Resistor colour code – compute value with tolerance A carbon resistor shows the bands red–red–black–silver. Determine its resistance value (with tolerance).

Introduction:
Four-band resistor codes use two significant digits, a multiplier, and a tolerance band. Correctly reading the colours prevents order-of-magnitude mistakes in circuit assembly and troubleshooting.

Given Data / Assumptions:

• Bands: 1st = red, 2nd = red, 3rd (multiplier) = black, 4th (tolerance) = silver.
• Standard 4-band colour code chart.
• Ohmic value sought in Ω with tolerance.

Concept / Approach:

Digits: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. Multiplier: black = 10^0 = 1. Tolerance: silver = ± 10%. Thus the first two bands form the number 22, multiplied by 1, and tolerance from silver is ± 10%.

Step-by-Step Solution:

Verification / Alternative check:

If the multiplier were brown, value would be 220 Ω; if gold were the tolerance band, it would be ± 5%. The provided colours uniquely determine 22 ± 10% Ω.

Why Other Options Are Wrong:

2200 Ω and 22000 Ω require brown or red multipliers; ± 5% needs gold; 2.2 kΩ would need red–red–red–silver or equivalent.

Common Pitfalls:

Reading the bands from the wrong end; confusing black multiplier (×1) with digit 0 in the first position (first band is never black).

Final Answer:

22 ± 10% Ω