1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Understanding Ohm's Law

  1. Nov 2, 2013 #1
    I am confused and need advice in applying Ohm's Law (V=IR) to certain problems. The Math is okay, but the concept is what getting me confused.

    Question 1:There's a scenario:Current is passing through a resistor.

    (a) I am assuming current is being converted to heat as it passes through. Correct? Due to conversation of charges?

    (b) Ohm's law also states that Resistance is the same.So I am understanding that, for this scenario, resistance stays the same.Therefore, for V=IR, if current is decreasing (being converted to heat), would that mean Voltage is Increasing to make for this loss? To compensate the fact that Resistance stays the same?

    That part is tricking me up

    Question 2: The next question applies to the following Image
    http://i.imgur.com/iqRVxew.jpg?1

    Find the resistance between the following

    (c)~A and B
    (d)~E and D
    (e)~D and C (give your reasoning)
    (f)~C and B
    (g)~A and E

    My attempt

    Well, I feel like this is a trick question.

    (c) 2 ohms; Well, it is directly connected
    (d) 3 ohms
    (e) 10 ohms; Once again, it is directly connected. But I am pretty sure my teacher won't accept that reasoning
    (f) This: I completely do not know. It can go any of the three routes: 6, 12,4 Ohms.
    (g) No clue.

    Question 3 Why do the terminals of a battery have to be connected together before current flows?

    My reasoning: Since a battery produces an electrical pressure, the charges build up on one end of the terminal. Therefore, it needs a path to go to the oppositely charged end. This, in turn, would then produce a current.

    Is that right?

    Question 4 This pertains to the following image.

    http://i.imgur.com/IhayTqp.jpg

    Scenario: There is an excess positive charge at the "High Potential Region" The left end of the wire is held at a negative potential. Draw the arrows on the following diagram to show where the positive charges go.

    my attempt

    I am assuming this means draw the current. Is my work correct?

    http://i.imgur.com/mfryuuv.jpg

    Question 5

    Draw the arrows besides the resistors to denote the direction of conventional current through the resistors. Also, Explain why the arrows point in the way that you have drawn

    http://i.imgur.com/SXza0sE.jpg

    Attempt I think this was Easy but I cannot be so sure. :] The arrows point that way is because by convention, the current is drawn from a voltage drop.

    My reasoning, I am not so sure.

    http://i.imgur.com/JHyhgwd.jpg

    Thanks for the help in advance. I hope the pictures weren't too blurry. Not everyone can afford an iphone Xd
     
  2. jcsd
  3. Nov 2, 2013 #2

    mukundpa

    User Avatar
    Homework Helper

    Please go through the text thoroughly.

    Electric charge is conserved. the charge is only circulating through the circuit and the battery. Battery supplies energy to the charge to flow through the circuit against resistance and that energy supplied by the battery is converting to the heat energy in the resistance.
     
  4. Nov 3, 2013 #3

    NascentOxygen

    User Avatar

    Staff: Mentor

    Your arrows are correct. Current flows from a point of higher potential to a point of lower potential.

    Not so much a trick question as testing whether you can analyze an unfamiliar circuit calmly and methodically.
    (c) and (d) are correct.

    In (e) I can see 2 parallel paths that current can take to get from D to C. You seem to have considered only one path.

    In (f), there are a number of parallel independent paths for current to take. What is the formula for the equivalent resistance of resistances in parallel?
     
  5. Nov 3, 2013 #4
    For Parallel, 1/R(total)=1/R(1)+1/R(2)

    I think I know where you want me to go to. Thanks!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Understanding Ohm's Law
  1. Ohm law (Replies: 2)

  2. Ohm's Law and power (Replies: 1)

  3. Ohm's Law (Replies: 4)

  4. Ohms law (Replies: 1)

  5. Ohm's law (Replies: 3)

Loading...