Electromagnetic Waves – The Physics Hypertextbook (2022)

Discussion

maxwell's equations

Warning: big, fancy calculus derivation approaching. If you don't like or don't understand vector calculus, just skim through everything down to the paragraph before the last equation. The descriptive text is fairly easy to read.

Start with Maxwell's equations in derivative form for empty space.

∇·E=0(Gauss)
∇·B=0(noname)
∇×E=B(Faraday)
t
∇×B=μ0ε0E(Ampère)
t

These equations are first order, which usually means the mathematics should be easy (good!), but they're also coupled, which means it might be difficult (rats!). Let's separate them using this little trick. Take the curl of both sides of Faraday's and Ampère's laws. The left side of each equation is the curl of the curl, for which there is a special identity. The right side of each equation, on the other hand, is the curl of a time derivative. We'll switch it around into a time derivative of the curl.

∇×E=B
t
∇×(∇×E)=∇×

B

t
∇(∇·E)−∇2E=(∇×B)
t
∇×B=μ0ε0E
t
∇×(∇×B)=∇×

μ0ε0E

t
∇(∇·B)−∇2B=μ0ε0(∇×E)
t

Now if you look carefully, you'll see that one term in each equation equals zero and the other can be replaced with a time derivative.

0−∇2E=−

μ0ε0E

tt
0−∇2B0ε0

B

tt

Let's clean it up a bit and see what we get.

2E0ε02E
t2
2B0ε02B
t2

These equations are now decoupled (E and B have their own private equations), which certainly simplifies things, but in the process we've changed them from first to second order (notice all the squares). I know I said earlier that lower order implies easier to work with, but these second order equations aren't as difficult as they look. Raising the order has not made things more complicated, it's made things more interesting.

Here's one set of possible solutions.

E(x,t)=E0sin[2π(ftx+φ)]
λ
B(x,t)=B0sin[2π(ftx+φ)]
λ

This particular example is one dimensional, but there are two dimensional solutions as well — many of them. The interesting ones have electric and magnetic fields that change in time. These changes then propagate away at a finite speed. Such a solution is an electromagnetic wave.

Let's examine our possible solution in more detail. Find the second space and time derivatives of the electric field…

2E=−2E0sin[2π(ftx+φ)]
λ2λ
2E=−4π2f2E0sin[2π(ftx+φ)]
t2λ

and substitute them back into the second order partial differential equation.

2E0ε02E
t2

Work on the left side first.

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2E=−2E0sin[2π(ftx+φ)]
λ2λ

Work on the right side second.

μ0ε02E0ε0{−4π2f2E0sin[2π(ftx+φ)]}
t2λ

Set these two experssions equal to one another and watch. All kinds of stuff cancels.

10ε0f2
λ2

Rearrange a bit.

(fλ)2=1
μ0ε0

I see a wave speed in there (c=fλ). We'll use c for this one since it's the first letter in the Latin word for swiftness — celeritas.

c=1
√μ0ε0

Very interesting.

Given Maxwell's four equations (which are based on observation) we have shown that electromagnetic waves must exist as a consequence. They can have any amplitude E0 (with B0 depending on E0 as will be shown later), any wavelength λ, and be retarded or advanced by any phase φ, but they can only travel through empty space at one wave speed c.

c=1
√μ0ε0
c=1
√[(4π×10−7Tm/A)(8.8541878128×10−12C2/Nm2)]
c=299,792,458m/s

In the words of Maxwell…

This velocity is so nearly that of light, that it seems we have strong reasons to conclude that light itself (including radiant heat, and other radiations if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws.

James Clerk Maxwell, 1865

This is the speed of light in a vacuum, which means that…

  1. Electromagnetic waves propagate at the speed of light.
  2. Light is an electromagnetic wave.
  3. There are other forms of electromagnetic radiation.

Those are the three important conclusions from this mathematical excursion.



history

Let's recall the steps that led to the formulation of Maxwell's four laws.

