"Electromagnetic waves and their properties" - Short waves. Electromagnetic waves. Radio waves. Produces a chemical effect on photographic plates. Roentgen was the first physicist to receive the Nobel Prize in 1901. The concept of elastic ether has led to irresolvable contradictions. Electromagnetic waves are electromagnetic oscillations propagating in space at a finite speed.

"Physics of electromagnetic waves" - Michael Faraday. 1. What is an electromagnetic field? =. Lesson in physics in grade 11 teacher - Khatenovskaya E.V. MOU secondary school No. 2 with. Krasnoe. This creates an electromagnetic field. . An alternating magnetic field creates an alternating electric field and vice versa. Maxwell expressed the laws of the electromagnetic field as a system of 4 differential equations.

"Transformer" - The lesson uses digital educational resources from http://school-collection.edu.ru. On what and how does the EMF of induction in a coil of a conductor depend. 9. 5. What device should be connected between the AC source and the light bulb? Can a step-up transformer be made into a step-down transformer? II. 13. Write down the important The phenomenon of electromagnetic induction is applied in the transformer.

"Electromagnetic waves" - He graduated from the University of Berlin (1880) and was an assistant to G. Helmholtz. 4.3 Experimental study of EMW. If the optical path difference. interference member. 4.1 EMW generation. Where. Added a well-known principle. The main maximum corresponding. Figure 7.7.

"Electromagnetic field" - Properties of electromagnetic waves: The speed of electromagnetic waves in vacuum is denoted by the Latin letter c: c? 300,000 km/s. What is an electromagnetic wave? The existence of electromagnetic waves was predicted by J. There will be a perturbation of the electromagnetic field. Grade 9 Physics teacher MOU "Secondary School with. Reflector" Lesnova N.P.

"Electromagnetic waves" - Radio waves. Radio waves Infrared Ultraviolet X-rays? How are the vectors E and B oriented with respect to each other in an electromagnetic wave? Obtained using oscillatory circuits and macroscopic vibrators. X-rays. The portion of electromagnetic radiation that is perceived by the eye.

In total there are 14 presentations in the topic

A charged particle, such as an electron, moving at a constant speed does not emit electromagnetic waves. Electromagnetic radiation occurs only with accelerated () movement of charged particles.

For example, X-ray radiation arises as a result of a sharp deceleration of an electron beam colliding with the anticathode.

D Another very important source of electromagnetic waves for understanding many physical processes is an electric dipole that performs harmonic oscillations (Fig. 7.11). The electric moment of the dipole changes in time according to the harmonic law:

,

where
.

The reciprocating displacement of an electric charge is equivalent to the existence of a current element, around which, according to the Biot-Savart-Laplace law, a magnetic field arises. However, the magnetic field in this case will be variable, because. the current element that causes it is variable. An alternating magnetic field causes an alternating electric field - an electromagnetic wave propagates in the medium. At large distances from the dipole (
, - the length of the electromagnetic wave) the wave becomes spherical, in this wave the vectors and perpendicular to each other and to the velocity vector , which in turn is directed along the radius vector . In this case, the vector - tangential to the parallel (in accordance with the Biot-Savart-Laplace law). In the case of an electric dipole emitting an electromagnetic wave, electric charges have an acceleration
.

Similarly, electromagnetic radiation arises when the electron shells are displaced relative to the nuclei of atoms. Such a displacement can occur either as a result of the action of an alternating electric field, or as a result of thermal vibrations of the atoms of a substance. The latter mechanism is the cause of the so-called "thermal cure" of heated bodies.

It is interesting to note that during periodic deformations of the magnetic dipole, an electromagnetic wave is also emitted.

H and fig. 7.12 shows a cylindrical magnet, magnetized along the axis. Longitudinal deformation of the cylinder (at a constant radius) will lead to a change in the magnetization and magnetic moment:

.

The periodic deformation of the magnetized cylinder is accompanied by a periodic change in the magnetic moment and the emission of an electromagnetic wave. However, in this case, the vector directed tangentially to the meridian, and the vector - tangent to the parallel on the spherical wave surface.

Lecture 8. The principle of relativity in electrodynamics

Relativistic transformation of electromagnetic fields, charges and currents. Electric field in different reference systems. Magnetic field in different reference systems. Electromagnetic field in different reference systems. Proof of the invariance of electric charge. Invariance of Maxwell's equations with respect to Lorentz transformations.

