# What are the Unknown EMF and Currents in this Kirchhoff's Circuit?

• Bob Loblaw
In summary, the conversation discusses finding the unknown emf and currents in a circuit using Kirchhoff's circuit laws. The equations and attempts at a solution are also provided. However, there is a mistake in the attempt which leads to an incorrect answer. The conversation ends with a question asking for help in identifying the mistake.
Bob Loblaw

## Homework Statement

http://img207.imageshack.us/img207/1685/p1854altco4.gif

Find the unknown emf and the unknown currents in the circuit below, in which R = 3.48 . Take the positive direction for current flow in each branch to be upwards.
EMF = V
left branch= A
right branch= A

## Homework Equations

Kirchhoff's circuit laws

## The Attempt at a Solution

I added current lines to the diagram. Note that a coordinate system is imposed and all positive charges point up ( I guess this makes grading easier). I sketched the lines of current as best I could.

Here are my equations:

Left loop:

1.00v-3.48I1-E+(.05*2)

Outside loop:

1.00v-3.48I1-1.00I3+1.20V+4.00I3=0 (edit: caught a mistake here, last term should have been positive)

Apply junction rule to top center junction:
I1+.05=I3

Combine terms:
1.00v-3.48I1-E+.1=0
2.20v-3.48I1+3.00I3=0

Substituting I1+.05 for I3:

2.20v-3.48I1+3.00I1+.15=0

Combining like terms:

2.35-.48I1=0

I1(the left loop)=4.90A which is wrong.

Any ideas where I messed up?

Last edited by a moderator:
Where is the circuit diagram?

coolram80295 said:
Where is the circuit diagram?

Blast from the past! I have since moved past physics and on to medicine so things worked out well enough I suppose.

## 1. What are Kirchhoff's circuit laws?

Kirchhoff's circuit laws are fundamental rules that govern the behavior of electrical circuits. They were developed by German physicist Gustav Kirchhoff in the 19th century and are used to analyze and solve complex electrical circuits.

## 2. What is Kirchhoff's first law?

Kirchhoff's first law, also known as the Law of Conservation of Charge, states that the total current entering a junction in a circuit must equal the total current leaving the junction. This is based on the principle that charge is neither created nor destroyed in a circuit.

## 3. What is Kirchhoff's second law?

Kirchhoff's second law, also known as the Kirchhoff's Voltage Law (KVL), states that the sum of voltages around any closed loop in a circuit must be equal to the sum of voltage sources. This law is based on the principle of energy conservation.

## 4. How do Kirchhoff's laws help in circuit analysis?

Kirchhoff's laws provide a systematic and mathematical approach to analyze complex circuits. By applying these laws, the current and voltage at any point in a circuit can be calculated, allowing for the prediction of circuit behavior and troubleshooting of any issues.

## 5. Are Kirchhoff's laws applicable to all types of circuits?

Yes, Kirchhoff's laws are applicable to all types of circuits, including DC and AC circuits. However, they do not take into account the effects of capacitance and inductance, which are important in high frequency circuits. In these cases, additional laws and principles are needed for accurate analysis.

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