  1. Gauss's law is an extension of Coulomb's law and has its origins in the study of charged objects and the forces of attraction and repulsion between them. In everyday terms, the study of static cling, which has its roots in ancient times when it was noticed that amber rubbed with animal fur attracted bits of cloth and paper. The Greek word for amber, ηλεκτρον (elektron), is the root of the English words electric, electrical, electricity, electrician, and so on.
  2. No one's law comes from the observational fact that every magnet has both a north and a south pole. No one has ever seen a magnetic monopole. Whenever a magnet is broken it always has a north and a south pole. This is true down to the subatomic level. From this observation we can deduce that magnetic field lines must form continuous loops. The study of magnetism goes back to the time when magnetic rocks were first found by peoples around the world — most notably outside the ancient Greek city of Magnesia, which is the root of the English word magnetism.
  3. Faraday's law deals with induced electric currents. Given a loop of wire and a magnet, one can induce current to flow through the loop by moving the loop or moving the magnet. The static charges studied by Gauss, Coulomb, and Franklin can be made to move by the unusual rocks found lying around in the lands of the old Greek Empire.
  4. Ampère's law originally dealt with the magnetism that arose from moving charges. Run charges through a wire and you've made a magnet — an electromagnet. Maxwell's key insight was that the space between two parallel metal plates in the process of being charged will behave in a manner similar to the space around a current-carrying wire. There's the magnetism that comes from electric currents (like the current through a working electromagnet) and the magnetism that comes from displacement currents (like the changing electric field in a capacitor that's just been switched on or off).

It is the last law in the list — Ampère's law as modified by Maxwell — that is the key. A changing electric field can produce a magnetic field in much the same way as an electric current can produce a magnetic field. Thus, electric charges did not have to flow or even to exist. A changing electric field will generate a changing magnetic field all on its own. This would result in a changing electric field, which would result in a a changing magnetic field, and so on — the whole thing flying away out into empty space at the speed of light.

The implications are huge. Perhaps there are other forms of electromagnetic waves that are invisible to the human eye. The equations impose no limits on wavelength or frequency. The only requirement is that they propagate with the speed of light in a vacuum.

These conclusions were made in 1864 before there was any experimental evidence for invisible electromagnetic waves. Before Maxwell there was light and nothing else. Now we have an unlimited electromagnetic spectrum that includes radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays. Perhaps the most amazing thing about this story is not that Maxwell showed that light was an electromagnetic wave, but that he stumbled upon it. It wasn't his goal. It was an unintended consequence. To quote Maxwell once again…

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The value of [c] was determined by measuring the electromotive force with which a condenser of known capacity was charged, and then discharging the condenser through a galvanometer, so as to measure the quantity of electricity in it in electromagnetic measure. The only use made of light in the experiment was to see the instruments. The value of [c] found by M. Foucault was obtained by determining the angle through which a revolving mirror is turned, while the light reflected from it went and returned along a measured course. No use whatever was made of electricity or magnetism.

The agreement of the results seem to show that light and magnetism are affections of the same substance, and that light is an electromagnetic disturbance propagated through the field according to electromagnetic laws. [expand]

Amber, animal fur, rocks from Magnesia, loops of wire, and batteries connected to metal plates. What else have I missed? Dutch gentlemen wrapping glass jars with metal foil and shocking each other; Franklin flying a kite on a stormy, summer afternoon; and Chinese sailors navigating with compasses. You might not see it today, and you definitely wouldn't have seen it coming in the middle of the 19th century, but these seemingly disconnected events are all related by the speed of light. This means we must add to the list Newton, Snell, Fermat and all the rest watching light bend through glass; Young's double slit apparatus; and Galileo with his telescope to name but a few. Although none of them knew it at the time, they were all working on the same vast project — the study of electromagnetism.