8.1. Relativistic transformation of electromagnetic fields, charges and currents

8.1.1. Electric field in different reference systems

As is known, mechanical phenomena in all inertial frames of reference (frames of reference moving relative to each other in a straight line and uniformly) proceed in the same way. At the same time, it is impossible to establish which of these systems is at rest and which are moving, and therefore one can only speak of the relative motion of these systems with respect to each other.

With the help of electromagnetic phenomena, it is also impossible to obtain evidence for the existence of absolute motion, and therefore, evidence for the existence of absolute reference systems. All frames of reference, moving relative to each other in a straight line and uniformly, are equal, and in all these frames of reference the laws of electromagnetic phenomena are the same. This is the principle of relativity for electromagnetic phenomena: electromagnetic phenomena proceed in the same way in all inertial frames of reference. Therefore, it is possible to formulate the principle of relativity of the division of the electromagnetic field into an electric field and a magnetic field: a separate consideration of the electric and magnetic fields has only a relative meaning.

Mutual transformations of electric and magnetic fields caused by the change of fields in time were considered earlier. Similar phenomena take place when the electromagnetic field moves relative to the observer.

Assume that a positive charge is moving in a magnetic field in a vacuum. From the point of view of the first observer (stationary with respect to the magnetic field), the Lorentz force acts on the charge:

,

where q is the charge value;

- magnetic field induction;

v is the charge rate;

α is the angle between the direction of the magnetic field induction vector and the particle velocity vector.

The direction of this force is perpendicular to and , coincides with the direction of the vector product
.

O with respect to the second observer moving along with the charge, the charge is stationary, although the same force acts on it F. But if a force proportional to the magnitude of the charge acts on a stationary charge, then this means that there is an electric field. The intensity of such a field can be determined by the formula

. (8.1)

The intensity vector of such an electric field coincides in direction with the direction of the force F, i.e. the electric field strength vector is perpendicular to the vectors and (Fig. 8.1).

Thus, the electromagnetic field depends on the frame of reference. If in any frame of reference there is one magnetic field, then in other frames of reference moving relative to the first, there are both magnetic and electric fields.

R Let us consider the behavior of the electric field in different frames of reference. We will consider the frame of reference in which electric charges or conductors with charges are at rest as a fixed frame of reference - the system
. A frame of reference moving at some speed v relative to the reference frame K, moving reference frame, frame -
(Fig. 8.2).

Let us assume that in the reference frame
there are two motionless, uniformly charged parallel plates carrying charges with a density
and
. The plates are squares with side "b", parallel to the plane
. The distance between the plates  0 is small compared to the size of the plates "c". In this regard, the electric field between the plates can be considered uniform. The plates are in a vacuum, i.e.
. The magnitude of the electric field measured by an observer in
- the system is equal to
. In this case, the component of the electric field strength vector, parallel to the axis
. In the frame of reference
moving at a speed in the direction
, according to the Lorentz transformations, the distance decreases in once. Since the distance between planes does not affect the magnitude of the vector , then the electric field does not change in this direction. The pattern of electric field lines for this case is shown in Fig. . 8.3.

In another case (Fig. 8.4), when the plates are parallel to n flatness
in system
, the length of the longitudinal sides is reduced and the squares become rectangles flattened in the direction of motion. Since the electric charge is an invariant quantity (does not change) with respect to the choice of reference frame, i.e.
, then with the charge unchanged, the surface area decreases, therefore, in times the surface charge density increases
. Therefore, the electric field strength in this direction will be equal to

, (8.2)

t .e. the transverse component of the electric field strength increases in times compared to the fixed frame of reference. As a result of this, the pattern of force lines of the electric field of a positive point charge will change (Fig. 8.5). They thicken in a direction perpendicular to the direction of charge movement.

It can be shown that the change in the electric field strength in the ZOX plane will also occur similarly.

The results obtained can be presented in a different form. Let there be two frames of reference
and . System attitude is moving system
at a constant speed v parallel to the X axis (Fig. 8.6). In system
there is a magnetic field, which is characterized by the intensity vector H. At the considered point of space "A", the components of the magnetic field strength vector are respectively equal to
. Then at the same point, but in the system , due to the movement, an electric field will appear with a strength E, whose components are respectively equal
. Applying formula (8.1) to the individual components of the electric field strength, we obtain

(8.3)

If in the system there is also an electric field, then the resulting electric field in the system
will be characterized by the resulting tension vector E, whose components are respectively equal

(8.4)

We emphasize that v is the speed of the system regarding the system
.

