# Voltage Drop Formula

• Difficulty Level : Medium
• Last Updated : 20 Jan, 2022

Voltage is what makes electric charges move and it is measured in volts (v). So Voltage drop describes how the energy supplied by a voltage source is decreased as electric current runs through electrical circuit parts that do not generate voltage. Because the supply energy is wasted, the voltage drop across conductors, connectors, and internal resistances of the source is undesirable.

In simple words, the voltage drop is the amount of voltage loss that happens through all or part of a circuit because impedance is known as voltage drop.

### Voltage Drop Formula

Voltage drop formula can be shown as,

V = I×Z

Where,

• I = the Current which is measured in Ampere,
• Z = Impedance which is measured in ohms.

Voltage drop is also measured in Volts.

### Sample Problems

Problem 1: A current of 5A is flowing through a closed circuit that has a resistance of 20 Ω. Compute the Voltage Drop across the circuit.

Given: Here, we have

• Current (I) = 5A,
• Impedance (Z) = 20 Ω

Thus according to the Voltage Drop formula,

V = I×Z

Substituting the values of Current (I) and Impedance (Z) in the Voltage drop formula,

V = 5 × 20

V = 100 v

Thus voltage drop is 100v

Problem 2: In a closed circuit, there is a resistor of 50 Ω and a current of 2A. Find the Voltage drop if the current is doubled.

Given: Here, we have

I = 2 A

According to the condition, Current is doubled

• I  = 4 A
• Z = 50 Ω

Thus according to the Voltage drop formula

V = I × Z

V = 4 × 50

V = 200 v

Thus voltage drop is 200v

Problem 3: In a closed circuit, the voltage drop is found to be 100 v and there was a resistance of 20 Ω. Find the current flowing through the circuit at that instance.

Given: Here, we have

• Voltage drop = 100 v
• Z = 20 Ω

Thus rearranging the formula for Voltage drop,

I = V / Z

Substituting the value of Voltage drop and Impedance,

I = 100 v / 20 Ω

I = 5 A

Thus the current flowing from the circuit is 5 Ampere.

Problem 4: In a closed circuit, the voltage drop is found to be 150 v and there was a current of 7 A. Find the Impedance.

Given: Here, we have

• Voltage drop = 150 v
• I = 7 A

Thus rearranging the formula for Voltage drop,

Z = V / I

Substituting the value of Voltage drop and current

Z = 150 / 7

Z = 21.43 Ω

Thus the impudence offered was 21.43 Ω

Problem 5: In a closed circuit with two resistors R1 and R2 in series with values as 15 Ω and 5 Ω respectively and current are 6 A. Find the voltage drop across the circuit.

Given: Here, we have

The total resistance in the circuit is R1 + R2 =  (15 + 5) Ω = 20Ω

• I = 6 A
• Z = 20 Ω

Thus according to the Voltage drop formula,

V = I × Z

V = 6 × 20

V = 120 v

Thus the voltage drop is 120 volts.

Problem 6:  In a closed circuit with two resistors R1 and R2 in series with values as 10 Ω and 2 Ω respectively and Voltage drop of 80 v. Find the current across the circuit.

Given: Here, we have

The total resistance in the circuit is R1 + R2 =  (10 +2) Ω = 12Ω

• V = 80 v
• Z = 12 Ω

Thus rearranging the formula for Voltage drop,

I = V / Z

Substituting the value of Voltage drop and Impedance,

I = 80 / 12

I = 6.67 A

Thus the current flowing from the circuit is 6.6667 Ampere.

Problem 7: In a closed circuit with two resistors R1 and R2 in parallel with values as 8 Ω and 5 Ω respectively and current is 4A. Find the voltage drop across the circuit.

Given: Here we have

The total resistance in the circuit is (1/R1 +1/R2)  = (1/8 + 1/5) Ω = 0.325 Ω

• I  = 4 A
• Z = 0.325 Ω

Thus according to the Voltage drop formula,

V = I × Z

V = 4 × 0.325

V = 1.3 v

Thus the voltage drop is 120 volts.

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