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how to identify component from graph

Discussion in 'Homework Help' started by Parth86, Jul 27, 2016.

  1. Parth86

    Parth86 Member

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    How to identify the component
    IMG_20160727_123248.jpg
    I think, it is not resistor because it does not follow the condition. If the voltage is increase the current should be decrease
     
  2. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    V=Ldi/dt

    L=?
     
  3. Parth86

    Parth86 Member

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    How do you know that it is a inductor? Can you tell me why it is not capacitor?
     
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  4. dave

    Dave New Member

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  5. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    because di/dt is a constant with V=constant

    So how much is L?
     
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  6. Parth86

    Parth86 Member

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    OK voltage across the inductor will be zero if the current throw it remains constant
    di/dt=0.2*1000 A/sec
    Voltage=2v
    Then L=10 mH
     
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  7. spec

    spec Well-Known Member Most Helpful Member

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    A couple of handy formulas that crop up frequently are:

    (1) Q = C * V= I * T
    and
    (2) Q = L * I =V * T

    Where:
    Q = Charge in Columbs
    C= Capacitance in Farads
    L= Inductance in Henries
    V = Voltage in Volts
    I = Current in Amps
    T = Time in seconds

    spec
     
  8. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Another interesting side point is that if the voltage is really forced down to zero at t=5ms as in the drawing, then the current would stay constant at 1 amp forever given an ideal inductor. It would really have to be ideal too, with no series resistance and no other losses or else the current would die down over time.
    We can get this from:
    V=L*di/dt
    di/dt=V/L
    and with V=0 we have:
    di/dt=0/L=0 amps/second
    so the current can not change because the current was already 1 amp and the rate of change of current is zero.

    Another rationale for this is the inductor is the dual of the capacitor, and the ideal capacitor holds a constant voltage with an open circuit so the inductor holds a constant current with a short across it (and current is the dual of voltage and a short circuit is the dual of an open circuit).

    Of course a real life inductor would not do this because there would be some kind of loss which would cause the current to die down toward zero over time. It may be possible though with a super conducting device.
     
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  9. spec

    spec Well-Known Member Most Helpful Member

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    Hi MrAl,

    Yes, once you realise that capacitance is the compliment of inductance, electronics becomes a bit clearer.

    A handy acronym is CIVIL which stands for, 'with a capacitor the current leads the voltage (by 90 degrees) and with an inductor voltage leads current (by 90 degrees)'.

    As the voltage and current are 90 degrees out of phase a perfect capacitor and a perfect inductor can never dissipate any power.

    It is hard to believe that most non-volatile memory (flash) relies on a minute charge on an impossibly small capacitor in the femto Farad range, to store a digital state (zero or one) for a period of up to 50 years.

    Another pair of handy formulas are:

    (1) Energy stored in a capacitor is, (C * V * V)/2
    and
    (2) Energy stored in an inductor is, (L * I * I)/2
    Where
    energy is in Joules
    C = capacitance in Farads
    L = inductance in Henrys
    V = Voltage in Volts
    I = Current in Amps

    And finally two rules:

    (1) you can never put a voltage across a perfect capacitor (or an infinite current will flow)
    and
    (2) you can never force a current through an inductor (or an infinite voltage will be generated)

    spec
     
    Last edited: Jul 31, 2016
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  10. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi there spec,

    Yes some good points which are always good to think about when dealing with capacitors and inductors, like zero power.

    Yeah it is interesting how the very small memory elements can hold a charge for so long...i think there is some sort of small positive feedback involved too. Have to read up on it again i guess.
    Then there is the more recent ferroelectric memory, which also must have very small 'capacitors' in there.
    Things have changed quite a bit since the 70's when we had to use IR erasable EPROMs where we were lucky to have 2k bytes of storage.
     
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  11. spec

    spec Well-Known Member Most Helpful Member

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    DRAM (all large memory) also relies on a minute capacitor to store charge, but only for a few miliseconds before the charge is refreshed.

    And before EPROM there was PROM where you blasted links. Although rudimentary by modern standards, PROMs were a game changer when they first came out.:cool:

    Yes, ferroelectric; I had forgotten about that.

    spec
     
    Last edited: Jul 31, 2016
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  12. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again,

    Yeah i remember those days well. And the Z80 and dram, i used static memory instead i cant remember why, i think because i wanted to use battery backup without having the processor running.

    Do you remember the old magnetic core memories? I actually worked with terminals that had these as their only non volatile memory. The memory core looked like a little brain on a big PC board with many transistors and IC's and stuff. It was cool. The large board only held maybe 400 bits or something, but cant remember the exact number now. It was a square matrix of tiny tiny toroid cores with wires running through the center of each one forming rows and colums. It was really cool, wish i had one of those boards again just to marvel at really :)
    When i think back, geeze, a board maybe 12 inches by 18 inches or something and it was able to store less than 1k. Now we have SMD parts that are smaller than a thumbnail and can store gigabytes. What a change from the 1970's.
     
  13. spec

    spec Well-Known Member Most Helpful Member

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    :) Those were the days. You had to work really hard to realise a function. It was a constant tug between size, power consumption, and cost.

    Hardware magazines were full of circuits to minimize the number of components and software magazines described software to minimize lines of code, but now, with the fantastic progress in electronics and computing the sky is the limit.

    Those core-store boards, as you say, were a work of art. I used to get them from the states to strip for parts, but just junked the core matrix.

    I worked on an Army mortar locating equipment which was full of 709 opamps, servo motors, gears, transformers, and precision AC potentiometers. The readout was on two counters, like the milometers on older automobiles. The equipment was also a work of art and you could see it working. Nowadays you could do the whole thing, and better, with an Arduino Due or two and an lCD display.

    The progress in electronics has had a downside though; some surface mount parts are so small that they are not suitable for hobbyists and systems are so complex that often they cannot be repaired.:arghh:

    spec
     
  14. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    I remember during one of my many visits to the Smithsonian museum in DC (mid-80's). I was wandering around in the computer section and spied an unidentified device.

    It was an approximately 4"X6"X2" block of aluminum with an odd looking PCB mounted on its top.

    I asked a docent what it was. He responded that it was an experimental, 2k memory "brick" from IBM.

    It had two small port tubes in the Al block and I asked if he knew their purpose. He said they were for the liquid nitrogen used to cool the "brick"... :cool:.
     
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  15. spec

    spec Well-Known Member Most Helpful Member

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    Sounds like super conduction would be involved somewhere.

    I would love to visit the Smithsonian.:cool:

    spec
     
  16. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Drifting off-topic, but...
    It's pretty neat, for sure. The "new" Udvar-Hazy (Smithsonian National Air and Space Museum's annex at Washington Dulles International Airport) is also remarkable. It has a whole section devoted to diesel aircraft engines - none of which were ever actually used in an aircraft :banghead:.

    Plus an SST, front portion of a Space Shuttle, the Enola Gay (of BIG bang fame), etc..

    Visited the Science Museum in London a few years back. The whole first floor was devoted to steam. Actual working models of dozens of designs. Very, very cool.

    Back on-topic:
    Did not know this acronym. Thanks, spec.
     
  17. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Funny you should mention the SST, as they are trying to bring one back from the dead and might have the money to do it. Question is can they keep it maintained.
     
  18. throbscottle

    throbscottle Well-Known Member

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    What's an SST?
     
  19. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    SuperSonic Transport usually aircraft like the Concorde.
     

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