8.1.2. Magnetic field in different reference systems

It is known that when electric charges move (when an electric field moves, in the presence of a current) a magnetic field arises in space.

To determine this field, consider a charge +q moving relative to the first observer with a speed v. Such a charge creates a magnetic field with intensity

, (8.5)

where r is the radius vector drawn from the charge to the considered point in space.

Since in expression (8.5)
- induction of the electric field created by the charge at the considered point A, which is related to the electric field strength by the relation
, then, taking into account the direction of the vector D(whose direction coincides with the direction of the radius vector r at a given point) can be written

. (8.6)

Expression (8.6) is the modulus of the vector product, i.e.

. (8.7)

Relation (8.7) allows us to assert that the vector H perpendicular to the vectors v and D.

For the second observer moving along with the charge, there is only an electric field whose induction vector is equal to D. Thus, in a fixed frame of reference, there is only an electric field, and in a moving frame of reference, there are electric and magnetic fields (Fig. 8.7).

At we establish the relationship between the characteristics of the electric and magnetic fields. For which we introduce two frames of reference, one of which (K) moves relative to the other (K ​​") in the direction X 1 (Fig. 8.8). We assume that the charge is at rest in the reference frame K". In this case, the electric field of the selected charge will move relative to the system K with the speed "-v". Using formula (8.6) for the components of the magnetic field strength vector (taking into account the sign of the velocity v), we will have

(8.8)

If in the system K " there is also a magnetic field with strength components
, then the resulting magnetic field at the considered point in space will be characterized by the components of the intensity vector of this magnetic field:

(8.9)

In relations (8.9), the velocity v is the velocity of the system K (in which there is a magnetic field with components of the strength vector
) relative to the system K " .

It should be noted that relations (8.9) for the transformation of magnetic fields are valid only when the motion occurs at velocities much less than the speed of light in vacuum.

8.1.3. Electromagnetic field in different reference systems

The expression for the Lorentz force acting on a point charge in an electromagnetic field was obtained taking into account the requirements of the invariance of the relativistic equation of motion:

.

Consequently, the expression for the Lorentz force must also be relativistically invariant, i.e. have the same form in all inertial frames of reference. Thus, if there are two frames of reference K and K " , one of which, for example K " , moves uniformly and rectilinearly with a speed v relative to the frame K, then the expressions for the Lorentz force in these frames of reference will have the form

(8.10)

. (8.11)

Using the relativistic invariance of the expression for the Lorentz force (8.10) and (8.11) and taking into account the transformation formulas for forces when moving from one inertial frame to another, one can obtain the relationship between the vectors of the electric and magnetic fields of the electromagnetic field in different frames of reference. A special case of such transformations was considered earlier.

The force transformation formulas have the form

(8.12)

(8.13)

, (8.14)

where v is the relative speed of the frames of reference;

u x , u y , u z are the projections of the velocity of the charged particle on the corresponding coordinate axes;

.

Let us substitute in the formula (8.13) instead of F y and F y " their expression (8.10), (8.11), we will have

. (8.15)

Eliminating from formula (8.15) the quantities and using formulas for adding velocities in the theory of relativity
and
, grouping all the terms on the left side of relation (8.15), we find

(8.16)

Equality (8.16) is valid for arbitrary values and . Consequently, the expressions in brackets (8.16) are individually equal to zero. Equating them to zero, we obtain the transformation formulas for the electromagnetic field vectors:

(8.17)

(8.18)

(8.19)

Similarly, based on relation (8.14), one can obtain transformation formulas for other components of the vectors E and B:

(8.20)

(8.21)

(8.22)

Derivation of the transformation formula for the projection of the electric field strength vector ( E) E x can be carried out using the relation

. (8.23)

Proceeding in the same way as in the previous cases, we reduce relation (8.23) to the form

where
.

Using formulas (8.19) and (8.22), we find that

. (8.25)

Thus, the transformation formulas for the electromagnetic field vectors have the form

(8.26)

The formulas for transforming the vectors of the electromagnetic field (8.26) make it possible to determine the vectors of this field in any inertial frame of reference, if they are known in any one of them.

