Electromagnetic waves/radiation properties?

[iantresman]

As I understand it, light is an electromagnetic wave consisting of an oscillating electric and magnetic fields perpendicular to each other.

1. Are there experiments that will demonstrate (a) there is an electric field present? Stark effect? (b) a magnetic field, (c) that they are perpendicular to each other.
2. Am I right in thinking that an electric field between two charges, and a magnetic field between the poles of a magnetic, do not oscillate?
3. Am I right in thinking that in an electromagnetic field, the electric and magnetic field components have no charges or poles terminating them?
4. I believe that the electric field between charges has direction, and designated +ve and -ve ends. It is meaningful to designate direction to the electric field in EM, in which case does light travel +ve or -ve end first, or is it perhaps up/down?
5. Does an EM wave have length?
6. If an EM wave is oscillating, I believe that when the magnetic field is 0, then the electric field is at a maximum. Since EM is very strong force, does it seek out, or is affected by charged particles?

 

[phyzguy]

As I understand it, light is an electromagnetic wave consisting of an oscillating electric and magnetic fields perpendicular to each other.

Maxwell's equation, which describe electromagnetic waves, have been known for over 100 years and are very well understood. They have been validated by an enormous number of experiments. Many of the devices you are familiar with, like cell phones and computers have been designed with the assumption that Maxwell's equations are valid. If they weren't most of these devices wouldn't function.

Are there experiments that will demonstrate (a) there is an electric field present? Stark effect? (b) a magnetic field, (c) that they are perpendicular to each other.

The antenna in your cell phone (or any radio) works because the charges in the antenna respond to the electric field in the passing EM wave. If there were no electric field, the charges wouldn't move and there would be no current for the amplifier to amplify and turn into a signal, so your phone wouldn't work. Other devices, like Hall effect sensors, can measure the magnetic field in the wave.

Am I right in thinking that an electric field between two charges, and a magnetic field between the poles of a magnetic, do not oscillate?

Yes, if the charges and the magnet do not move.

Am I right in thinking that in an electromagnetic field, the electric and magnetic field components have no charges or poles terminating them?

Yes.

I believe that the electric field between charges has direction, and designated +ve and -ve ends. It is meaningful to designate direction to the electric field in EM, in which case does light travel +ve or -ve end first, or is it perhaps up/down?

EM waves have two possible polarizations. As you said, E and B are perpendicular. The wave travels in a direction perpendicular to both E and B. Given two perpendicular vectors E and B, there are two directions perpendicular to both of them, and the E-M wave can travel in either direction. this is why there are two possible polarizations.

Does an EM wave have length?

Yes. The distance between peaks of the E-field or B-field is the wavelength of the wave.

If an EM wave is oscillating, I believe that when the magnetic field is 0, then the electric field is at a maximum. Since EM is very strong force, does it seek out, or is affected by charged particles?

It is certainly affected by charged particles. This is why E-M waves do not travel through conductors, and why E-M waves are scattered by isolated charges.

 

[sophiecentaur]

If an EM wave is oscillating, I believe that when the magnetic field is 0, then the electric field is at a maximum. Since EM is very strong force, does it seek out, or is affected by charged particles?

If your fields are part of a wave propagation in Free Space (distant from its source) the E and H fields are In Phase. In the near field (very near an antenna, for instance) they are in Quadrature (almost exactly). Between the two cases, there is an intermediate situation (a bit of both).

 

[Drakkith]

I believe that the electric field between charges has direction, and designated +ve and -ve ends. It is meaningful to designate direction to the electric field in EM, in which case does light travel +ve or -ve end first, or is it perhaps up/down?

Neither. The wave propagates in a direction perpendicular to the field vectors (the things are represented by field lines). Take a look at the following diagram:

https://upload.wikimedia.org/wikipedia/commons/d/da/Felder_um_Dipol.jpg

Notice that the field lines form loops and these loops are oriented such that the arrows always point in a direction perpendicular to the direction of travel, which is approximately away from the center of the antenna, but not exactly since the antenna isn't point-size.

Does an EM wave have length?

The EM certainly has a wavelength, which is the distance between "peaks" or "troughs" if you look at a diagram of the wave, but the distance that the wave as a whole occupies can be quite large and depends on how long the source has been transmitting/emitting. The EM waves transmitted by the New Horizons spacecraft back to NASA are at least 5 light-hours long since it is at least that far away from us. And if it's been continuously transmitting data for more than 5 hours then the initial wavefront is even further from the spacecraft (the part of the wavefront that doesn't hit Earth or another object just continues on unimpeded).

If an EM wave is oscillating, I believe that when the magnetic field is 0, then the electric field is at a maximum. Since EM is very strong force, does it seek out, or is affected by charged particles?

As far as I know, the magnetic and electric fields are both in sync with each other. That is, both are maximum at the same time and zero at the same time.

 

[phyzguy]

As far as I know, the magnetic and electric fields are both in sync with each other. That is, both are maximum at the same time and zero at the same time.

That's correct. I missed this in the OP, thanks for catching this. This Wikipedia page has a nice animation.

 

[tech99]

Are there experiments that will demonstrate (a) there is an electric field present? Stark effect? (b) a magnetic field, (c) that they are perpendicular to each other.

The electric field of an EM wave can easily be measured by using a short dipole connected to an RF voltmeter, and the magnetic field by using a small loop in the same way. The two antennas give maximum response when aligned with their respective fields. So for example, if the wave is vertically polarised, the electric field is vertical and the electric probe will be vertical. The loop will be in the vertical plane and edge-on the the incoming wave, responding to a horizontal magnetic field.

 

[ZapperZ]

As I understand it, light is an electromagnetic wave consisting of an oscillating electric and magnetic fields perpendicular to each other.

1. Are there experiments that will demonstrate (a) there is an electric field present? Stark effect? (b) a magnetic field, (c) that they are perpendicular to each other.

Particle accelerators from all over the world. The accelerating structures are either standing wave or traveling wave waveguides. The E-field in the EM wave accelerates the charge particles.

Zz.

 

[tech99]

Particle accelerators from all over the world. The accelerating structures are either standing wave or traveling wave waveguides. The E-field in the EM wave accelerates the charge particles.

Zz.

But for a waveguide, the field structure is different to free space. We have a longitudinal field component, E or H, and I presume this is what causes the particles to accelerate.

 

[ZapperZ]

But for a waveguide, the field structure is different to free space. We have a longitudinal field component, E or H, and I presume this is what causes the particles to accelerate.

Yeah?

OP wanted evidence that EM waves have electric field. What’s wrong with the example?

Zz.