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Homework Help: Resistance and current problems

  1. Jan 13, 2004 #1
    Problem 5.
    A total charge of 12mC passes through a cross-sectional area of a nichrome wrie is 3.1s.
    If the number of charges that pass through the cross-sectional area furing the given time interval doubles, what is the resulting current? In units of A.
    Note: What formula(s) should I use?

    Problem 7.
    How long does it take for 7.5 C of charge to pass through a cross-sectional area of a copper wire if I=19A? In units of s.
    Note: I don't know where to start?

    Problem 11.
    A typical color television draws 2.8 A of current when connected across a potential difference of 121V.
    What is the effective resistance of the television set? Answer in omega.
    Note: What formula(s) should I use?
     
  2. jcsd
  3. Jan 13, 2004 #2
    Current can be defined as the charge which passes a given point in one second. Specifically, 1 ampere of current is 1 coulomb of charge passing a given point in one second.

    If you have 12 milli-coulombs pass in 3.1 seconds then it's a simple matter to calculate how many coulombs are passing in 1 second. That would be the current in amperes. Current (in amperes) equals Charge (in Coulombs) divided by time (in seconds). I=C/T

    If charge doubles, then it's easy to see what happens to current by looking at the formula. Current is directly proportional to charge.

    --

    Here we are given 19 amperes of current and are asked to find the time it takes 7.5 coulombs of charge to pass a given point. First ask yourself how many coulombs are passing a given point in one second. If we have 19 amperes of current, we have 19 coulombs of charge passing any given point in one second. If it takes 1 second for 19 coulombs of charge to pass, how long will it take for 7.5C of charge to pass?

    --

    Simple ohms law problem:

    Voltage(V)= Current(I) * Resistance(R)

    To find resistance, R=E/I.
     
    Last edited: Jan 13, 2004
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