8.1.4. Proof of the invariance of electric charge

Let a positive electric charge move in
system, as shown in Fig. 8.9, across an electric field with strength . Then in the system moving at a speed , a force acting on a stationary charge in this system

. (8.27)

It is known from relativistic dynamics that in the system (on a moving material particle under the condition
) the force acts

. (8.28)

Since the left parts of equalities (8.27) and (8.28) are equal, the right parts are also equal, which is possible when
. Such a conclusion is consistent with the assumption made above about the invariance of the charge and can be considered as a simple proof of this statement.

It should be noted that the volume charge density  changes in accordance with the Lorentz transformations. This is because the bulk charge density

.

With a uniform charge distribution

.

The volume during the transition from one inertial frame to another changes, according to the Lorentz transformations, according to the law

.

Therefore, when moving from one inertial frame of reference to another, the volumetric charge density changes according to the law:

. (8.29)

In the transition from one inertial frame to another for the electric charge, we obtain

. (8.30)

It can be seen from relation (8.30) that, indeed, when moving from one frame of reference to another, the charge remains a constant value, i.e. the electric charge is invariant to the relative Lorentz transformations.

It is known that the Joule-Lenz law in differential form in a fixed reference frame reflects the dependence of the current density on the electric field strength:

.

It can be shown that the current density j in a stationary medium in which charges move at a speed v in an electromagnetic field with strengths E and B, changes in accordance with the Lorentz transformations according to the law

, (8.31)

where the magnitudes of the vectors E and B(same as vectors E " and B " ) are defined in the same way as in classical electrodynamics, i.e., in essence, by equalities (8.10 and 8.11).

Electromagnetic waves The concept of electromagnetic waves The formation of electromagnetic waves Types of electromagnetic radiation, their properties and application Completed by a student of the TE-21 group: Andrey Sizikov

The nature of an electromagnetic wave An electromagnetic wave is a distribution in space over time of variable (vortex) electric and magnetic fields.

Formation of an EMW wave Electromagnetic waves are studied by oscillating charges, and it is essential that the speed of movement of such charges varies with time, i.e., they move with acceleration.

Historical note Maxwell was deeply convinced of the reality of electromagnetic waves, but did not live to see their experimental discovery. Only 10 years after his death, electromagnetic waves were experimentally obtained by Hertz. In 1895, A. S. Popov demonstrated the practical application of EMW for radio communications. Now we know that all the space around us is literally permeated with electromagnetic waves of different frequencies.

Electromagnetic waves of different frequencies differ from each other. Currently, all electromagnetic waves are divided by wavelength (and, accordingly, by frequency) into six main ranges: radio waves, infrared radiation, visible radiation, ultraviolet radiation, x-rays, γ radiation

Radio waves are obtained with the help of oscillatory circuits and macroscopic vibrators. Properties: radio waves of different frequencies and with different wavelengths are absorbed and reflected by media in different ways. exhibit the properties of diffraction and interference. Application: Radio communication, television, radar.

Infrared radiation (thermal) Radiated by the atoms or molecules of matter. Infrared radiation is emitted by all bodies at any temperature. Properties: passes through some opaque bodies, as well as through rain, haze, snow, fog; produces a chemical action (photoblasts); being absorbed by the substance, heats it; invisible; capable of interference and diffraction phenomena; registered by thermal methods. Application: Night vision device, forensics, physiotherapy, in industry for drying products, wood, fruits.

Visible Radiation The portion of electromagnetic radiation that is visible to the eye. Properties: reflection, refraction, affects the eye, capable of the phenomenon of dispersion, interference, diffraction.

Ultraviolet radiation Sources: Discharge lamps with quartz tubes. Radiated by all solids, in which t 0> 1 OOO ° C, as well as luminous mercury vapor. Properties: High chemical activity, invisible, high penetrating power, kills microorganisms, in small doses it has a beneficial effect on the human body (sunburn), but in large doses it has a negative effect, changes the development of cells, metabolism. Application: in medicine, in industry.

X-rays are emitted at high accelerations of electrons. Properties: interference, X-ray diffraction on a crystal lattice, high penetrating power. Irradiation in high doses causes radiation sickness. Application: in medicine for the purpose of diagnosing diseases of internal organs; in industry to control the internal structure of various products.

γ-radiation Sources: atomic nucleus (nuclear reactions). Properties: Has a huge penetrating power, has a strong biological effect. Application: In medicine, production (γ-defectoscopy).

