calculate Resistance of a # 10 copper wire

Discussion in 'Homework Help' started by marchen91979, Sep 20, 2010.

  1. marchen91979

    Thread Starter New Member

    Sep 20, 2010
    2
    0
    Please help me to solve five of the questions that I miss on the electronics technician test. Thanks in advance.
    Marvin

    1) What is the resistance of a 1000ft of # 10 copper wire without using the AWG chart. rho is given of 10.370 ohm?


    2) Which of the following wire will safely carry the most current?
    0, 10, 30, 40, -10

    Is wire #0 or #10? Since I don't see the value of the current on the chart, I hesitage to choose wire#0 even I acknowdge that the smaller the wire size the higher the current. (I chose wire #10) AWG #10 has 14.8A which is the highest current among the numbers 30, 40 on the chart.


    3) The resistor of 10Ω has a current equal 1/10A, choose the smallest composition resistor rating:
    1/4w, 1/2w, 1w, 2w, None.

    Is the answer None? because the lowest power rating is calculated by P = I^2 x R
    P= (.1)^2 x 10
    = .01 x 10 = .1w


    4) When align RF receiver, which stage is tuned first?
    Mixer, IF, RF, doen't matter.


    5) What is ohm value of a good condenser?
    infinitive
    50000 – 100000 ohms
    50 – 100 ohm
    Zero
    Non of above

    Is the answer infinitive Ω?
     
  2. electronic_noob

    Member

    Jan 15, 2010
    42
    1
    just on number 3...you have computed it to be 0.1 watt

    I'm no expert but is there a resistor with such rating 0.1 watt, which you can buy?

    maybe the question is hoping for a practical answer...I mean if you need such rating 0.1 watt in real life what would be the rating of the resistor that you think you will end up buying

    I'm no expert,
     
  3. tom66

    Senior Member

    May 9, 2009
    2,613
    213
    I assume they mean capacitor. Condensor is an old term for a capacitor. In which case, none of the above, since an ideal capacitor has no "resistance", like an LED or a diode. When testing with a resistance meter: A capacitor will start with zero ohms and rise to infinity. If the capacitor is leaky, like all capacitors, it will start at zero ohms, and go to the leakage resistance. And, if there is any ESR, then it will start at said ESR and go to the leakage resistance.
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    This doesn't make much sense. The stated rho looks very strange for copper - and the unit is incorrect.

    Unless you know the diameter of #10 AWG wire off the top of your head you are stuck. A rough estimate is that about 10 wires of this diameter lying side-by-side span about 1 inch - but that's very rough. AWG #10 gauge is actually 2.58826mm diameter or about 0.1019".

    If you knew that 4/0 is 0.46" and the successive gauge scale factor is 0.890526 then you are not in need of the chart - good luck on remembering that!

    Maybe you should check the question wording.
     
  5. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    This is a tricky question because it contains a flaw in it. If rho is the given, it is in mhos, not ohms. I'll assume mhos was meant, then the resistance is 1/10.37)=0.96 ohms per foot. (I am assuming per foot, but it was not so stated). The 1000ft * .96ohms/ft = 96 ohms.


    I've never heard of -10 wire. But the largest diameter of the other wires is 0 AWG and therefore it will carry the most current among them.

    Answered above.


    You correctly calculated the power consumed by the resistor to be .1 Watt. Therefore the smallest resistor value listed will be 1/4 Watt since it can handle this power (.25 Watts is greater than .1 Watt). Resistors come in these standard sizes with regard to power. There is no .1 W resistor.

    Just answered.


    Answer: the rf stage is tuned first in a receiver since it is at the front end (closest to the antenna). You adjust it's tuned circuit for maximum signal then the mixer, then the IF stages. Think about it: The IF is last in line as far as tuned circuits in a receiver goes.


    An ideal condenser has infinite resistance and thus blocks dc current.
     
    Last edited: Sep 21, 2010
  6. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Hi PRS,

    On the #10 gauge wire resistance question you wrote ..

    I agree the question is nonsensical.

    The Standard Handbook for Electrical Engineers tabulates the DC resistance per 1000' for various copper temper grades & gauges.

    For #10 gauge copper the resistance per 1000' is stated as follows...

    Hard temper - 1.06Ω

    Medium temper - 1.054Ω

    Soft temper - 1.019Ω

    96Ω is not correct.
     
  7. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    Well hello there, tnk! Here's the quote from the guy who set up this problem:

    "1) What is the resistance of a 1000ft of # 10 copper wire without using the AWG chart. rho is given of 10.370 ohm?"

    And that restriction hereby inhibited looking up the actual numbers while at the same time giving the answer to those who used the information.

    I'm sure you're right! :)
     
  8. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Hi again PRS,

    Yes it's the poorly annotated question from the OP.

    In fact the 10.371 figure gives the volume resistivity of copper in Ω-cmil/ft. So the question still cannot be answered in the absence of the diameter corresponding to #10 gauge value. If you didn't know what #10 AWG corresponds to, then you're stuck.
     
  9. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    LOL! Thanks tnk! ;)
     
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