The rest is history…

  1. James Clerk Maxwell (1831–1879) Scotland–England
    Prediction of electromagnetic waves
  2. Heinrich Hertz (1857–1894) Germany
    Experimental confirmation of radio waves (spark gap transmitter-receiver)
  3. Guglielmo Marconi (1874–1937) Italy
    First transatlantic Morse code transmission (England to Newfoundland)
  4. Reginald Fessenden (1866–1932) Canada–Bermuda
    First amplitude modulation broadcast (AM)
  5. Philo T. Farnsworth (1906–1971) USA
    First all-electronic television broadcast
  6. Edwin Howard Armstrong (1890–1954) USA
    First frequency modulation broadcast (FM)

energy, power, and pressure

The electric field describes an electromagnetic wave completely in free space. The magnetic field is related to the electric field by a simple relationship. Start from Faraday's law.

∇×E=−B
t

Work on the left side first. Substitute the one dimensional wave equation for electricity and find its curl.

∇×E=∇×{E0sin[2π(ftx+φ)]ĵ}
λ
∇×E=E0cos[2π(ftx+φ)]
λλ

Work on the right side second. Substitute the one dimensional wave equation for magnetism and find its time derivative.

B=−{B0sin[2π(ftx+φ)]}
ttλ
B=−fB0cos[2π(ftx+φ)]
tλ

Set the two sides equal. Cancel the cosine terms and some other stuff.

1E0=fB0
λ

Rearrange it to look nice…

E0=fλ
B0

and then recall that fλ is the speed of light.

E0=c
B0

Well, we actually cancelled out too much stuff. This relationship holds true for all field values, not just the maximum. The ratio of the electric to magnetic fields in an electromagnetic wave in free space is always equal to the speed of light.

E=c
B

This knowledge can then be used to simplify the energy density situation a bit. Start with the magnetic energy density and replace it with an expression containing the electric field.

ηB=1B2=1

E2

00c2

Recall that the speed of light is related to the permeability and permittivity constants.

c=1
√μ0ε0

So…

10ε0
c2

And thus…

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ηB=1μ0ε0E2=ε0E2
02

Look familiar? It's the electric energy density. For an electromagnetic wave in free space, half the energy is in the electric field and half is in the magnetic field

η=ηE+ηB
η=ε0E2+ε0E2
22

This gives us this compact equation for the total energy density of an electromagnetic wave…

η=ε0E2

or this one, if you prefer to state things in terms of the magnetic field instead…

η=1B2
μ0

This is an interesting and simple set of relations, but keep in mind that it only works for electromagnetic waves in free space. Things are different in a media and the electric and magnetic fields can have any values they want if they're static (meaning there's no accelerating charges).

Since waves are spread out in space and time, energy density is often a more useful concept than energy. By extension, the power of a wave should probably be replaced with the more useful concept of its power density. Since the energy content of a wave fills a volume of space it makes sense to define energy density as energy per volume.

η=U
V

Since power is energy on the move, the notion of power existing in a place doesn't make much sense. Instead we should speak of the power delivered to a place. The boundary between one place and another is described by an area. What's the difference between being inside a room and outside the room? The answer is what side of the doorway you're on. How is this opening described? By its area. The sensible definition of power density is then power per area.

S=P
A

This quantity is also known as irradiance, radiant flux, emissive power, energy flux or energy flux density. None of these words begin with "s" so why S was chosen as the symbol is unknown to me. Since I've also seen this quantity represented by the symbols q, j, and E maybe what I really should be saying here is I don't know why I chose S. My guess is that it's the way I learned it way back when and therefore it's the way you should learn it too.

The unit of this quantity is the watt per square meter, which has no special name.



W=W

m2m2

We'll start the analysis of this quantity by recalling the definitions of power (the rate at which energy is transformed) and energy density (energy per volume).