The influence of electromagnetic radiation on living organisms electromagnetic radiation with a frequency of 50 Hz, which is created by the wires of the alternating current network, with prolonged exposure causes drowsiness, signs of fatigue, headaches. In order not to increase the effect of household electromagnetic radiation, experts recommend not to place electrical appliances operating in our apartments close to each other - a microwave oven, an electric stove, a TV, a washing machine, a refrigerator, an iron, an electric kettle. The distance between them should be at least 1.5-2 m. Your beds should be removed from the TV or from the refrigerator at the same distance.

The influence of electromagnetic radiation on living organisms Radio waves Infrared Ultraviolet X-ray γ-radiation Homework: Write in a notebook about the effect of each radiation on humans, animals, plants.

Questions for consolidation 1. What is called an electromagnetic wave? 2. What is the source of an electromagnetic wave? 3. How are the vectors E and B oriented relative to each other in an electromagnetic wave? 4. What is the propagation speed of electromagnetic waves in the air?

Questions for consolidation 5. What conclusions regarding electromagnetic waves followed from Maxwell's theory? 6. What physical quantities change periodically in an electromagnetic wave? 7. What relationship between the wavelength, its speed, period and frequency of oscillations are valid for electromagnetic waves? 8. Under what condition will the wave be intense enough to be registered?

Questions to reinforce 9. When and by whom were electromagnetic waves first received? 10. Give examples of the application of electromagnetic waves. 11. Arrange in ascending order of wavelength electromagnetic waves of various nature: 1) infrared radiation; 2) X-ray radiation; 3) radio waves; 4) γ-waves.

• The concept of electromagnetic waves

• Formation of electromagnetic waves

• Types of electromagnetic radiation, their properties and application

The nature of the electromagnetic wave

• An electromagnetic wave is a distribution in space over time of variable (vortex) electric and magnetic fields.

Formation of an EMW wave

• Electromagnetic waves are studied by oscillating charges, and it is essential that the speed of movement of such charges varies with time, i.e. they move with speed.

• An electromagnetic field is emitted in a noticeable way, not only when the charge fluctuates, but also with any rapid change in its speed. Moreover, the intensity of the radiation of the wave is the greater, the greater the acceleration with which the charge moves.

• The vectors E and B in an electromagnetic wave are perpendicular to each other and are perpendicular to the direction of wave propagation.

• The electromagnetic wave is transverse

History reference

• Maxwell was deeply convinced of the reality of electromagnetic waves, but did not live to see their experimental discovery.

• Only 10 years after his death, electromagnetic waves were experimentally obtained by Hertz.

• In 1895 A.S. Popov demonstrated the practical application of EMW for radio communications.

• Now we know that all the space around us is literally permeated with electromagnetic waves of different frequencies.

Electromagnetic waves of different frequencies differ from each other.

• Currently, all electromagnetic waves are divided by wavelength (and, accordingly, by frequency) into six main ranges: radio waves, infrared radiation, visible radiation, ultraviolet radiation, x-rays, γ-radiation

radio waves

• Obtained using oscillatory circuits and macroscopic vibrators.

• Properties:

• radio waves of different frequencies and with different wavelengths are absorbed and reflected by media in different ways.

• exhibit the properties of diffraction and interference.

• Application: Radio communication, television, radar.

Infrared radiation (thermal)

• Radiated by atoms or molecules of matter. Infrared radiation is emitted by all bodies at any temperature.

• Properties :

• passes through some opaque bodies, as well as through rain, haze, snow, fog;

• produces a chemical action (photoblasts);

• being absorbed by the substance, heats it;

• invisible;

• capable of interference and diffraction phenomena;

• registered by thermal methods.

• Application : Night vision device, forensics, physiotherapy, in the industry for drying products, wood, fruits.

Visible radiation

• The portion of electromagnetic radiation that is perceived by the eye.

• Properties:

• reflection,

• refraction,

• affects the eye

• capable of dispersion,

• interference,

• diffraction.

Ultraviolet radiation

• Sources: gas discharge lamps with quartz tubes. Radiated by all solids, in which t0> 1 000 ° C, as well as luminous mercury vapor.

• Properties: High chemical activity, invisible, large penetrating power, kills microorganisms, in small doses it has a beneficial effect on the human body (sunburn), but in large doses it has a negative effect, changes cell development, metabolism.

• Application: in medicine, in industry.

