# FInding current in parallel and series circuits

#### rocky4920

1. Homework Statement 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?

2. Homework Equations
R12 = R1 +R2
R34 =R3 + R4
1/Rt = 1/R12 + 1/R34
I3=I4

3. 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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#### berkeman

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#### berkeman

Mentor
Thanks, but what is the battery voltage? Sorry if I'm missing it...

#### rocky4920

There was no battery voltage given in the problem.

#### CWatters

Homework Helper
Gold Member
You don't need the battery voltage to answer the questions.

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?

• rocky4920 and berkeman

#### rocky4920

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.

#### CWatters

Homework Helper
Gold Member
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.

#### rocky4920

V= IR V= 1.5 (3)
V= 4.5 V for voltage drop for 3 ohm resistor.