S=P=1U=1ηV
AAtAt

Now, imagine a beam of light or radio waves or any other kind of electromagnetic wave landing on a surface. The energy that falls on this surface in a given amount of time fills a column that travels through space at the speed of light. The volume of this column is the area of its base times its length. The area can be any arbitrary size, since we're dealing with a density here, and the length of this column is determined by the time it takes for the column to land on the surface while traveling at the speed of light. Let me show you what I'm talking about with mathematical symbols.

S=ηV=η(Aℓ)=η(Act)c
AtAtAt

The next steps involve replacing η and c with the special relationships discussed earlier.

Sc=

1B2

E
μ0B

And here's what we end up with…

S=1EB
μ0

Certainly not what I expected, but this is the traditional way to write the power density of an electromagnetic wave. Well… almost. The real equation is written in vector form like this…

S=1E×B
μ0

and is given the oddly appropriate name poynting vector, not because someone was making a joke about how vectors "poynt" but in honor of its discoverer, the English physicist John Poynting (1852–1914). Poynting's derivation involves vector mathematics that isn't appropriate for the level of this book. (Translation: I don't understand it.)

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The poynting vector is important because it aligns the three vectors of an electromagnetic wave: the electric field, the magnetic field, and the direction of propagation. These three vectors are mutually perpendicular; that is, each is perpendicular to the other two. Their relative arrangement is determined by the right hand rule of the cross product (that is; the × between E and B in the equation).

The example shown in the diagram below is consistent with this rule. Check it out for yourself. Mentally pick a pair of vectors coming out of the same point on the wave. Hold your right hand flat in front of your face with your thumb stuck out on the side at a right angle in the shape of an "L". Now rotate your hand until your fingers point in the direction of the electric field and your palm faces in the direction of the magnetic field. If your hand is aligned properly you should be able to fold your fingers so they point in the direction of the magnetic field. (Don't move your thumb.) This action imitates the "crossing" of the electric field into the magnetic field. The direction of this cross product is the poynting vector and is indicated by your thumb. If you've done this activity correctly, your thumb should be point out of the screen toward your face. The orientation of the rest of your hand depends on whether you aligned you fingers with an electric field vector pointing left or right. One of them is easy on the hand and the other makes you look like you're performing some odd form of yoga.

As we learned in an earlier section of this book, waves transfer both energy and momentum without transferring any mass. That might seem obvious for mechanical waves (especially if you've ever been bowled over by a strong ocean wave) but when's the last time you ever felt pressed by a radio wave or knocked down by a beam of light? We just don't experience radiation pressure. Still, it is something we can compute.

Begin with the definitions of pressure (force per area) and work (force times distance) and see what happens.

P=F=F=U
AAV

Well that's interesting. Pressure and energy density are the same thing. The only problem is that with waves there is no single value for the energy density. It's a quantity that fluctuates in time and space. What we really need here are time-averaged values. Such quantities are represented by the symbol between two angle brackets. Like this…

P=F=F=U=⟨η⟩
AAV

That's how you write it and here's how you do it for the case of a simple sine wave. Integrate the energy density equation over one period.

P=⟨η⟩
P=1

ε0E2dt
T
P=1

ε0

E0sin2π

ftx⎞⎤2
⎟⎥
⎠⎦
dt
Tλ
T



0
P=ε0E02

sin2π

ftx⎞⎤2
⎟⎥
⎠⎦
dt
Tλ

That may look like a big mean integral, but it's not. Think of what the sine squared curve looks like. It's a wiggly line that goes up and down between 0 and 1. Over one complete cycle it splits a box 1 high by T wide in half. This gives us…

P=ε0E02T=½ε0E0
T2

which you might recognize as half the energy density.

P=½η

The radiation pressure of an electromagnetic wave isn't equal to its energy density, it's equal to half its energy density. I believe this mathematics, but I think I still need to prove to myself that this equation is real. As I noted earlier, I've never felt pressed by a radio wave or been knocked down by a beam of light. It must be an exceptioanlly weak effect. We'll confirm this through computation in the practice problems that accompany this discussion.

miscellaneous

Do I need to discuss the impedance of free space here?

