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Resistors and Resistance Calculations
Resistors are passive devices used in electronic
circuits to control the flow of current. An ideal resistor has no associated stray capacitance
or inductance, and therefore performs exactly the same in a direct current (DC) circuit
as it does in an alternating current (AC) circuit at any frequency.
| Calculating Resistance from Bulk Resistivity |
As an example of calculating a volume's resistance from its bulk resistivity, consider the drawing to the left. Assume 12 AWG copper wire with a resistivity (from the table) of 1.72x10-6 Ω·cm, a cross-sectional area (A) of 0.03309 cm2, and a length of 1 meter. Per the given formula, its resistance is:
which agrees well with typical specified Ω/km values published by wire manufacturers. Alpha claims 1.59 Ω/1000' or 5.22 Ω/km. |
Equations (formulas) for combining inductors in series and parallel are given below.
| Parallel-Connected Resistors |
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Total resistance of parallel-connected resistors is equal to the reciprocal of the sum of the reciprocals of the individual resistances. Keep units constant. |
| Series-Connected Resistors |
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Total resistance of series-connected resistors is equal to the sum of the individual resistances. Keep units constant. |
| Calculating Resistance from Bulk Resistivity |
|
As an example of calculating a volume's resistance from its bulk resistivity, consider the drawing to the left. Assume 12 AWG copper wire with a resistivity (from the table) of 1.72x10-6 Ω·cm, a cross-sectional area (A) of 0.03309 cm2, and a length of 1 meter. Per the given formula, its resistance is:
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Copyright: 1996 - 2026 |
About RF Cafe RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a lady's voice announced "You've Got Mail" when a new message arrived... |
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