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Homework Help: How does an oscillator truly work?

  1. Jun 12, 2016 #1
    1. The problem statement, all variables and given/known data
    what type of wave is light and how is light propagated through space? How are these types of waves created, for example, with an oscillator.

    2. Relevant equations
    3. The attempt at a solution

    I have the answer sheet because this is a practice test question. but I don't want to be a machine spitting out what i read and I dont want to blank in the exam. a clear understanding would help me through my future studies I am sure. I understand for this question the answer is that "light is an electromagnetic wave and it is made of an electric field and a perpendicular magnetic field that propagate each other through space." but that just sounds very confusing.
    I understand that using an oscillator you have the magnetic force from the inductor and the electric force from the capacitor that propagate each other. Maybe the first question was worded weird because the answer seems to be specific what type of light wave is and how it is propagated through the oscillator.
    For the third question i did quite a lot of research into oscillators and capacitors and inductors reading howstuffworks but still could not understand one main thing. follow this train of thought from howstuff works:
    "If you charge up the capacitor with a battery and then insert the inductor into the circuit, here's what will happen:

    • The capacitor will start to discharge through the inductor. As it does, the inductor will create a magnetic field.
    • Once the capacitor discharges, the inductor will try to keep the current in the circuit moving, so it will charge up the other plate of the capacitor.
    • Once the inductor's field collapses, the capacitor has been recharged (but with the opposite polarity), so it discharges again through the inductor."
    what does the bold part mean?????????? I am so confused as to why that would ever happen.
    how and why does the polarity switch? why doe the inductor charge the other plate of the capacitor. aside from this it mostly makes sense to me.
  2. jcsd
  3. Jun 12, 2016 #2

    Simon Bridge

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    You have the answers so you know - often you are expected to say it is a transverse travelling wave as well though.

    The first question is a compound one - it asks what light is and how it propagates through space. The second asks a completely different question about how a light wave gets generated at the source. You are not asked about propagation of light through the oscillator.

    Unless you have an example in your notes (likely) then think about how a radio antenna works... when used to broadcast.

    Your problem statement only has two questions (count the question marks.)
    Perhaps rewrite the statement, numbering the questions you are answering would be a useful focussing exercise?

    It means what it says ... the inductor wants the current to keep moving. This is a consequence of magnetic induction laws.

    The result is that the inductor is actively forcing charges to move from one plate to the other in the direction they'd normally go ... so if you imagine the cap is initially charged so plat A is positive and plate B is negative, and positive charge is being moved from plate A to plate B, and the inductor is actively shovelling extra charges from plate A to plate B... what happens to the sign of the net charge on plate B and plate A?

    However - neither question asks you how an oscillator works. You do not need to know this to answer the question.
  4. Jun 13, 2016 #3
    I believe the first question asks how electromagnetic waves propagate through space. Not just light but all electromagnetic waves. Im just not satisfied with the answer from the answer key. Seems vague to me.
    I spoke with a friend who does Electrical eng. I did not realize that the charges are moving from one plate through the other through the circuit rather than through the dielectric insulator in the middle. haha
    The sign of net charge flips correct? and then the capacitor discharges again and the inductor will push it back to plate A thats where we get our oscillating wave of voltage.
  5. Jun 13, 2016 #4
    I'm sure you're already aware but an electronic oscillator (using an LC tank circuit) cannot operate at a high enough frequency to generate light waves.
  6. Jun 15, 2016 #5
    no I didn't know. my knowledge of electronics is very limited
  7. Jun 15, 2016 #6

    Simon Bridge

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    ... in physics: all electromagnetic waves are light.
    LC-tank circuits are often used to tune RF transmitters... radio frequency is a kind of light.
    However, it is common for people to reserve the label "light" to the visible and nearby frequencies IR and UV.

    In the context of this problem, radio is light.

    That's close enough.
  8. Jun 30, 2016 #7
  9. Jul 1, 2016 #8

    Simon Bridge

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    No worries.
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