A few questions on electricity and magnetism and EM fields

[The Cat]

Hello:

Many many years ago I walked away from community college with an associates degree in physics, and despite my fondness for the subject, I had to put it aside for other things.

I recently happened upon something that lead me to realize how much I had forgotten, and so I've decided to brush off the old calculator and textbooks and delve back into the subject.

Unfortunately I don't think I'm as bright as I used to be and I was wondering if someone could refresh my memory on a few basic things.

1. What is the difference between an electric and magnetic field generated by a charged particle such as an electron or proton, and the electromagnetic field of photons? Why doesn't the electromagnetic field of visible light affect free electrons, protons and other charged particles? I think I recall something about it being too weak but I'm not sure.

2. Why did Ampere define the amp the way he did? Did he intend the force between the two wires to be 2X10^(-7) Newtons per meter length for some reason or did he define it based on the opinion that the wires should be 1 meter apart to keep with the developing SI at the time?

3. And this one is on behalf of my brother who made me realize I had never thought about this before...why is light at infrared wavelengths such a good vector of heat across such a broad spectrum of materials? For example, microwaves heat water by causing the molecules to oscillate, but there are many materials you could stick in a microwave that are invisible to the microwaves, and while the microwaves are leaving the source as energy, they aren't leaving it as heat energy, as far as I understand, but infrared photons are?

 

[pallidin]

Hello:

Many many years ago I walked away from community college with an associates degree in physics, and despite my fondness for the subject, I had to put it aside for other things.

I recently happened upon something that lead me to realize how much I had forgotten, and so I've decided to brush off the old calculator and textbooks and delve back into the subject.

Unfortunately I don't think I'm as bright as I used to be and I was wondering if someone could refresh my memory on a few basic things.

1. What is the difference between an electric and magnetic field generated by a charged particle such as an electron or proton, and the electromagnetic field of photons? Why doesn't the electromagnetic field of visible light affect free electrons, protons and other charged particles? I think I recall something about it being too weak but I'm not sure.

2. Why did Ampere define the amp the way he did? Did he intend the force between the two wires to be 2X10^(-7) Newtons per meter length for some reason or did he define it based on the opinion that the wires should be 1 meter apart to keep with the developing SI at the time?

3. And this one is on behalf of my brother who made me realize I had never thought about this before...why is light at infrared wavelengths such a good vector of heat across such a broad spectrum of materials? For example, microwaves heat water by causing the molecules to oscillate, but there are many materials you could stick in a microwave that are invisible to the microwaves, and while the microwaves are leaving the source as energy, they aren't leaving it as heat energy, as far as I understand, but infrared photons are?

Regarding question 1: A photon is not charged.

 

[RocketSci5KN]

Regarding question 1: A photon is not charged.

A powerful enough laser will rip one or more electrons from even stable atoms - the electric fields of the photons superimpose to create E fields no electron can ignore...

 

[jtbell]

2. Why did Ampere define the amp the way he did?

I don't think Ampere himself defined the ampere. It's just named after him. SI units are practical units which are intended to be precisely reproducible in a laboratory. It's relatively easy to measure the force between two current-carrying wires precisely, and gives better precision than defining the coulomb some other way and then defining 1 A = 1 C/s.

 

[pallidin]

A powerful enough laser will rip one or more electrons from even stable atoms - the electric fields of the photons superimpose to create E fields no electron can ignore...

OK, but can we clarify that a photon has no charge?

 

[BruceW]

In answer to 3: The temperature of objects on Earth is such that most blackbody radiation is in the infrared range. Therefore in most textbooks, only infrared is mentioned when talking about heat. But actually all wavelengths are given off as heat (its just that most of it is infrared).

 

[chrisbaird]

1. You are confused. Photons don't create electromagnetic fields. Photons are the electromagnetic field. Charged particles create electromagnetic fields, which is the same as saying charged particles emit photons. Photons have no mass and mediate the electromagnetic force, whereas electrons and protons have mass and experience forces.

Visible light does effect charged particles. That's why mirrors reflect, lenses focus, and everything has color. Perhaps you mean: Why doesn't visible light permanently damage objects? Visible light has less energy per photon than ultraviolet, x-rays. But visible light can still do plenty of damage if you have enough of it.

 

[RocketSci5KN]

OK, but can we clarify that a photon has no charge?

Photons have no charge. They are oscillating E and B fields, 90 degrees to each other, with the vector direction for each perpendicular to the direction of the photons travel. Or so I recall from a laser class in college.