Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.

lod asked in Science & MathematicsPhysics · 3 years ago

Physics Question - Current in Resistor of parallel circuit - Need Help!?

Cannot see why it isn't 0.65. I worked out that the current for both parallel circuit and the 9 Ohm resistor is 0.75. So 32/37*0.75 =0.65 but it says it's incorrect. The hints don't help at all, so I was hoping someone could help me? Thank you

Attachment image

4 Answers

Relevance
  • 3 years ago
    Favorite Answer

    The three R's in parallel are equivalent to

    1/R = 1/5 + 1/12 + 1/20

    1/R = 0.2 + 0.083 + 0.05 = 0.333

    R = 3 Ω

    add 9 in series to get 12 Ω

    I = e/R = 9/12 = 0.75 amp

    that produces a voltage across the 3 in parallel of

    E = IR = 0.75 x 3 = 2.25 volts

    and the currents in the 3 branches are

    I = E/R

    I = 2.25/5 = 0.45 amp

    I = 2.25/12 = 0.1875 amps

    I = 2.25/20 = 0.1125

    (the three should add up to 0.75 amps)

    PS, the circuit is drawn poorly, the junctions have to be shown clearly, see below.

    Attachment image
  • 3 years ago

    The 5 Ω, a 12 Ω, and a 20 Ω resistor are in parallel with each other.

    1/Req = 1/5 + 1/12 + 1/20 = ⅓

    Req = 3 Ω

    Total resistance = 9 + 3 = 12 Ω

    B. I = 9 ÷ 12 = 0.75 amps

    Let’s use the following equation to determine the voltage for the 9 Ω resistor.

    V = I * R = 0.75 * 9 = 6.75 volt

    To determine the voltage for each of the resistors in parallel, subtract this number from 9.

    V = 9 – 6.75 = 2.25 volts

    I 5 = 2.25 ÷ 5 = 0.45 amp

    I 12 = 2.25 ÷ 12 = 0.1875 amp

    I 20 = 2.25 ÷ 20 = 0.1125 amp

    To check these currents, the sum should be 0.75 amps.

    Sum 0.45 + 0.1875 + 0.1125 = 0.75

  • 3 years ago

    The total current is 0.75A as you say.

    The currents in the branches are:

    5R: 0.45A

    12R: 0.1875A

    20R: 0.1125A

    Sanity check: 0.45 + 0.1875 + 0.1125 = 0.75

  • Anonymous
    3 years ago

    Try 1.8 but I’m not sure it’s right

Still have questions? Get your answers by asking now.