Z=√μ00c
ε0

Show that this has ohm as the unit

Compute it.

Z0c
Z=(4π×10−7Vs/Am)(299,792,458m/s)
Z=376.730…Ω

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FAQs

What does electromagnetic waves mean in physics? ›

Definition of electromagnetic wave

: one of the waves that are propagated by simultaneous periodic variations of electric and magnetic field intensity and that include radio waves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

What are electromagnetic waves class 12 physics? ›

Electromagnetic waves are those waves in which electric and magnetic field vectors changes sinusoidally and are perpendicular to each other as well as at right angles to the direction of propagation of wave.

What has a frequency of 1000000000 Hz? ›

Electromagnetic Radiation
kHzkiloHertz, one thousand Hertz. (1,000)
MHzMegaHertz, one million Hertz. (1,000,000)
GHzGigaHertz, one billion Hertz. (1,000,000,000)

What are the 7 electromagnetic waves? ›

In order from highest to lowest energy, the sections of the EM spectrum are named: gamma rays, X-rays, ultraviolet radiation, visible light, infrared radiation, and radio waves.

What is the example of electromagnetic wave? ›

Radio waves, microwaves, visible light, and x rays are all examples of electromagnetic waves that differ from each other in wavelength. (a) Longer wavelength; (b) shorter wavelength. Electromagnetic waves are produced by the motion of electrically charged particles.

Who discovered electromagnetic waves? ›

Heinrich Hertz was a brilliant German physicist and experimentalist who demonstrated that the electromagnetic waves predicted by James Clerk Maxwell actually exist. Hertz is also the man whose peers honored by attaching his name to the unit of frequency; a cycle per second is one hertz.

What is the formula for electromagnetic waves? ›

If the frequency of oscillation of the charged particle is f, then it produces an electromagnetic wave with frequency f. The wavelength λ of this wave is given by λ = c/f. Electromagnetic waves transfer energy through space.

What is the SI unit of magnetic field? ›

Magnetic field is denoted by B and H. The SI unit of H is amperes per metre and the SI unit of B is Newtons per metre per ampere or Teslas.

What is electromagnetic waves Class 12 notes? ›

Electromagnetic Waves An electromagnetic wave is a wave radiated by an accelerated or oscillatory charge in which varying magnetic field is the source of electric field and varying electric field is the source of magnetic field.

How many seconds is 1hz? ›

How many seconds in a hertz?
HertzSecondsCycles Per Second
1 hz1 second1 cycle/sec
2 hz0.5 seconds2 cycles/sec
3 hz0.3333 seconds3 cycles/sec
4 hz0.25 seconds4 cycles/sec
18 more rows

What is the value of 1 GHz? ›

One gigahertz equals 1,000,000,000 Hz or 1,000 MHz and has a frequency measurement with periodic 1-second cycles.

What is bigger Hz or GHz? ›

GHz, short for gigahertz, is a unit of frequency equal to one billion hertz. It is commonly used to measure computer processing speed, alternating current, and electromagnetic (EM) frequencies.

Why is it called electromagnetic waves? ›

In other words, EM waves are composed of oscillating magnetic and electric fields. Description: Electromagnetic waves are formed when an electric field comes in contact with a magnetic field. They are hence known as 'electromagnetic' waves.

What are the types of waves? ›

Waves come in two kinds, longitudinal and transverse. Transverse waves are like those on water, with the surface going up and down, and longitudinal waves are like of those of sound, consisting of alternating compressions and rarefactions in a medium.

How do waves carry energy? ›

'Wave' is a common term for a number of different ways in which energy is transferred: In electromagnetic waves, energy is transferred through vibrations of electric and magnetic fields. In sound waves, energy is transferred through vibration of air particles or particles of a solid through which the sound travels.

What are uses of electromagnetic waves? ›

Electromagnetic waves have a vast range of practical everyday applications that includes such diverse uses as communication by cell phone and radio broadcasting, WiFi, cooking, vision, medical imaging, and treating cancer.

What are the 3 types of waves? ›

Based on the orientation of particle motion and direction of energy, there are three categories: Mechanical waves. Electromagnetic waves. Matter waves.

What type of energy is electromagnetic waves? ›

What Is Electromagnetic Energy? Electromagnetic energy is radiant energy that travels in waves at the speed of light. It can also be described as radiant energy, electromagnetic radiation, electromagnetic waves, light, or the movement of radiation.

What is the history of electromagnetic waves? ›

In 1888, Heinrich Hertz, in Karlsruhe, published his experimental validations of Maxwell's equations and forced a conceptual revolution in European theoretical physicists by showing that electromagnetic effects propagate at a finite speed. He also discovered the existence of radio waves.

What is the properties of electromagnetic waves? ›

Basic Properties of Electromagnetic Waves

Property 1: Electromagnetic waves are transverse in nature. Property 2: They propagate by varying electric fields and magnetic fields, such that these two fields are at right angles to each other and at a right angle with the direction of propagation of the wave.

What is the unit of frequency? ›

The number of periods or cycles per second is called frequency. The SI unit for frequency is the hertz (Hz). One hertz is the same as one cycle per second.

What is the frequency of a wave? ›

Frequency describes the number of waves that pass a fixed place in a given amount of time. So if the time it takes for a wave to pass is is 1/2 second, the frequency is 2 per second. If it takes 1/100 of an hour, the frequency is 100 per hour.

What is the speed of EM wave? ›

Electromagnetic radiation is a type of energy that is commonly known as light. Generally speaking, we say that light travels in waves, and all electromagnetic radiation travels at the same speed which is about 3.0 * 108 meters per second through a vacuum.

What is the frequency of an electromagnetic wave? ›

Wavelengths of electromagnetic waves range from about 10^-18 m (one trillionth of a meter) to 100 km, and frequencies range from 3 × 10^26 Hz to 3 ×10^3 Hz.

What is the symbol for magnetic field? ›

Index to magnetic terms & units in the SI
Quantity nameQuantity symbolQuantity symbol
magnetic field strengthHΦ
magnetic flux densityBχρ
magnetic momentmJ
magnetic susceptibilityχM
9 more rows
22 Jul 2014

What is the unit of force? ›

The SI unit of force is the newton, symbol N. The base units relevant to force are: The metre, unit of length — symbol m. The kilogram, unit of mass — symbol kg. The second, unit of time — symbol s.

What is a tesla unit? ›

tesla, unit of magnetic induction or magnetic flux density in the metre–kilogram–second system (SI) of physical units. One tesla equals one weber per square metre, corresponding to 104 gauss. It is named for Nikola Tesla (q.v.).

What are the properties of electromagnetic waves class 12th? ›

  • Electromagnetic waves are propagated by oscillating electric fields and magnetic field oscillation at right angles to each other.
  • These waves travel with speed 3×108ms−1 in vacuum.
  • They are not deflected by electric or magnetic field.
  • They can show interference or diffraction.
  • They are transverse waves.

What is the other term of electromagnetic waves? ›

Electromagnetic Wave synonyms

Radiation (quantized as photons) consisting of. 1. 0. nonparticulate radiation. radiation consisting of waves of energy associated with electric and magnetic fields resulting from the acceleration of an electric charge.

What are electromagnetic waves State its any four characteristics? ›

<br> 2) Electromagnetic waves are transverse in nature. <br> 3) Electromagnetic waves donot require material medium for their propagation. <br> 4) Electromagnetic waves obey principle of superposition of waves. <br> 5) Velocity of E.M waves in vaccum depends on permittivity and permeability of free space.

