Find Voltage Across Each Resistor Calculator

Enter the total voltage and the resistance values for up to three resistors in series to find the voltage drop across each one.

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Summary of resistance, voltage drop, and voltage percentage for each resistor.

Component	Resistance (Ohms)	Voltage Drop (Volts)	Percentage of Total Voltage
Resistor 1 (R1)	100	1.52	12.66%
Resistor 2 (R2)	220	3.34	27.85%
Resistor 3 (R3)	470	7.14	59.49%
Total	790	12.00	100%

What is a Voltage Across Each Resistor Calculator?

A Voltage Across Each Resistor Calculator is a tool designed to determine the voltage drop across individual resistors connected in an electrical circuit, particularly a series circuit. When resistors are connected in series, the total voltage supplied by the source is divided among them, and the voltage drop across each resistor is proportional to its resistance. This calculator helps students, hobbyists, and engineers quickly find these voltage values without manual calculations, especially when using Ohm's Law and the principles of series circuits.

This specific Voltage Across Each Resistor Calculator focuses on series circuits because, in a parallel circuit, the voltage across each resistor is simply equal to the source voltage. For series circuits, the current is the same through all resistors, but the voltage divides. The calculator takes the total voltage and the individual resistance values as inputs to compute the total current and then the voltage across each resistor.

Anyone working with electronic circuits, from students learning basic electronics to technicians troubleshooting circuits or engineers designing them, can benefit from using a Voltage Across Each Resistor Calculator. Common misconceptions include thinking the voltage is the same across all resistors in series (it's not, unless all resistances are equal) or that the calculator applies to any circuit configuration (this one is for series circuits).

Voltage Across Each Resistor Calculator Formula and Mathematical Explanation

To find the voltage across each resistor in a series circuit, we use Ohm's Law and the properties of series circuits:

1. Calculate Total Resistance (R_T): In a series circuit, the total resistance is the sum of individual resistances:
   R_T = R₁ + R₂ + R₃ + … + R_n
2. Calculate Total Current (I_T): According to Ohm's Law (V = IR), the total current flowing through the series circuit is the total voltage (V_T) divided by the total resistance (R_T):
   I_T = V_T / R_T
   In a series circuit, the current (I_T) is the same through every resistor.
3. Calculate Voltage Across Each Resistor (V_n): Using Ohm's Law again for each individual resistor, the voltage drop across resistor R_n (V_n) is the total current (I_T) multiplied by the resistance of that resistor (R_n):
   V₁ = I_T * R₁
   V₂ = I_T * R₂
   V₃ = I_T * R₃
   …
   V_n = I_T * R_n

The sum of the individual voltage drops across all resistors in a series circuit will equal the total source voltage (Kirchhoff's Voltage Law): V_T = V₁ + V₂ + V₃ + … + V_n.

Variables Used in the Voltage Across Each Resistor Calculator

Variable	Meaning	Unit	Typical Range
VT	Total Voltage/Source Voltage	Volts (V)	0.1 V – 1000s V
R1, R2, R3…	Resistance of individual resistors	Ohms (Ω)	1 Ω – 10 MΩ
RT	Total Resistance	Ohms (Ω)	Calculated
IT	Total Current (same through each resistor)	Amperes (A) or milliamperes (mA)	Calculated
V1, V2, V3…	Voltage drop across individual resistors	Volts (V)	Calculated

Practical Examples (Real-World Use Cases)

Let's see how the Voltage Across Each Resistor Calculator works with practical examples.

Example 1: LED Circuit with Current Limiting Resistors

Suppose you have a 9V battery and you want to connect three LEDs, but each needs a different current limiting resistor in series with it, and those three branches are then part of a larger series circuit (for simplicity, let's assume the resistors are just in series with each other and the source for this example, though typically they are with LEDs). Imagine three resistors R1=100Ω, R2=150Ω, and R3=220Ω in series with a 9V source.

• V_T = 9V
• R₁ = 100Ω
• R₂ = 150Ω
• R₃ = 220Ω

Using the Voltage Across Each Resistor Calculator:

1. R_T = 100 + 150 + 220 = 470Ω
2. I_T = 9V / 470Ω ≈ 0.01915A (19.15mA)
3. V₁ = 0.01915A * 100Ω ≈ 1.915V
4. V₂ = 0.01915A * 150Ω ≈ 2.872V
5. V₃ = 0.01915A * 220Ω ≈ 4.213V

The voltages across the resistors are approximately 1.92V, 2.87V, and 4.21V, summing up to 9V.

Example 2: Voltage Divider Network

A voltage divider uses series resistors to produce a lower voltage from a higher voltage source. Suppose you have a 12V supply and need about 4V. You might use two resistors, R1=2kΩ (2000Ω) and R2=1kΩ (1000Ω) in series. We want the voltage across R2.

