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Analyze the circuit shown in the image, identify the components and their values, and determine the currents I1, I2, and I3.

Physics

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Answer

I1=−0.6AI_1 = -0.6A

I2=−2AI_2 = -2A

I3=−2.6AI_3 = -2.6A

Step-by-step solution

5 steps

To solve this circuit, we will use nodal analysis.

  1. Define nodes and assign a reference node.

    Let the top horizontal line be Node A with potential VAV_A.
    Let the bottom horizontal line be Node B with potential VBV_B.
    We set Node B as the reference node, so VB=0VV_B = 0V.

  2. Apply Kirchhoff's Current Law (KCL) at Node B.

    Based on the current arrows in the diagram:

    • Current I3I_3 enters Node B.
    • Current I1I_1 leaves Node B.
    • Current I2I_2 leaves Node B. Therefore, KCL at Node B states that the sum of currents entering the node equals the sum of currents leaving the node:
    I3=I1+I2(Equation 1)I_3 = I_1 + I_2 \quad (\text{Equation 1})
  3. Express branch currents in terms of node voltages.

    We will write expressions for I1I_1, I2I_2, and I3I_3 using Ohm's Law and considering the voltage sources in each branch. The current direction is from higher potential to lower potential. Since the arrows for I1,I2,I3I_1, I_2, I_3 point from Node A towards Node B (or through components to Node B), we assume VAV_A is higher than VBV_B.

    For the leftmost branch (containing the 2Ω2\Omega resistor, 15V15V source, and 3Ω3\Omega resistor):
    Current I3I_3 flows from Node A, through the 2Ω2\Omega resistor, then through the 15V15V source (positive terminal up, negative down), then through the 3Ω3\Omega resistor, and finally to Node B.
    The voltage drop across the resistors and the source in the direction of I3I_3 is:

    VA−I3(2Ω)−15V−I3(3Ω)=VBV_A - I_3(2\Omega) - 15V - I_3(3\Omega) = V_B

    Since VB=0VV_B = 0V:

    VA−5I3−15=0V_A - 5I_3 - 15 = 0 I3=VA−155(Equation 2)I_3 = \frac{V_A - 15}{5} \quad (\text{Equation 2})

    For the middle branch (containing the 4Ω4\Omega resistor and 10V10V source):
    Current I2I_2 flows from Node A, through the 4Ω4\Omega resistor, then through the 10V10V source (positive terminal up, negative down), and finally to Node B.

    VA−I2(4Ω)−10V=VBV_A - I_2(4\Omega) - 10V = V_B

    Since VB=0VV_B = 0V:

    VA−4I2−10=0V_A - 4I_2 - 10 = 0 I2=VA−104(Equation 3)I_2 = \frac{V_A - 10}{4} \quad (\text{Equation 3})

    For the rightmost branch (containing the 5Ω5\Omega resistor and 5V5V source):
    Current I1I_1 flows from Node A, through the 5Ω5\Omega resistor, then through the 5V5V source (positive terminal up, negative down), and finally to Node B.

    VA−I1(5Ω)−5V=VBV_A - I_1(5\Omega) - 5V = V_B

    Since VB=0VV_B = 0V:

    VA−5I1−5=0V_A - 5I_1 - 5 = 0 I1=VA−55(Equation 4)I_1 = \frac{V_A - 5}{5} \quad (\text{Equation 4})
  4. Substitute into KCL and solve for VAV_A.

    Substitute Equations 2, 3, and 4 into Equation 1:

    VA−155=VA−55+VA−104\frac{V_A - 15}{5} = \frac{V_A - 5}{5} + \frac{V_A - 10}{4}

    To eliminate the denominators, multiply the entire equation by the least common multiple of 5 and 4, which is 20:

    4(VA−15)=4(VA−5)+5(VA−10)4(V_A - 15) = 4(V_A - 5) + 5(V_A - 10) 4VA−60=4VA−20+5VA−504V_A - 60 = 4V_A - 20 + 5V_A - 50 4VA−60=9VA−704V_A - 60 = 9V_A - 70

    Rearrange the terms to solve for VAV_A:

    70−60=9VA−4VA70 - 60 = 9V_A - 4V_A 10=5VA10 = 5V_A VA=105=2VV_A = \frac{10}{5} = 2V
  5. Calculate the currents I1,I2,I3I_1, I_2, I_3.

    Now substitute VA=2VV_A = 2V back into Equations 2, 3, and 4:
    For I3I_3:

    I3=2V−15V5Ω=−13V5Ω=−2.6AI_3 = \frac{2V - 15V}{5\Omega} = \frac{-13V}{5\Omega} = -2.6A

    For I2I_2:

    I2=2V−10V4Ω=−8V4Ω=−2AI_2 = \frac{2V - 10V}{4\Omega} = \frac{-8V}{4\Omega} = -2A

    For I1I_1:

    I1=2V−5V5Ω=−3V5Ω=−0.6AI_1 = \frac{2V - 5V}{5\Omega} = \frac{-3V}{5\Omega} = -0.6A

    The negative signs indicate that the actual direction of current flow is opposite to the direction indicated by the arrows in the diagram.

    The final answers are:

    I1=−0.6AI_1 = \boxed{-0.6A} I2=−2AI_2 = \boxed{-2A} I3=−2.6AI_3 = \boxed{-2.6A}
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