Table of Contents
Resistors in Series
When resistors are connected in series, they form a single current path. The same current flows through every resistor, and the total resistance equals the sum of all individual resistances. The supply voltage divides across the resistors proportionally to their resistance values, following Kirchhoff's Voltage Law (KVL).
Series resistor circuits are fundamental building blocks in electronics. They are used in voltage dividers, current limiting, biasing circuits, and signal attenuation networks. Understanding series resistance is essential for designing and analyzing virtually every electronic circuit.
Series Resistance Formulas
Voltage Divider Effect
| Resistor | Resistance | Voltage Drop (12V supply) | % of Total |
|---|---|---|---|
| R1 | 100 Ω | 1.85 V | 15.4% |
| R2 | 220 Ω | 4.06 V | 33.8% |
| R3 | 330 Ω | 6.09 V | 50.8% |
| Total | 650 Ω | 12.00 V | 100% |
Power Dissipation
- Total power: P = V × I = I² × Rtotal = V² / Rtotal
- Power per resistor: Pn = I² × Rn
- The largest resistor dissipates the most power in a series circuit.
- Always check that each resistor's power rating exceeds its actual dissipation with a safety margin.
Frequently Asked Questions
What happens if one resistor in series fails open?
If any resistor in a series circuit fails as an open circuit, the entire circuit is broken and no current flows. This is because there is only one current path. This is a key disadvantage of series circuits compared to parallel circuits, where other paths remain functional.
How does current behave in a series circuit?
Current is the same at every point in a series circuit. Whether you measure before R1, between R1 and R2, or after the last resistor, the current is identical. Only the voltage changes from point to point as it drops across each resistor.
Can I use series resistors as a voltage divider?
Yes, two or more series resistors form a voltage divider. The voltage at any node between resistors is proportional to the resistance below that node divided by the total resistance, multiplied by the supply voltage. However, voltage dividers are affected by load current, so they work best with high-impedance loads.