How many Hz is 2 seconds? ›

Cycle/second to Hertz Conversion Table
Cycle/secondHertz [Hz]
0.1 cycle/second0.1 Hz
1 cycle/second1 Hz
2 cycle/second2 Hz
3 cycle/second3 Hz
7 more rows

What does 2 hertz mean? ›

An example: Frequency describes the number of waves that pass a fixed place in a given amount of time. So for the time it takes for a wave to pass is half a second. Then the frequency is 2 per second or 2 Hertz. If two hundred and forty (240) waves pass in an hour, the frequency is 4 Hertz.

Is 1s the same as Hz? ›

A Hertz is a unit of frequency defined as a reciprocal second, s-1. For example, AC current cycles polarity 60 times per second, so we could call this 60 Hz = 60 s-1.

How many MB is a GHz? ›

Gigahertz to megahertz conversion table
Gigahertz (GHz)Megahertz (MHz)
1 GHz1000 MHz
10 GHz10000 MHz
100 GHz100000 MHz
1000 GHz1000000 MHz
4 more rows

What is GHz in phone? ›

The clock speed determines how many instructions the processor can execute per second. A processor with a 1-Gigahertz (GHz) clock speed can process 1 billion instructions per second. The general rule is that higher clock speeds make for faster phones. You can often see this with more expensive smartphones.

How do you read GHz? ›

What is a Ghz and what does it mean in the computer and CPU speeds

How many hertz is WiFi? ›

WiFi frequency bands are frequency ranges within the wireless spectrum that are designated to carry WiFi: 2.4 GHz and 5 GHz.

How many Hz are in a meter? ›

Wavelength In Metres to Hertz Conversion Table
Wavelength In Metres [m]Hertz [Hz]
1 m299792458 Hz
2 m149896229 Hz
3 m99930819.333333 Hz
5 m59958491.6 Hz
7 more rows

How many hertz are there? ›

It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are commonly expressed in multiples: kilohertz (103 Hz, kHz), megahertz (106 Hz, MHz), gigahertz (109 Hz, GHz), terahertz (1012 Hz, THz).
...
Hertz
In SI base unitss1
6 more rows

What are electromagnetic waves made of? ›

Electromagnetic waves are formed when an electric field (which is shown in red arrows) couples with a magnetic field (which is shown in blue arrows). Magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.

What are 10 electromagnetic waves? ›

EM radiation is classified into types according to the frequency of the wave: these types include, in order of increasing frequency, radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.

How do electromagnetic waves produced? ›

Electromagnetic waves are produced whenever electric charges are accelerated. This makes it possible to produce electromagnetic waves by letting an alternating current flow through a wire, an antenna. The frequency of the waves created in this way equals the frequency of the alternating current.

What are the main parts of a wave? ›

Wave Crest: The highest part of a wave. Wave Trough: The lowest part of a wave. Wave Height: The vertical distance between the wave trough and the wave crest. Wave Length: The distance between two consecutive wave crests or between two consecutive wave troughs.

What type of wave is sound? ›

A longitudinal wave is one where all the particles of the medium (such as gas, liquid or solid) vibrate in the same direction as the wave. Sound waves are longitudinal waves.

Is light a plane wave? ›

Light is a transverse electromagnetic wave, but natural light is generally unpolarized, all planes of propagation being equally probable. If light is composed of two plane waves of equal amplitude by differing in phase by 90°, then the light is said to be circularly polarized.

What kind of wave is light? ›

1. Light as a wave: Light can be described (modeled) as an electromagnetic wave. In this model, a changing electric field creates a changing magnetic field. This changing magnetic field then creates a changing electric field and BOOM - you have light.

Do waves transfer sound? ›

'Wave' is a common term for a number of different ways in which energy is transferred: In electromagnetic waves, energy is transferred through vibrations of electric and magnetic fields. In sound waves, energy is transferred through vibration of air particles or particles of a solid through which the sound travels.

