Inducing a current through moving charges or electromagnetic radiation

[mavc]

I have recently found a circuit schematic that can pick up radio signals without the need of a battery.

Is this an example of electromagnetic induction? If so, how much voltage/current is induced?

Does it change the properties of the electromagnetic wave, e.g. energy, wavelength, etc?

Thanks,
Anna.

 

[Antiphon]

If it is a crystal radio, it is not what we would call induction but technically yes it might be.

The term Induction usually refers to processes ocurring around nearby arrangements of conductors and/or magnets. Examples are motors and electric transformers.

If the radio uses a loop antenna then technically it is receiving via induction. If the antenna is not a loop then you would not call it induction.

 

[Andrew Mason]

I have recently found a circuit schematic that can pick up radio signals without the need of a battery.

Is this an example of electromagnetic induction? If so, how much voltage/current is induced?

Does it change the properties of the electromagnetic wave, e.g. energy, wavelength, etc?

Sounds like a crystal radio receiver.

The way the radio wave interacts with an antenna depends on the design of the antenna. The time dependent magnetic field component of the radio wave can induce a current in the antenna. Or the time dependent electric field component of the radio wave can cause current oscillations in the antenna.

Antennas can be complicated. You would need to know particular details of the antenna, and the radio signal to determine the strength of the signal in the antenna and how it interacts with the radio wave.

AM

 

[mavc]

Thank you both for your replies.

In the project details, it says that the antenna is just a really long wire. Do you have further details on the amount of voltage & current generated in the crystal radio receiver?

I forgot the second half of my question - is it possible to induce a current in a coil via a stream of charged particles (i.e. electrons or protons) traveling in a straight line through the coil?

Regards,
Anna.

 

[Andrew Mason]

Thank you both for your replies.

In the project details, it says that the antenna is just a really long wire. Do you have further details on the amount of voltage & current generated in the crystal radio receiver?

It depends on the strength of the radio signal and the gain of the antenna and other technical details. It will be measured in microamperes.

I forgot the second half of my question - is it possible to induce a current in a coil via a stream of charged particles (i.e. electrons or protons) traveling in a straight line through the coil?

No. A steady current creates a steady magnetic field. You need a time dependent magnetic field to create an induced emf (Faraday's law: $\text{Emf} = d\phi/dt$

AM

 

[mavc]

Hi AM,

Thanks for the info on induction in an antenna.

With the moving stream of particles, what if the charge density was changing/oscillating over time? Would that induce a voltage/current?

Thanks,
Anna.

 

[Gordianus]

Say you send a bunch of charged particles trough a coil. Such a bunch would generate a varying magnetic field, thus there would be an induced emf.

 

[mavc]

Thanks Gordianus.

If I need the charged particles to go in a straight line, what other options do I have to be able to induce an emf?

And is there an equation predicting how much voltage/current will be induced?

Regards,
Anna.

 

[Andrew Mason]

Thanks Gordianus.

If I need the charged particles to go in a straight line, what other options do I have to be able to induce an emf?

If you vary the number of charged particles per unit time or if you vary the speed of the charged particles the current will not be constant. You need a time dependent current to create a time dependent magnetic field, which will then create an induced emf.

And is there an equation predicting how much voltage/current will be induced?

The induced emf is determined by Faraday's law. The induced current depends on the circuit (eg. resistance) you are using.

AM

 

[mavc]

Thanks AM.

Going back to the question about electromagnetic induction, is it limited to radio waves or can other frequencies like IR, visible light, x-rays and gamma rays induce a current?

Regards,
Anna.

 

[mavc]

Hi again,

If the current induced from electromagnetic waves is in the order of microamperes, how did Tesla light up few hundred watts of light bulbs kilometres away?

Thanks,
Anna.

 

[Andrew Mason]

Thanks AM.

Going back to the question about electromagnetic induction, is it limited to radio waves or can other frequencies like IR, visible light, x-rays and gamma rays induce a current?

For very small wavelengths, quantum effects become important. Some light as well as Xrays and gamma rays interact with individual particles (e.g. atoms, electrons) and classical electrodynamics (of which induction is a part) starts to break down.

AM

 

[Andrew Mason]

Hi again,

If the current induced from electromagnetic waves is in the order of microamperes, how did Tesla light up few hundred watts of light bulbs kilometres away?

He must have used an enormous amount of power.

AM

 

[mavc]

For very small wavelengths, quantum effects become important. Some light as well as Xrays and gamma rays interact with individual particles (e.g. atoms, electrons) and classical electrodynamics (of which induction is a part) starts to break down.

AM

Then how does induction work? I would have thought that the explanation would be at a quantum level too, in terms of photons interacting with electrons?

Regards,
Anna.

 

[Quinzio]

Hi again,

If the current induced from electromagnetic waves is in the order of microamperes, how did Tesla light up few hundred watts of light bulbs kilometres away?

Thanks,
Anna.

Fortunately, the outcome of Tesla’s tests were more of an inconvenience than a cataclysmic world-ending event. Well, depending on your perspective anyway. The area around his experiement became electrified, but not enough to kill anyone, and there were some very impressive bolts of man-made lightning which stopped when he blew up the town’s generator and caused a blackout over several miles. There might have been one other small side effect. At almost exactly the same time that this experiment was taking place, a mysterious explosion rocked a remote section of Siberia, to the tune of about a 15-megaton blast (40 years before the first Atomic Bomb test).

 

[mavc]

AM, thinking about it a little more, is it possible that induction works on groups of atoms rather than atoms themselves, in the same way that diffraction needs planes of atoms to work?

Quinzio, that's an interesting story. How did he electrify the area around him? Is it related to the Earth's resonant frequencies, or is it to do with wireless em induction?

Thanks,
Anna.