X-rays

• They are emitted at high accelerations of electrons.

• Properties: interference, x-ray diffraction on a crystal lattice, large penetrating power. Irradiation in high doses causes radiation sickness.

• Application: in medicine for the purpose of diagnosing diseases of internal organs; in industry to control the internal structure of various products.

γ radiation

• Sources: atomic nucleus (nuclear reactions).

• Properties: Has a huge penetrating power, has a strong biological effect.

• Application: In medicine, production (γ-defectoscopy).

• electromagnetic radiation with a frequency of 50 Hz, which is created by AC wires, causes drowsiness, signs of fatigue, and headaches with prolonged exposure.

In order not to increase the effect of household electromagnetic radiation, experts recommend not to place electrical appliances operating in our apartments close to each other - a microwave oven, an electric stove, a TV, a washing machine, a refrigerator, an iron, an electric kettle. The distance between them should be at least 1.5-2 m. Your beds should be removed from the TV or from the refrigerator at the same distance.

The influence of electromagnetic radiation on living organisms

• radio waves

• infrared

• ultraviolet

• x-ray

• γ radiation

Questions for consolidation

• What is an electromagnetic wave?

• What is the source of an electromagnetic wave?

• How are the vectors E and B oriented with respect to each other in an electromagnetic wave?

• What is the speed of propagation of electromagnetic waves in air?

Questions for consolidation

• 5. What conclusions regarding electromagnetic waves followed from Maxwell's theory?

• 6. What physical quantities change periodically in an electromagnetic wave?

• 7. What relationship between the wavelength, its speed, period and frequency of oscillations are valid for electromagnetic waves?

• 8. Under what condition will the wave be intense enough to be registered?

Questions for consolidation

• 9. When and by whom were electromagnetic waves first received?

• 10. Give examples of the application of electromagnetic waves.

• 11. Arrange in ascending order of wavelength electromagnetic waves of various nature: 1) infrared radiation; 2) X-ray radiation; 3) radio waves; 4) γ-waves.

In this paper, such issues as the concept of waves, electromagnetic waves and their experimental detection, the properties of electromagnetic waves, the scale of electromagnetic waves were considered.

Electromagnetic waves is the process of propagation of an electromagnetic field in space.

The existence of electromagnetic waves was theoretically predicted by the English physicist J.K. Maxwell. It is known that an electric current generates a magnetic field (Oersted's experiment), a changing magnetic field generates an electric current (Faraday's experiment). With these experimental facts in mind, the English physicist Maxwell created the theory of electromagnetic waves. Based on his equations, he came to the conclusion that in vacuum and dielectrics, arbitrary perturbations of the electromagnetic field propagate in the form of an electromagnetic wave.

Thus, the accelerated movement of electric charges leads to the emergence of electromagnetic waves - interrelated changes in the electric and magnetic fields. According to Maxwell: an alternating magnetic field generates a vortex electric (the phenomenon of electromagnetic induction), and an alternating electric field generates a vortex magnetic (magnetoelectric induction). As a result, a single electromagnetic field arises in neighboring regions of space.

According to Maxwell:

An electromagnetic wave is transverse, since the vectors of the electric field and the magnetic field are perpendicular to each other and lie in a plane perpendicular to the direction of wave propagation, their propagation velocity in vacuum is approximately 300,000 km / s, this wave carries energy;

Electromagnetic waves, like other waves, carry energy. This energy is contained in the propagating electric and magnetic fields;

An electromagnetic wave must have momentum, and therefore exert pressure on bodies.

For the first time experiments with electromagnetic waves were carried out in 1888 by G. Hertz. With the help of a spark gap and a receiver similar to it, he received and registered electromagnetic waves, discovered their reflection and refraction. Further studies of electromagnetic waves showed that they have the ability to experience reflection, refraction, diffraction, interference and polarization.

The credit for the practical use of electromagnetic waves in radio communications belongs to the Russian physicist A.S. Popov.

The meaning of Maxwell's theory:

1. Maxwell showed that the electromagnetic field is a combination of interconnected electric and magnetic fields.

2. Predicted the existence of electromagnetic waves propagating from point to point with a finite speed.

3. He showed that light waves are electromagnetic waves, and in their physical nature is no different from other electromagnetic waves - radio waves, infrared, ultraviolet, x-ray and gamma radiation.

4. Linked together electricity, magnetism and optics.