24 Electromagnetic Waves

• You can experiment with sunglasses.

• Slowly rotating the glasses, transformer work, and keeping the lens pointing toward the same spot.

You can achieve the same results if you look through the section titled "Explain how an electric current can be generated without a battery lens at the LCD screen of your calculator, cell phone, or laptop computer."

• You will learn in this chapter.

• Section 20.2 and 20.4 were constructed differently.

• There is a mystery.

• In this chapter, we continue to investigate that question.
• When we learn about special relativity, we'll resolve the question.

• The phenomenon that is crucial for answering the question posed in the chapter opening was neglected in our previous study of mechanical waves.

• The displacement of each section of rope at a narrow rectangular box is represented by a rope passing through the open ends of Vectors.
• Shake the rope quickly.
• The long sides of the box are parallel to them.

• The box is parallel to the shaking direction.

• The rope sections are in an original orientation.
• The rope should be shook the same way as the long sides of the box.

• The long sides of the box are facing in a different direction.

• Use two boxes.

• The rope wave parallel to the first box gets 30 from the vertical plane.
• The rope wave goes to the second box.
• In Experiment 1, shake the rope.
• Part of the box has displacements that are parallel to the box.

• If we replace the rope with a Slinky, the longitudinal displacement of the coil will always Experiments 1-2.
• They point out the direction of the wave.

• If the wave's displacement is parallel to the slit, it will not pass through.

• The wave does not pass through if the displacements are in the plane.

• When the displacements make an angle with the slit, the component of the displacements parallel to the slit passes through.

• The displacement of a longitudinal wave always goes through the box.
• The ori entation of the box does not affect longitudinal waves.

• Table 24.1 shows the effect of polarizers on boxes with proper orientation waves.

• The orientation of the wave is described by the property of waves.

• The wave is not straight.
• The particles in an unpolarized wave have this property.
• If we serve light waves in all directions in the plane, we know that the waves are not straight.

• The rope was vibrating in our experiments.
• A polarizer is a device that only contains a single part of the waves.

• In Table 24.1, the waves in Experiments 1-3 were linearly polarized.

• The wave that emerges from the No wave other side is linearly polarized.

• A wave can be completely blocked by two polarizers.

• If we can polarize light waves, they must be in the opposite direction.

• This assumption can be tested using a semiprecious crystal cal ed tourmaline, which affects light in the same way that our box affects rope waves.

• The intensity of the light is not affected by the rotation of the crystal.
• The intensity of the light is reduced to zero if you place a second crys tal to the first.

• We theorize that light is a wave of light waves and that a lightbulb emits unpolarized light waves.

• No light can pass through and only two light beams can be seen at the same time.

• The second crystal blocks the effect of two crossed components.

• There are many tiny polarizing crystals embedded in a sheet of material.

• There is a film with polarizers.
• There are physics teaching labs that have polar remove all of the light.

• There is no light coming through the overlap region of the crossed polarizers.
• This behavior is similar to the behavior of mechani cal waves passing through mechanical polarizers that support the hypothesis of light waves.

• A light meter is placed a fixed distance from a lightbulb.

• A polarizer is placed between the bulb and the detector.

• There are two polarizers between the bulb and the detector.

• Depending on the angle between the polarizers, the second polarizer seems to further reduce the intensity.
• The relation between this reduction and angle needs to be deterred.

• The intensity of light passing through the second polarizer decreases as the angle between the axes of the first and second polarizer increases.
• It cannot be a function that is constant.

• Maybe it involves the function.
• The cos 30 is more than the 0.75 for 30 in the second row.
• The second polarizer oriented at 30 causes a decrease in the intensity of light.
• The angle between the axes of the two polarizers is known as cos2u.
• After leaving the first and second filters, 0>2 is the light inten sity.

• The intensity of the light by cos2u is reduced by the polarizer.

• In Table 24.1, we found that the effects of polarization can only be seen with the waves that are longitudinal.

• We need to look at how a wave travels through a medium to answer this question.
• Think about what happens when a wave travels through a Slinky.
• When one coil is displaced, the next coil is pulled in a different direction.
• The coil next to it does the same thing.
• The elastic forces point to the wave's propagation direction and speed the displaced coils back to equilibrium.