• V_T = 12V
• R₁ = 2000Ω
• R₂ = 1000Ω
• R₃ = 0Ω (as we only have two)

Using the Voltage Across Each Resistor Calculator:

1. R_T = 2000 + 1000 = 3000Ω
2. I_T = 12V / 3000Ω = 0.004A (4mA)
3. V₁ = 0.004A * 2000Ω = 8V
4. V₂ = 0.004A * 1000Ω = 4V
5. V₃ = 0V (as R3=0)

The voltage across R2 is 4V, as desired for the voltage divider output.

How to Use This Voltage Across Each Resistor Calculator

1. Enter Total Voltage (V_T): Input the voltage supplied by the source to the series circuit in the "Total Voltage" field.
2. Enter Resistance Values (R₁, R₂, R₃): Input the resistance values for each resistor in the series circuit in the respective fields. If you have fewer than three resistors, enter 0 for the unused ones.
3. Calculate: Click the "Calculate Voltages" button or simply change input values; the results will update automatically if you use the `oninput` event.
4. View Results:
   • The "Primary Result" section will highlight the voltage drops across each resistor (V₁, V₂, V₃).
   • "Intermediate Values" will show the Total Resistance (R_T), Total Current (I_T), and individual voltage drops again.
   • The table summarizes the resistances, voltage drops, and percentage of total voltage for each resistor.
   • The chart visually represents the voltage drops across the resistors.
5. Reset: Click "Reset" to return to the default values.
6. Copy Results: Click "Copy Results" to copy the main findings to your clipboard.

Use the results to understand how voltage is distributed in your series circuit or to design voltage dividers.

Key Factors That Affect Voltage Across Each Resistor

1. Total Voltage (V_T): A higher total voltage, with the same resistances, will result in proportionally higher voltage drops across each resistor because the total current increases.
2. Individual Resistance Values (R_n): The voltage drop across a resistor is directly proportional to its resistance (V=IR). A larger resistance will have a larger voltage drop compared to a smaller resistance in the same series circuit.
3. Ratio of Resistances: The voltage divides among the series resistors based on the ratio of their resistances to the total resistance. A resistor that is half the total resistance will drop half the total voltage.
4. Total Resistance (R_T): The total resistance influences the total current. If total resistance increases (e.g., adding more resistors or using higher values), the total current decreases, affecting all individual voltage drops.
5. Number of Resistors: While not a direct factor in the formula for a specific resistor's voltage drop (given I_T), adding more resistors increases R_T, reduces I_T, and redistributes the voltage.
6. Circuit Configuration: This Voltage Across Each Resistor Calculator assumes a simple series circuit. If resistors are in parallel or in a series-parallel combination, the calculation method changes significantly. In parallel, voltage is the same; in series-parallel, equivalent resistances must be found first. Our Series Circuit Calculator and Parallel Circuit Calculator can help with those.

Frequently Asked Questions (FAQ)

What happens if I enter 0 for all resistances?

The total resistance will be 0, leading to a division by zero when calculating current. The calculator will handle this and show an error or very high current, which in reality would be a short circuit.

Does this calculator work for AC circuits?

This calculator is primarily for DC circuits or AC circuits with purely resistive loads where phase shifts are not considered. For AC with capacitors or inductors, impedance would be used instead of resistance. Our Ohm's Law Calculator might be useful too.

What if I have more than three resistors?

This specific calculator is set up for up to three. For more, you would sum all resistances to get R_T, find I_T, and then V_n = I_T * R_n for each.

Why is the current the same through all resistors in series?

In a series circuit, there's only one path for the current to flow. Like water in a single pipe, the flow rate (current) must be the same at all points.

What is Kirchhoff's Voltage Law (KVL)?

KVL states that the sum of all voltage drops around any closed loop in a circuit must equal the sum of the voltage sources in that loop. In a simple series circuit, it means V_T = V₁ + V₂ + V₃ + …

How does a voltage divider work?

A voltage divider uses two or more resistors in series to tap off a fraction of the total voltage across one of the resistors. The voltage across a resistor R₂ in series with R₁ is V₂ = V_T * (R₂ / (R₁ + R₂)).

Can I use this for resistors in parallel?

No. In a parallel circuit, the voltage across each resistor is the same and equal to the source voltage. You would use a Parallel Circuit Calculator to find individual currents and total resistance.

What if one of my resistors is very large compared to others?

The resistor with the largest resistance will have the largest voltage drop across it in a series circuit.

Related Tools and Internal Resources

• Ohm's Law Calculator: Calculate voltage, current, resistance, or power using Ohm's Law (V=IR, P=VI).
• Series Circuit Calculator: Analyze circuits with components connected in series, finding total resistance, current, and voltage drops.
• Parallel Circuit Calculator: Analyze circuits with components in parallel, finding equivalent resistance and branch currents.
• Resistor Color Code Calculator: Determine the resistance value and tolerance based on the colored bands on a resistor.
• Power Calculator: Calculate electrical power given voltage, current, or resistance.
• Current Calculator: Calculate current flow based on voltage and resistance or power.