FInding current in parallel and series circuits

AI Thread Summary
The discussion focuses on calculating net resistance, current, and voltage drop in a circuit with resistors in series and parallel. The net resistance was determined to be 2.5 ohms, with a current of 1.5 A flowing through the 4 Ω resistor. The voltage drop across the 3 Ω resistor was calculated to be 4.5 V. It was clarified that the battery voltage is not necessary for solving the problem, as the same voltage is present across both parallel strings of resistors. The final voltage drop for the 3 Ω resistor was confirmed to be correct at 4.5 V.
rocky4920
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Homework Statement


Mixed Circuits Image.png

a. What is the net resistance in the circuit?
b. What is the current through the 4 Ω resistor?
c. What is the voltage drop across the 3 Ω resistor?

Homework Equations


R12 = R1 +R2
R34 =R3 + R4
1/Rt = 1/R12 + 1/R34
I3=I4

The Attempt at a Solution


a) R12 = 2+ 3
R 12= 5 ohms
R34 = 4+1
R34 = 5 ohms
1/Rt =1/5 + 1/5
1/Rt = 2/5 ohms
Rt/1 = 5/2 ohms
Rt= 2.5 ohms

b) I3 =I4
I3 = 1.5 A

c) For parallel circuits, voltage is the same across. However, with two series made up in the parallel, my formula does not seem to be correct. For instance, to find V4, V =IR... V= 1.5 (1) = 1.5 V
V3 = IR ... V3= 1.5(4) = 6 V. Following this way, the voltage will not be same throughout the circuit. I am asking for some guidance on finding the voltage and solution for part c.
Thank you.
 

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Sorry about that! Image above.
 

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Thanks, but what is the battery voltage? Sorry if I'm missing it...
 
There was no battery voltage given in the problem.
 
You don't need the battery voltage to answer the questions.

Your answers for a and b are correct.

For c... There are two strings of resistors in parallel with the battery. Both strings are 5ohms. They both have the same voltage across them. The current in one is known. So what is the current in the other?
 
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Ok so would the current for R1 R2 be the same for R3 R4 being 1.5 amps? Therefore, making R1, R2, R3, and R4 V= IR V= (5 ohms) (1.5 A) V= 7.5 V at each throughout circuit.
 
The battery voltage must be 7.5V. but check what they asked you for in c.

Yes the current through the string R1 and R2 is same as R3 and R4.
 
  • #10
V= IR V= 1.5 (3)
V= 4.5 V for voltage drop for 3 ohm resistor.
 
  • #11
Correct
 
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