extra-thick layer of glass in front of an artwork is designed to absorb UV radiation.

If all of the Sun's ultraviolet radiation reached the Earth's surface, there would be grave effects on the biosphere from the severe cell damage it causes.

Ozone in the upper atmosphere protects life by absorbing most of the harmful UV radiation.

Ozone concentrations are decreasing in the upper atmosphere.

An "ozone hole" in the upper atmosphere has been caused by this depletion.
The hole is larger in the spring and more centered over the southern hemisphere.
The ozone molecule breakdown is caused by chlorofluorocarbons.

The destruction of the ozone layer is caused by the release of chlorine atoms by the UV radiation.

A single chlorine atom can destroy ozone for up to two years.

Ozone depletion will be a result of the stable nature of the chlorofluorocarbons.
Air conditioning systems, foams, and aerosols have chlorofluorocarbons in them.

TheMontreal Protocol was established to phase out the production of CFC in most countries.

It is to be achieved.

India is the largest contributor to emissions.
There are signs that the protocol is working.

There is a map of ozone concentration in October of 2011.

The effect is global, as more general depletion has been observed over northern latitudes.

More damage can be caused by the Sun reaching the surface with less ozone.
Exposure to nature and use of technology are benefits of exposure to ultraviolet radiation.

A number of studies show that a lack of vitamin D can lead to the development of a range of cancers, so a certain amount of UV exposure is helpful.

Osteoporosis is linked to lack of vitamin D. Exposures of 10 minutes a day to the arms, face, and legs might suffice.
UVB gets blocked by the atmosphere in the winter time north of about latitude.

UV radiation can be used to treat some skin conditions.

It is used to kill germs in a wide range of applications.
It is used to identify substances.

Some substances, such as minerals, glow in the visible wavelength when exposed to the ultraviolet.

Posters and clothing can be seen if they are exposed to black lights.
Ultra violet is used in special microscopes to detect smaller details than visible-light microscopes.

X-rays can be created.

The electrons strike the material in the discharge current.
There are two ways in which electrons create X-rays.

An electron is accelerated in a tube.

X-rays are produced when the electron strikes a metal plate.
The electron has enough energy to ionize the atom.

An artist's conception of an electron is followed by the recapture of an electron and the emission of an X-ray.

An electron is knocked out of one of the orbits closest to the nucleus by an energetic electron.
An X-ray is created when the atom captures another electron and the energy released by its fall into a low orbit is high.

An inner-shell electron is ejected in the case shown.

A short time later, another electron is captured and falls into the space.
An X-ray is given by the energy released by this fall.
The name characteristic X-ray comes from the fact that the energy of the Xray is characteristic of the atom.

The second method by which an energetic electron creates an X-ray when it strikes a material is illustrated in The electron interacts with charges in the material The electrons and atoms in the material are transferred from the electron to the electrons and atoms.

An artist's conception of an electron being slowed by X-ray radiation.

An energetic electron is capable of hitting electrons and atoms in a material.
A second method by which X-rays are created uses an accelerated charge.

The electron's velocity can be decreased by a loss of kinetic energy.

When a charge is accelerated, it emits waves.
The waves can have high energy.
They are called X-rays.
Since the process is random, a broad spectrum of X-ray energy is emitted that is more characteristic of the electron energy than the material it encounters.
The German word for "braking radiation" is bremsstrahlung.

It was found that the discharges created a very high Frequency Electromagnetic Radiation.

There are two ways in which X-rays can be created, both of which can be caused by high-voltage discharges.

The low-frequency end of the X-ray range overlaps with the ultraviolet, but Xrays extend to much higher frequencies.

X-rays have adverse effects on living cells similar to those of ultraviolet radiation, and they have an additional liability of being more penetrating, affecting more than the surface layers of cells.

Exposure to Xrays can cause cancer and genetic defects.
X-rays can be used to treat and cure cancer because of their effect on rapidly dividing cells.

The human body and aircraft parts are opaque to visible light, which makes them the most use of X-rays.

In humans, the risk of cell damage is weighed against the benefit of the diagnostic information.
Questions have risen in recent years as to accidental overexposure of some people due to poor monitoring of radiation dose.

An X-ray image can reveal very detailed density information, because the ability of X-rays to penetrate matter depends on density.

The amount of information in a simple X-ray image is impressive, but more sophisticated techniques, such asCT scans, can reveal threedimensional information with details smaller than a millimeter.

Artificial heart valves, a pacemaker, and wires used to close the sternum are some of the interesting features shown in the shadow X-ray image.

X-rays are widely used in medical diagnostics.
Mobile X-ray units were used to diagnose soldiers during World War I.

The X-rays can be scattered to see the shape of the molecule and the structure of the crystals.

The shape of the double-helix DNA molecule was determined by X-ray diffraction.

X-rays can be used as a precise tool for trace-metal analysis in X-ray induced fluorescence, in which the energy of the X-ray emissions are related to the specific types of elements and amounts of materials present.

At least three different types of radiation were being emitted after the first detection of nuclear radioactivity in 1896.

rays are any radiation that comes from a nucleus Natural nuclear decay or nuclear processes in weapons can be the cause.

The upper end of the X-ray range and the lower end of the Frequency range overlap.

X-rays of the same Frequency have characteristics similar to Gamma rays.

They have the same uses as X-rays.

Nuclear medicine uses radiation from radioactive materials.

The figure shows a medical image.

Exposure to large amounts of radiation can obliterating responsible food spoilage organisms.
Long-term risks of consuming radiation-preserved food are unknown and controversial for some groups.
Baggage is scanned using both X-ray and technologies at airports.

This is an image of the rays emitted by nuclei in a compound that is concentrated in the bones.

Concentration in similar structures is indicative of bone cancer.
Some ribs are darker than others.

Researchers use the entire spectrum to investigate stars, space, and time.

Wilson and Penzias detected microwaves to identify the background radiation from the Big bang.

The Arecibo Radio Telescope in Puerto Rico and the Parkes Observatory in Australia were designed to detect radio waves.

The detectors of the telescopes need to be cooled by liquid nitrogen.

The signal being collected would be weaker if the detectors were not cooled.

The James Clerk Maxwell Telescope is the most famous of these telescopes.

The earliest telescopes were used to collect visible light.
Outside the atmosphere on satellites, telescopes in the ultraviolet, X-ray, and -ray regions are placed.