Kirchhoff's Voltage Law

Statement: The sum of voltage rise in any electrical circuit is equal to the sum of voltage drops in that circuit.

Consider an electrical source with a voltage source which connects with three resistors. R1, R2 and R3. The sum of voltage drops across these resistors is equal to the sum of the input voltage(voltage rise).

Here are a few examples of KVL which help you to learn it in a better way:

Example 1: A 15 V input source powers three resistors, having a series current of 2 mA flowing through them. Find the voltage across R3.

Step 1: Using Ohm's law find the voltage drop across the first resistor.
V = IR = 2 mA* 2 kohm = 4 V

Step 2: Applying KVL:
V_rise = V_drop
15 V = 4 V + 5 V + V_R_3
V_R_3 = 15 V - 5 V - 4 V = 6 V

Example 2: A 20 V source powers three series resistors. The wattage rating of the first one being 30 watts having a current of 3 A flowing through it. The second resistance has all parameters unknown. Whereas, the third one has a voltage drop of 5 V across it. Find all unknown voltages in the circuit.

Step 1: Using formulas P = VI, or V = P/I = 30 watt/3 A = 10 V

Step 2: Using KVL;
V_rise = V_drop;
20 V = 10 V + V_R_2 + 5 V
or V_R_2 = 15 V

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