Reading the bands in order
Color bands exist because tiny resistors don't have room to print numbers on them. Each color stands for a digit, and the bands are read left to right, starting from the end furthest from the tolerance band — the tolerance band (commonly gold or silver, sitting a little apart from the rest) marks which end is last.
| Color | Digit | Множител |
|---|---|---|
| черен | 0 | ×1 |
| Brown | 1 | ×10 |
| Red | 2 | ×100 |
| Orange | 3 | ×1,000 |
| Yellow | 4 | ×10,000 |
| Green | 5 | ×100,000 |
| Blue | 6 | ×1,000,000 |
| Violet | 7 | ×10,000,000 |
| Сив | 8 | ×100,000,000 |
| Бяло | 9 | ×1,000,000,000 |
On a 4-band resistor, the first two bands are significant digits, the third is the multiplier, and the fourth is tolerance. A brown-black-red-gold resistor reads: 1, 0, ×100, so 10 × 100 = 1,000 Ω (1 kΩ), ±5%.
Brown-Black-Red-Gold = 1, 0, ×100, ±5%
= 10 × 100 = 1,000 Ω ± 5% (950–1,050 Ω)
5-band resistors use three significant digits before the multiplier, giving finer precision — useful for tighter-tolerance parts. 6-band resistors add a final temperature coefficient band, which tells you how many parts per million the resistance shifts for every degree Celsius of temperature change.
Combining resistors: series vs. parallel
Resistors in series share the same current path one after another, so their resistances simply add. Resistors in parallel share the same two connection points, giving current multiple paths to flow through, which is why the combined resistance is always lower than any single resistor in the group.
Series: R_total = R1 + R2 + R3 + …
Parallel: 1/R_total = 1/R1 + 1/R2 + 1/R3 + …
Two 100 Ω resistors in series total 200 Ω. The same two resistors in parallel work out very differently:
1/R_total = 1/100 + 1/100 = 2/100
R_total = 100/2 = 50 Ω
Като пряк път, два равни резистора в паралел винаги се комбинират до точно половината от стойността на един от тях - полезно за бърза проверка на разума, преди да се доверите на по-сложно изчисление с несъответстващи стойности.
Checking power dissipation against a resistor's rating
Every resistor has a maximum power rating — commonly 1/4 watt for small through-hole parts in low-voltage electronics, higher for parts built to handle more heat. Before wiring one into a circuit, it's worth checking that the power it will actually dissipate stays comfortably under that rating.
P = V² ÷ R
12V across a 100 Ω resistor: P = 144 ÷ 100 = 1.44 W
Този пример би изгорил типичен 1/4-ватов резистор почти незабавно - той се нуждае от част, оценена за поне 2 вата, с оставащо пространство като запас на безопасност. Пускането на резистор близо до неговата номинална граница съкращава живота му и може да измести действителната му стойност на съпротивление от отпечатаната, докато се нагрява.
Why resistor values look so specific
Resistors aren't manufactured in every possible value — they follow preferred-number series (E-series) spaced so that, combined with a given tolerance, every practical resistance is covered without huge gaps or wasteful overlap. E12 (12 steps per decade) suits ±10% parts, E24 suits ±5%, and E96 packs in enough steps for ±1% precision resistors. That's why you'll see resistors labeled 4.7 kΩ or 220 Ω rather than a round 5,000 or 200 — those odd-looking numbers are the E-series values.
Свързани електрически изчисления
След като знаете стойността на резистора,Калкулатор по закона на Ом solves for voltage, current, or power in the circuit it's part of, and the electricity calculator covers the broader set of power and cost formulas for a full circuit or appliance.