• There are two hypotheses here.

• Light travels through an elastic me dium.
• The medium is transparent and has no mass.

• A light wave is a new type of vibration that does not involve physical particles vibrating around equilibrium positions due to restoring forces being exerted on them.

• The second hypothesis was tested by the studies of electricity and magnetism.

• Before the second half of the 19th century, the investigations of light and elec tromagnetic phenomena proceeded independently.

• A constant electric field is produced by stationary electric charges.

• There aren't any magnetic charges.

• An electric field is created by a changing magnetic field.

• The consequences of Maxwell's equations were important.
• No electric charges or currents are present in this feedback loop.

• The propagation of fields can be done without charges or currents.

• We talked about vacuum permeability in the chapter on mag netism.

• The speed of light in air had been measured and was in line with the value.
• This was the second testable consequence of Max well's model.

• The hy pothesis was the first to be tested by a physicist.

• A large electric field can be seen between the dark room former and the primary coil of a trans after hours.
• The potential difference field would produce an electric wave if he was correct.

• When the wave reaches the receiver loop, it sparks between the differences across the secondary coil, which in turn would cause a current in the loop and cause a receiver to charge the spheres.

• The receiver was separated by a small gap and connected to a loop of wire.

• Something had traveled from the transmitter to the receiver when the hertz showed the spark between the spheres of the receiver.

• The first evidence for the existence of waves was provided by the experiment conducted by Hertz.
• In order to find out if the waves generated in his experiment had the same properties as light waves, he did many more experiments.
• He found that Hertz's waves had a lot of smal er frequencies than the light waves we are familiar with.
• He used metal sheets of different shapes.
• They were allowed to pass through different media.
• He observed interference after performing an analogue of a double-slit experiment.

• He used a metal fence to observe the waves.
• He performed experiments to measure the propagation speed of the waves.
• The idea that light could be modeled as a wave of electric and mag netic fields was supported by these experiments.

• The direction of travel of the wave causes each field to vibrate.
• There is a new model of light that travels in a vacuum and in other media.
• The speed of light in a vacuum is not known.

• The first transmission of information via radio waves, one form of electromagnetic waves, took place in 1892.
• The English Channel had successful radio wave-based communication by 1899.

• Cell phones, two-way radios, and over-the-air radio and television use them.
• The alternating emf leads to the charging and discharging of the two ends of the antenna.

• alternating current is produced by the source of alternating emf.

• The elements the current is downward after the power supply is turned on.
• The bottom of the emf source becomes positively charged and the top becomes negatively charged after a very short time interval.
• The current reverses direction when the antenna is connected to a source of alternating emf.

• The process continues in the opposite direction, repeating bil lions of times each second.

• The fields shown in (a) correspond to the second part in (e).
• The fields in (b) correspond to the third part in (e).

• There is a noticeable difference between the two situations.

• The electric and magnetic fields are produced by an antenna.

• The pattern looks like a simple one.

• The out-of-phase contri bution is less significant farther from the antenna than it is from the in-phase contribution.
• Maxwel's in-phase waves are significant far from the antenna.

• The shape and size of the antennas are selected so that they can send and receive waves with a specific wavelength range.

• The wavelength of the electric field in the metal antenna is different from the wavelength of the EM wave in the air, but they are related.
• The wavelength of the EM waves passing through them is affected by the re fraction of different materials.

• Knowing the index of refraction of the antenna material allows us to choose an antenna length that will efficiently produce waves of the desired wavelength.
• The wavelength is one-third of its value in the air.
• The length of the phone antenna needs to be in line with the size of the phone.

• We can review how our understanding of light has changed over the past four chapters.
• We learned about shadows and reflections.
• We used a particle model to explain that light consisted of tiny particles that travel through a medium.
• The nature of these particles was not specified by the model.
• The particle model could not explain what happens when light passes through narrow openings.
• We went to a wave model.
• The idea that a light wave is a wave came from observations of the light's polarization.
• The electric and magnetic fields are vibrating in a light wave, which is proposed by the electromag netic wave model of light.
• Examples of practical applications of the new model of light are given in the next section.