Do waves have mass? ›

The water wave therefore carries momentum even though it has no mass. The water itself has mass, but the wave has no mass. A water wave is not a packet of water traveling along. In fact, the water that the wave is traveling through stays more or less in one place.

What is the term for electromagnetic waves? ›

In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.

What can you say about electromagnetic wave? ›

Electromagnetic waves are not like sound waves because they do not need molecules to travel. This means that electromagnetic waves can travel through air, solid objects and even space. This is how astronauts on spacewalks use radios to communicate. Radio waves are a type of electromagnetic wave.

Why light is called electromagnetic wave? ›

According to Huygens, an expanding sphere of light behaves as if each point on the wave front were a new source of radiation with the same frequency and phase as the preceding one. Because electromagnetic waves have fluctuating electric and magnetic fields, they are called electromagnetic waves.

What are the 7 types of electromagnetic waves and their uses? ›

Behaviour and uses of electromagnetic waves
  • Radio waves. Radio waves are used for communication such as television and radio. ...
  • Microwaves. Microwaves are used for cooking food and for satellite communications. ...
  • Infrared. ...
  • Visible light. ...
  • Ultraviolet radiation.

How are electromagnetic waves classified? ›

Generally, electromagnetic radiation is classified by wavelength into radio wave, microwave, infrared, visible light, ultraviolet, X-rays and gamma rays. The behavior of EM radiation depends on its wavelength.

What is the frequency of a wave? ›

Frequency describes the number of waves that pass a fixed place in a given amount of time. So if the time it takes for a wave to pass is is 1/2 second, the frequency is 2 per second. If it takes 1/100 of an hour, the frequency is 100 per hour.

How do electromagnetic waves travel? ›

Electromagnetic waves differ from mechanical waves in that they do not require a medium to propagate. This means that electromagnetic waves can travel not only through air and solid materials, but also through the vacuum of space.

Why is electromagnetic waves important? ›

Electromagnetic waves are used to transmit long/short/FM wavelength radio waves, and TV/telephone/wireless signals or energies. They are also responsible for transmitting energy in the form of microwaves, infrared radiation (IR), visible light (VIS), ultraviolet light (UV), X-rays, and gamma rays.

Why is it important to study electromagnetic waves? ›

The study of EM is essential to understanding the properties of light, its propagation through tissue, scattering and absorption effects, and changes in the state of polarization.

What are electromagnetic waves used for? ›

Electromagnetic waves have a vast range of practical everyday applications that includes such diverse uses as communication by cell phone and radio broadcasting, WiFi, cooking, vision, medical imaging, and treating cancer.

What causes electromagnetic energy? ›

Electromagnetic radiation is produced whenever a charged particle, such as an electron, changes its velocity—i.e., whenever it is accelerated or decelerated. The energy of the electromagnetic radiation thus produced comes from the charged particle and is therefore lost by it.

Is sound a electromagnetic wave? ›

Sound waves are examples of mechanical waves while light waves are examples of electromagnetic waves. Electromagnetic waves are created by the vibration of an electric charge.

Which type of wave is light? ›

Transverse waves – When the movement of the particles is at right angles or perpendicular to the motion of the energy, then this type of wave is known as a transverse wave. Light is an example of a transverse wave.

What are the types of waves? ›

Waves come in two kinds, longitudinal and transverse. Transverse waves are like those on water, with the surface going up and down, and longitudinal waves are like of those of sound, consisting of alternating compressions and rarefactions in a medium.

Which has longest wavelength? ›

Gamma rays have the longest wavelength. Gamma rays have the longest wavelength.

What are the 7 properties of electromagnetic radiation? ›

The electromagnetic spectrum is generally divided into seven regions, in order of decreasing wavelength and increasing energy and frequency. The common designations are radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV) light, X-rays and gamma-rays.

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