# Electric & Magnetic Fields in EM Waves: Explained

• Samujawal
In summary, the electric and magnetic fields in an electromagnetic wave are in phase because of the relationship between the electric and magnetic fields, which are directly proportional to each other and their rate of change. This behavior is observed in free space, but may differ in materials depending on their conductivity and frequency. This can be explained through Faraday's Law and Ampere's Law, and the wave equation derived from Maxwell's equations.
Samujawal
Why are electric and magnetic fields in an electromagnetic wave in phase? Can somebody please explain that?

I'd imagine it has to do with the fact that the electric field created is directly proportional to the rate of change of the magnetic field, and the magnetic created is directly proportional to the rate of change of the electric field, but I feel this is a very hand-wavy answer, and I await a more knowledgeable person to provide a more thorough answer.

I think that it has got something to do with Faraday's Law and Ampere's law. But as you said, let's wait for somebody to give a robust answer.

In general E and B field are not always in phase. They are in phase if there's no net free charge flow in the medium through which the wave propagates, example of such media are dielectric and vacuum (this one not really a medium though). If there is free charge fluctuation such as in conductors the wavevector wouldn't be real anymore (more precisely there is attenuation to the field) and magnetic and electric fields wouldn't be in phase.

Actually the response of material depends on the incoming field frequency, the determining quantity is σ/(εω) where σ, ε, and ω are conductivity, permittivity, and frequency respectively. The bigger that quantity the closer the material to behave as a conductor. For example water can behave as a conductor within certain frequency region.

Samujawal said:
Why are electric and magnetic fields in an electromagnetic wave in phase? Can somebody please explain that?

For a wave in free space, they are in phase, You can justify that by looking at the solution to the wave equation, starting with Maxwells equations. See this link.

## 1. What are electric and magnetic fields?

Electric and magnetic fields are two components of electromagnetic waves. They are invisible forces that exist around electrically charged particles and magnets, respectively. These fields are responsible for the transmission and absorption of electromagnetic energy, which includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.

## 2. How are electric and magnetic fields related?

Electric and magnetic fields are closely related and are often considered as two parts of the same phenomenon. A change in one field will always produce a corresponding change in the other. This relationship is described by Maxwell's equations, which explain how electric and magnetic fields interact and propagate through space as electromagnetic waves.

## 3. What are the properties of electric and magnetic fields?

Electric and magnetic fields have several properties, including strength, direction, and frequency. The strength of the fields is measured in units of volts per meter (V/m) for electric fields and teslas (T) for magnetic fields. The direction of the fields is perpendicular to each other and the direction of propagation of the electromagnetic wave. The frequency of the fields determines the type of electromagnetic wave, with lower frequencies corresponding to longer wavelengths and higher frequencies corresponding to shorter wavelengths.

## 4. How do electric and magnetic fields interact with matter?

Electric and magnetic fields can interact with matter in different ways depending on the properties of the material. Some materials, such as metals, can reflect and absorb electromagnetic waves, while others, like glass, can partially transmit and refract them. The interaction between electric and magnetic fields and matter is the basis for many technologies, including wireless communication and medical imaging.

## 5. Are electric and magnetic fields harmful to humans?

The effects of electric and magnetic fields on human health are a topic of ongoing research and debate. While high levels of exposure to these fields, such as those found near power lines, can have adverse effects, the electromagnetic fields produced by everyday devices, such as cell phones and microwaves, are generally considered safe. The World Health Organization and other regulatory bodies have established guidelines to limit exposure to electromagnetic fields in order to ensure public safety.

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