Answers should be: 1A upward for the 200 ohm resistor, 4A upward for the 70 ohm

Question

Answers should be: 1A upward for the 200 ohm resistor, 4A upward for the 70 ohm one, 8A downward for the 20 ohm one, and 3A upward for the 80 ohm one, Please help I just cant do these kirchoff problems

In each case, suppress units for clarity and simplify, combining the terms. (d) Solve the junction equation for I3 (C) Using the equation found in part (d), eliminate I3 from the equation found in part (b), (f) Solve the equations found in parts (a) and (e) simultaneously for the two unknowns I3 and I2 (g) Substitute the answers found in part (f) into the junction equation found in part (d), solving for I3. (h) What is the significance of the negative answer for I2? W In the circuit of Figure P2151, determine (a) the current in each resistor and (b) the potential difference across the 200-ohms resistor.

Explanation / Answer

call all currents going up positive
then junction equation I1 + I2 + I3 + I4 = 0

left loop

-80 I2 + 40 + 200 I1 = 0

I2 = (40 + 200 I1)/80

slight larger loop going through middle

-20 I3 -360 + 200 I1 = 0

I3 = (-360 + 200 I1)/20

now full loop
-70 I4 + 80 +200 I1 = 0

I4 = (80 + 200 I1)/70

plug into first equation

I1 + (40 + 200 I1)/80 + (-360 + 200 I1)/20 + (80 + 200 I1)/70 =0

I1 = 1 A, positive so up

now plug into I2 equation
I2 = 240/80 = 3A

I3 = -160/20 = -8 A (- means downard)

I4 = 280/70 = 4A

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