sue asked in Science & MathematicsPhysics · 1 month ago

find voltage and currenth?

question 1: What is the voltage at Point A relative to the bottom rail?

question 2: What is the current through R1?

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4 Answers

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  • 1 month ago
    Favorite Answer

    Va=16.678v

    IR1=29.782mA

    The value I is current not currenth.

    Figured with superposition.

    Checked with spice.

  • oubaas
    Lv 7
    1 month ago

    using superposition :

    I3 = 19.7/680-4.6*10^-3*560/680 = 0.025 A run by voltage source

    Va = -I3*R3 = -3.0 V

    I1 = (19.7+Va)/R1 = 16.7/560 = 0.030 A (30 mA)  

  • 1 month ago

    Top of ckt = node V. Apply KCL above R3:

    (V+19.7)/560 + V/120 = 0.0046

    V(1/560+1/120) = 0.0046 - 19.7/560 = -0.030579A = 30.6mA

    -0.030579/(1/560+1/120) = -3.02 <<<<< Q1

    (V+19.7)/560 = (-3.02+19.7)/560 = 29.8mA  left into R1 and then DOWN into 19.7V  source <<<<<< Q2

    Power from sources: (-3+4.6*1.5)*4.6 = 18mW 

    19.7*29.8 = 587mW -----> 587+18 = 0.6W

    Consumed in resistance: 

    0.0298²*560+0.0046²*1500+0.0251²*120 = 0.6W checks

  • 1 month ago

    I'll use superpostion

    1. voltage at A due to voltage source:

    current source is open circuited.

    I = 19.7/(560+120) = 0.0290 amp

    Va = 120 x 0.0290 = 3.48 volts, negative

    2. voltage due to current source. Voltage source is shorted.

    120 parallel with 560 = 120•560/680 = 98.8 Ω

    Va = 98.8 Ω x 4.6 ma = 455 mV, positive

    add the two, Va = –3.48 + 0.455 = –3.02 volts

    voltage across R1 = –19.7 –3.02 = –19.4 v

    I = E/R = 19.4/560 = 0.0346 amp pointed left

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