• When a police officer uses radar to catch speeding motorists, we use the same type of waves that are present when we listen to the car radio or use a gps system.

• Speech, music, and video can be transmitted over long distances using these and even higher frequencies.
• Radar is a practical application of radio waves.
• Radar devices help locate airplanes, determine distances to planets and other objects in the solar system, and find schools of fish in the ocean.

• The receiver is connected to a sophisticated type of amme ter that can measure the current produced when a reflected wave arrives.
• The emitting antenna and the receiving antenna are the same antenna.

• A radar system is being used to detect aircraft.
• The time in terval shows the distance to the aircraft.
• The farther away the aircraft is, the longer it takes the pulse to return.

• It isn't as effective in tracking objects that can detect an airplane.

• After the second pulse has left, the reflected pulse returns if the object is so far away.

• Tracking objects that are flying close to the ground is one of the limitations.
• The person standing on the ground can see 5 km from the horizon.
• The ground will block the line of sight for a target that is more than 5 km away.
• The radar system needs to be mounted on a tal tower in order to increase the horizon distance.

• The range of distances is the target from the radar.

• The maximum range from the radar is determined by the period.

• A target outside the range of 1.6 km to 20 km will not reflect off other objects.
• The radar system can detect the radio wave pulse.
• Military radars travel in a vacuum and can detect ob slower than civilian radars.

• Global positioning systems allow us to determine our location using elec- circle Earth as part of the Global positioning tromagnetic waves and a system of satellites.
• Three or four satellites triangulate to determine your location.

• The U.S. Air Force operates the Navstar Global Positioning System.
• Navstar has three main components.

• The signals from multiple satel ites are detected by the receiver.

• The control system maintains accurate information about the satel ites.

• The receiver uses signals from at least three satellites to determine your position on the ground.
• The re ceiver can determine your altitude with signals from four or more satel ites.
• The clock in your unit is synchronized to the clock on the satel ites within a tenth of a second.
• At the same time each satellite sends a microwave signal, your gps starts a measurement.
• The time of arrival of the signals from the satel ites is measured by your unit.

• The surface trilateration is similar to the gps.

• A visitor from overseas is unsure of his location while in the United States.
• There is a sign that says Atlanta, Minneapolis, and Philadelphia.
• The visitor has a map of the United States and draws a circle around it.

• There is only one place where the three circles intersect.

• In the same way, your gps system locates your current position.

• The unit constructs spheres around each of them with corresponding radii.
• Your location is where the spheres intersect.
• The accuracy of the handheld units is 3 to 10 m.

• Indianapolis is the farthest away from the other three cities.

• Spencer accidentally discovered microwave cooking in 1945.
• Spencer felt a candy bar in his pocket melt as he stood in front of one of the tubes.

• The popcorn popped when he put it in front of the tube.

• He put a raw egg in front of the tube.

• To understand what's happening, we have to think about tiny things.

• The positively and negatively charged regions of the molecule are affected by the electric field of the microwave.
• The water molecule flips over billions of times a second.

• Molecules that are not electric dipoles.
• The internal energy of the food is transformed into the electric and magnetic energy in the microwaves.

• Light waves of different frequencies travel at different speeds in nonvacuum media such as glass or water.

• Maxwel's equations show that the waves can have any frequencies.
• AM radio stations emit low frequencies.
• The highest frequencies of Cosmic Ray EM waves have ever been detected.

• The broadcast band on the radio is from 88 to108 MHz.

• The radio wavelength is between 2.8 m to 3.4 m.

• The AM radio stations broadcast in the wave dex of air are very close to the vacuum length range of 556 m to 186 m.

• Our ears can only hear sounds between 20 and 20,000hertz, which is less than the frequencies of satellite radio stations.

• The information that gets converted into the sounds we hear is converted into tiny variations in the carrier wave.

• The receiver decodes the variations and converts them into an electric signal that a speaker can use.

• In that case, the carrier wave's amplitude is varied rather than its frequencies.

• A narrow range of the spectrum is what visible light illuminates.

• We have already encountered radio waves and microwaves.
• In Chapter 12 we encountered another type of radiation.
• Scientists thought that visible light and thermal radiation were different.
• They thought that the light that came from a fire in a fireplace was different from the warmth that came from it.
• We now know that they are both waves with different frequencies.

• We discuss the production of radiation in later chapters.

• Table 24.4 shouldn't be read too literally.
• Most objects emit different amounts of these types of waves.
• Cold gas clouds in our galaxy mostly emit radio waves but also emit a small amount of visible light.
• Stars similar to our Sun emit a lot of visible, visible, and UV, but also produce some radio waves and X-rays.
• Your body emits all types of EM waves, with the exception of UV and X-ray.

• The speed of waves in the vacuum is108 m>s.

• The above equation can be checked with unit analysis.

• The units for magnetic field are T 1tesla2 and 1newton.

• The mathematical descriptions of waves are used as a guide.

• The concept of electric field energy density can be expressed through the idea of a system of electri cally charged objects.

• The answer is yes, but we won't develop the ideas needed to establish this.
• The energy in an EM wave is carried by the electric and magnetic fields.

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• We arrived at Eq.

• We won't go through the details, but here's the result: the average value of the square of a sinusoidal function is half the maximum value.

• It might appear dim to you if you look at a source of light.
• It could be like a car with its high beams on.
• The average energy density is the speed of light.

• Remember that intensity is the amount of energy that passes through a unit area during a time interval.

• The rate of the wave is intensity.
• The average intensity is determined by the wave's average energy crossing a surface.

• Imagine wind blow ing into a sail as a way to think of intensity and energy density.

• We will be determining the sity of the Sun's radiation when it arrives on Earth.

• We know that.

• The Eq is being used.

• 103 W>m22 is normal to the surface.

• The bulb produces a surface that is less than 1 m2 from the Sun's rays.

• Try it yourself.

• The bulb emits energy in the form of waves.

• The Earth's atmosphere is poor.

• There is a more powerful model of light.
• This model can be used to understand how light is produced, how sunglasses work, how to reduce glare from sunlight, and the role of polarization in liquid crystal displays on computer and calculator screens.

• The mechanism behind this phenomenon is discussed in this section.
• We first look at the production of light by an antenna.

• The radio waves are produced by 909 electrons vibrating up and down in an antenna.
• The antenna is parallel to the po-.

• The light produced by the bulb is unpolarized.

• The waves are produced by independent atomic oscillators.

• Most of the time, the protons and electrons that make up mat ter don't have any sort of motion, so the electric field has a much more significant effect on matter.

• The dimensions are much smaller than for light.

• The chains are stretched in one direction.

• The wires are parallel to the grill.

• The axis of the light polarizer is related to the direction of the stretched polymer chains.

• The par viewed through a polarizer with its axis oriented parallel to the allel component is not as bright as the reflected light intensity.
• When viewed with the polarizer parallel to the reflecting surface, the reflected light becomes very dim.

• The beam is completely blocked by the "perpendicular" polarizer.

• The 90 angle with the reflected ray is the same as the polarizing angle up.

• The experiments show the tan up of the polarizing angle up.
• The polarizing angle is not the same as the other one.
• The water has a refracted Refractive index.

• Light reflected off the boundary between two transparent media becomes partially linear.

• The reflected light and the refracted light make a 90 angle relative to each other for light incident at the polarizing angle.

• Snel's law helps us understand.

• The figure is in Table 24.5.

• We know that sin190 - up2 is cos up.

• The law Light is traveling in medium 1 when it reflects off medium 2.

• The law explains how polarizing sunglasses help reduce glare.

• It is difficult to see when driving toward the Sun because of the reflected light from the hood and dashboard of other cars.
• The light is reflected to the surfaces.

• The glare is reduced by absorbing light in that direction.

• We sketched the situation.

• The water surface is horizontal and parallel to the ocean.
• The page should be at what angle above the horizon.

• The law states that the angle at which paral el rays from the Sun completely paral el to the water surface should produce reflected light is called the larization angle.

• The tical normal line has a polarizing axis.
• The direction of the sunlight above the horizontal is shown in the picture below.
• The water reflects the rays from the Sun as if it were a mirror.

• The reflected light will page for other incidents.
• If the polarizing axis of the glasses is not aligned with the sunglasses, the reflected light will not pass though the glasses.

