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!

Homewrk: electrical

  1. Nov 6, 2006 #1
    a cable with total resistance of 2 ohms used to transfer 15000W of electrical power with electrical potential of 10000 V.
    How much electrical energy is lose in the cable after transferring 2 hours of electrical power?


    ------------this is how my teacher taught me, but still confused----------
    P = VI
    15000 = 10000 I
    I = 1.5 A

    V = IR
    V = 1.5 * 2
    V = 3

    E = VIt
    E = 3 * 1.5 * (2 * 60 * 60)
    E = 32400 J
    -----------------------------------------------------------------------

    What i don't understand is, since the question has provided me with 10000V, why should i find another voltage (1.5V)? It's impossible for a cable to have 2 completely different voltage (1.5V and 10000V) is it?
    My question is, what is 1.5V and 10000V?:yuck:
    Why cant i just use,
    E = Pt
    E = 15000 * (2 * 60 * 60)?

    HELP!!!!!!!!!!!!!!!!!! I know my English is not good enough... sorry for that.
     
  2. jcsd
  3. Nov 6, 2006 #2

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The "1.5" is not a voltage, it is a current. 1.5 amperes (1.5 A) means that 1.5 coulombs of charge pass by a given point in the wire every second.

    You cannot use power alone to find transmission loss, because transmission loss depends only on current, not on power. If you use a higher voltage to transmit the same power, you will have smaller transmission losses.

    - Warren
     
  4. Nov 6, 2006 #3
    i'm sorry, erm... not 1.5, it's the 3V actually...(i'm confused!!)
    what is the voltage of 3 and 10000

    The question told me the voltage is 10000, y still need to use formula, V = IR to find the V which is 3V?

    What is the differences between the value of voltage provided by the question and the voltage get from the V = IR?

    My physic is terrible huh??...
     
    Last edited: Nov 6, 2006
  5. Nov 6, 2006 #4

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The cable loses 3V over it's length. At one end, the voltage is 10,000V; at the other it's 9,997V.

    - Warren
     
  6. Nov 8, 2006 #5
    o... now I get it! thanks for your help...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Homewrk: electrical
  1. Electrical circuits (Replies: 2)

  2. Electrical Circuits (Replies: 1)

  3. Electric Discreption (Replies: 1)

  4. Electric Field (Replies: 1)

Loading...