# What are KCL and KVL

## Kirchhoff's laws

The Kirchhoff current and voltage law defined by Gustav Kirchhoff describes the relationship between the values ​​of currents flowing through a connection point and the voltages in a circuit loop in a circuit.

### Kirchhoff's current law (KCL)

This is Kirchhoff's first law.

The sum of all currents entering a circuit junction is 0. The currents entering the junction have a positive sign and the currents leaving the junction have a negative sign: Another way to look at this law is that the sum of the currents entering a transition is equal to the sum of the currents exiting the transition:

#### KCL example

I. 1 and I. 2 enter the intersection

I. 3 leave the intersection

I. 1 = 2A, I. 2 = 3A, I. 3 = -1A, I. 4 =?

Solution:

I. k = I. 1 + I 2 + I 3 + I 4 = 0

I. 4 = -I 1 - I. 2 - I. 3 = -2A - 3A - (-1A) = -4A

There I. 4 is negative, it leaves the intersection.

### Kirchhoff's Voltage Law (KVL)

This is Kirchhoff's second law.

The sum of all voltages or potential differences in a current loop is 0. #### KVL example

V. S. = 12 V, V. R1 = -4 V, V. R2 = -3V

V. R3 =?

Solution:

V. k = V. S. + V. R1 + V. R2 + V. R3 = 0

V. R3 = - V. S. - V. R1 - V. R2 = -12 V. + 4 V. + 3 V. = -5 V.

The voltage sign (+/-) is the direction of the potential difference.