• When the Sun is very low or without a film, the sunglasses are not effective.

• Most of the time we are looking at objects that are not very far away, such as a car a few hundred feet ahead or water near the horizon.
• When the sun is close to the horizon, the light reflects toward our eyes at larger angles that result in the light not being strong.

• The light reflected from the top part of the car doesn't cause a lot of glare.
• The light reflected from the car is seen by the bottom half of the rearview mirror.

• The sky appears blue because the atmosphere scatters blue light more than red into your eyes.
• The intensity of the light passing through the glasses can change if you look through them at the clear sky.
• Light scattered by the atmosphere is partially reflected.
• The sky is almost dark because of the scattered light.
• The sunlight appeared to be scattered toward you.

• We need to assume that the molecule in the at mosphere are like the tiny dipole antennas described at the beginning of this section.

• The light strikes a molecule consisting of particles carrying opposite charges and they vibrate as the wave passes.

• Light from a clear with a vibrating electric charge cannot emit a sky of 90.

• Light from clouds is unpolarized.
• Light entering a cloud is randomly scat tered by water droplets before it leaves.

• The polarizers move downward.

• Liquid crystals have both solid and liquid properties.
• They can flow like a liquid, but they are oriented in an orderly manner.
• The operation of the screens is affected by polarization.

• Consider a calculator display.
• Some parts of the display are bright and some are dark.

• The axes of the panels are parallel to each other.
• Light from behind the clear sky but not from the clouds is affected by a polarizer.

• The screen is bright.

• Light escapes from liquid crystals.

• The light gets through the door.

• The screen looks dark because light doesn't pass through the second panel.
• In this case, the pixel is gray.

• You can see the patterns on the calculator screen.

• One way of making a viewable 3D movie is through polarization.

• There are two images on the screen.
• The two images have axes that are 90 degrees from each other.
• The two images reflect from the screen to the audience.
• Each eye sees a different image.
• You can see the 3D effect in the same way you see the real world without the help of 3D glasses by combining the two images in the brain.

• There is a different image on the surface of a car.

• The magnetic field can be produced by the electric field changing.

• A changing electric field produces a magnetic field waves when it is stationary.
• The electric field lines produced by static electric charges arelocity.

• Magnetic field lines are closed.

• The object will double if it is attracted to the north.

• The light reflected off the lake is not polar.

• The following depends on the polarizer through which you observe it.

• A pair of glasses are marketed as having po 13.
• Light phenomena can be better explained by larizing filters.

• The evidence supports the wave 28.

• Jim doesn't understand the wave model of light.

• Explain to Maxwel that light can travel in a vacuum way to show each of his equations.

• Make a list of 21 phenomena.
• The wave model of light can be used to explain the distances of objects.

• There is a difference between the two statements.

• If you want to derive a specific answer, place two smal electrical y charged objects at a distance.

• The electric field is difficult due to these two objects.

• A straight wire has a current of 0.20 A.

• There are marked poles to draw a bar magnet.
• The tude of vibrations is 20 cm.

• A 40-W lightbulb is close to a screen.
• What is the intensity?

• The area of the loop is 10 m2.

• There is a crystal in front of the screen.
• There is an electric field.

• You should investigate in detail how the apparatus worked.
• Explain how the properties of the spar contributed to the understanding of light as a wave.

• You can design an experiment to find out if 12 is true.
• If you want to observe reflection sound, describe the experiments that you did.
• Discuss how the outcome would affect the waves.

• The pulse width is what characterizes the radar.
• There is an increase in brightness of a star.
• The radar can measure.

• The speed of light in water objects is 1.33 times less than in the air.

• You can support your answer with a sketch.
• You need to raise the radar on an AM radio station.

• A wave- 25 is used for radar.

• The wave is 500 m in length and has a radius of 6000 km.

• The 20 are affected by UV-A rays.
• There is a star in the sky.

• UV-B rays can cause cancer.
• The wave is 100,000 light-years in diameter and has a light length range of UV-A to 400 nm and a light travel time of one year.

• Each second, the Sun emits about 1026 J of radiation.
• The distance from Earth to the Sun is about 1011 m.

