Kirchhoff’s current law
In 1847, G. R. Kirchhoff extended Ohm’s law with two important statements that are referred to as Kirchhoff ’s laws. The first law, known as Kirchhoff’s current law, states the following:
● The algebraic sum of all the currents entering and leaving a junction is equal to 0.
Here is another way of stating Kirchhoff ’s current law:
● The total current flowing into a junction is equal to the sum of the current flowing out of that junction.
A junction is defined as any point of a circuit at which two or more current paths meet. In a parallel circuit, the junction is where the parallel branches of the circuit connect.
In Figure 14-22, point A is one junction and point B is the second junction. Following the current in the circuit, IT flows from the voltage source into the junction at point A. There the current splits among the three branches as shown. Each of the three branch cur- rents (I1, I2, and I3) flows out of junction A. According to Kirchhoff ’s current law, which states that the total
current into a junction is equal to the total current out of the junction, the current can be stated as Following the current through each of the three branches finds them coming back together at point B. Currents I1, I2, and I3 flows out into junction B, and IT flows out. Kirchhoff ’s current law formula at this junction is the same as at junction
Questions
1. State Kirchhoff’s current law.
2. A total of 3 A flows into a junction of three parallel branches. What is the sum of the three branch currents?
3. If 1 mA and 5 mA of current flow into a junc- tion, what is the amount of current flowing out of the junction?
4. In a parallel circuit with two branches, one branch has 2 mA of current flowing through it. the total current is 5 mA. What is the current through the other branch?
refer to Figure 14-23. What are the values of I2 and I3?