1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Help with this confusing circuit test tmrw! Find i across resistor.

  1. Feb 20, 2013 #1
    Help with this confusing circuit!! test tmrw! Find i across resistor.


    my teacher lectures to fast and i dont understand the notes i put down. can someone explain this one to me please??
  2. jcsd
  3. Feb 20, 2013 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Re: Help with this confusing circuit!! test tmrw! Find i across resist

    This is the way I would approach the problem...

    You can ignore the 12 Ohm resistor because it's across the 240V supply and has no effect on the current or voltage in the rest of the circuit.

    To find the current in the 40 Ohm I would first aim to work out the voltage across it.

    I note that the 60, 40 and 48 Ohm are in parallel and that 60//40//48 works out as ...

    1/(1/60 + 1/40 + 1/48) = 16 Ohm

    Then I note that the 8 Ohm and 16 Ohm form a voltage (aka potential) divider...


    So the required voltage across the 40 Ohm is...

    240 * 16/(8+16) = 160V

    Therefore the current through the 40 Ohm is

    I40 = 160/40 = 4A
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook