LC Circuit

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sciencee33
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LC Circuit

Post by sciencee33 »

Hi!

I am having trouble understanding how an LC circuit works. Can someone please explain this to me? All I know is that it uses electrical energy to output frequency, but the frequency output decreases over time. Is there a way to prevent the amount of output frequency from being decreased?

Thank you!
Brindha
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Re: LC Circuit

Post by bfinio »

Hi - this forum is for K-12 students who need help with science fair projects. Are you working on a science project that involves LC circuits, and if so, can you provide us with more details? If this is a general/homework-related question, there are other forums online that are better suited to your question. You can also find many circuit tutorials on YouTube if you search.

Thanks,

Ben
sciencee33
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Re: LC Circuit

Post by sciencee33 »

Hi!

Yes, I am working on a science project that involves LC circuits. I am trying to use an LC oscillator to release different frequencies for something else I am experimenting, but I am very confused as to how they actually work. I've tried looking at articles and YouTube videos, but I am still stuck. Would you be able to explain to me how LC oscillators work?

Thank you!
Brindha
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Re: LC Circuit

Post by bfinio »

Hi - so, this is a pretty advanced topic that is usually taught in a college-level circuits class. It is hard to jump into explaining how an LC oscillator works without knowing more about your background in circuits. Have you taken a physics class where you learned about topics like voltage, current, resistance, and Ohm's Law? If so, did you also learn about capacitors and inductors? Once I know more about your background, I can try to provide a more appropriate explanation.
sciencee33
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Re: LC Circuit

Post by sciencee33 »

Hi!

I am currently taking an AP Physics class right now, but I am well acquainted with terms like voltage, current, resistance, and Ohm's Law, but I am not familiar with capacitors and inductors.

If it helps here is a brief overview of my project:
Cell phones release a harmful amount of electromagnetic radiation with high frequencies. Subatomic particles in human bodies, or in any matter, tend to vibrate at the frequency of their surroundings. When humans are exposed to the higher frequency range emitted from cell phones, their vibrations become wild and imbalanced. I am trying to develop a technology that will constantly release an electromagnetic field with a lower, healthier frequency. This way, our bodies can resonate with this healthier frequency, thus counteracting the vibrational imbalance. And for my project, I think that an LC circuit could be useful in producing a specific frequency.
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Re: LC Circuit

Post by bfinio »

Hi - are you able to ask your physics teacher for any help understanding capacitors, inductors, and LC circuits? This is a pretty advanced topic, and it's going to be difficult to give you a complete understanding in an online forum like this.

However, I can give my best shot at a mechanical analogy. I teach an electronics class at Cornell and this approach usually helps students. A mechanical system like a spring has a resonant frequency that depends on its mass and stiffness. Imagine holding a slinky vertically by one end, and letting the free end bounce up and down. It will oscillate at the system's natural, or resonant, frequency. If you hang a heavy mass from the end of the spring, the resonant frequency will go down. If you use a stiffer spring, the resonant frequency will go up. As the spring oscillates, the energy in the system also oscillates back and forth between kinetic energy of the moving mass and potential energy of the stretched spring. Since there is always some friction, eventually this energy dissipates (in the form of heat) and the oscillations gradually get smaller and smaller until the spring stops moving.

LC circuits work the same way, but with electricity instead of physical motion. The capacitor and inductor can both store energy in different ways. Energy oscillates back and forth between the two circuit components, just like energy oscillates back and forth between the stretched spring and the moving mass. Since there is always some resistance in a circuit, eventually the energy will dissipate (again in the form of heat) and the oscillations will stop. The resonant frequency of the LC circuit depends on the inductance and capacitance - you can look up the formula, and you will see that if you increase either inductance or capacitance, the resonant frequency will go down.

I saw your other thread about cell phones - my word of warning here is that there is a lot of pseudoscience in the area of the human body and vibrations (think "healing crystals," various devices you can buy that claim they will improve your health because they are in tune with your body's natural vibrations, etc). This isn't my area of expertise, but be careful and make sure all of your research is from reputable sources or peer-reviewed publications. Avoid personal blogs and websites that aren't from an institution like a government agency, professional society, or university. There is a LOT of bad, misleading, and outright false information on the internet.

Good luck with your project!
sciencee33
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Re: LC Circuit

Post by sciencee33 »

Hi!

Thank you so much for your explanation of LC circuits, I think I really understand it now. I looked into what you said about energy dissipating as it oscillates back and forth between the inductor and capacitor, and I designed an LC circuit with a feedback loop (attached below) in order to ensure that the oscillations do not die out.

I am just confused as to how I am supposed to connect the oscilloscope meter (labeled as XSC1) to the circuit. In other words, I don't know which terminals I am supposed to connect and where on the circuit I should connect them. If you could help me with this, I would really appreciate it.

Also, if I were to connect multiple of these lc circuits with feedback loops together in parallel, would that increase the intensity of the electromagnetic wave released. Would this increase the frequency of the wave?

For reference, I designed my circuit on EasyEDA, a free circuit simulating website.

Thank you so much!
Brindha
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lc with feedback.pdf
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bfinio
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Re: LC Circuit

Post by bfinio »

So, unfortunately this project is getting a little too advanced for our forums. I am a mechanical engineer by training and I teach a mechatronics class for mechanical engineers. We cover basic RC, LC, and RLC circuits but not more advanced circuits with feedback like the one you posted. You might have more luck on an electronics-specific forum like https://electronics.stackexchange.com/.

I can tell you that for the oscilloscope, you could connect the - terminal of one of the measurement channels (A or B) to ground in your circuit, and the + terminal to the point where you want to measure the voltage. We don't have our own oscilloscope tutorial but there should be plenty on YouTube.

Hope that helps!
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