• About 10% of the energy from the bulb is visible light.
• The bulb emits most of it's energy in the middle of the spectrum.

• Explain how the information about energy is distributed.
• The direction the spider is moving is indicated by the pose.
• The use of this information is required after the problem has been solved.

• If the spider orients its head so that one of the fields is close to the Sun, that would be great.
• List the light intensity 800 W/m2 and the tions that you made.

• The sheets are oriented at an angle of 60 degrees.
• A 1.2 J unpolarized light beam is reduced after passing through energy during a 27 - 15@s time interval at a wavelength both sheets.

• The light reflected from a smooth pond wave is described in the equations below.

• Tell everything you can about 45.
• The light goes through three polarizers.
• The equations describe the wave.

• There are two pairs of glasses.
• Make a list of questions you can answer with one of them.

• A color filter is a transparent material that you need to know if you want to answer the light of a certain color or not.

• You can perform an experiment to determine if the star exploded as a supernova.
• Late-stage stars whether the light from a particular source is unpolarized or ejected material that forms a ring before it explodes.
• How can you determine vas if the latter is the case?
• The ring is not visible.

• The second sheet should be light to estimate the distance to the supernova.

• The survival of a bee colony depends on the ability of bee scouts to locate food.
• After finding a promising food source, a honeybee scout returns to the hive and uses a waggle dance to tel its worker sisters the direction and distance to the food.

• Light from the Sun is unpolarized.

• The direction of the Sun is used by bees as a reference.
• The direction toward the Sun is represented by the upward direction in the hive.
• The middle line of the scout's waggle dance resembles a figure eight that indicates the direction of the food relative to the direction of the Sun.
• A rod in the eye's the right of the hive indicates a food source that can see light.
• To the right of the direction toward the Sun, estimate the side that is 50deg.
• The rod can detect the light's dis power.
• Depending on the time the scout takes, indicate the amount of food you want to serve.
• You need more information than MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE MzE

• Even if the Sun is 50, the other bees know where to go.
• They can detect the degree of polarization in other open the transmission of AM stations but not affect the position of the Sun in the sky.
• Radio stations don't broadcast in remote areas.
• They learned from the scout the angle from the Sun's direction to possible reasons for these phenomena.

• Light from the source went through an interrupter and M reflected from the mirror.

• If the light hit the tooth of the 1 s wheel, Fizeau wouldn't see it.
• The time interval between teeth crossing the beam and the distance light traveled could be used to measure the speed of light.

• The width of one tooth was equal to the number of teeth in the wheel.
• The bees know the direction to the Sun.
• Direct sunlight is linearly polarized using these parameters.

• The formula for calculating the speed of light was created by Fizeau.

• The bees have never been to the food source when they head toward a region of the sky with a flowery odor.

• There is partially unpolarized light coming from it.

• In Fizeau's experiment.
• If the direction of the middle line of the scout's waggle dance was to the left of the upward direction, the wheel made 29 teeth and the mirror made 53 teeth.

• Each year in the United States, the Department of Energy uses about 8 * 1017 J of elec (c) for household Sun's direction lighting.
• Where the light is 80% linearly polarized to the left of the diode bulbs use about one-fourth of the energy of incandes Sun's direction cent bulbs.
• The need for power produced by the Sun's direction coal-burning electric power plants would be reduced if the light is 100% linearly polarized to the left of the house.

• The strontium vibrates in all directions.
• The United States and other countries are not allowing the travel of the dicular in the direction of the sun.

• The answer is close to the rate of visible light emis Sun.

• In 2009, Australia, Canada, New Zealand, and the European Union phased out incan lightbulbs.
• Phase 62 is for the United States.
• You could change all of the lightbulbs to make them out of date.
• The world's energy-efficient bulbs used one-fourth of the amount of energy for 90 years.

• The particles emit a sound.
• How much money will you save on your electric bill each year?
• If you replace five 100 watt incandescent bulbs with five 100 watt fluorescent bulbs in your skin and on the Sun, you'll get the same effect.
• A person's skin emits most of its radiation in the low-frequency, long-wavelength sume that the bulbs are on and that electric energy is called thermal radiation.