Electronic components – tolerance band for a carbon resistor A carbon resistor has the colour bands green–blue–yellow (value bands shown, but no separate tolerance band). What is the tolerance of this resistor?

Introduction:
Resistor colour coding conveys both nominal resistance and tolerance. When a dedicated tolerance band (usually gold, silver, or none) is absent, the default tolerance must be inferred. This question checks recognition of the standard E-series coding convention for carbon resistors.

Given Data / Assumptions:

• Three visible bands: green, blue, yellow (digits and multiplier).
• No fourth band (tolerance) explicitly present.
• Standard 4-band code conventions apply; if the tolerance band is missing, default tolerance is used.

Concept / Approach:

In the 4-band scheme: Band 1 = first digit, Band 2 = second digit, Band 3 = multiplier, Band 4 = tolerance. If the tolerance band is missing (i.e., only the first three bands are given), the resistor is taken to have the default tolerance of ± 20% for carbon composition/carbon film types, as per conventional coding used widely in legacy components and many educational contexts.

Step-by-Step Solution:

Verification / Alternative check:

By contrast, a gold band indicates ± 5%, silver indicates ± 10%. Their absence defaults to ± 20%, confirming the choice.

Why Other Options Are Wrong:

± 5% and ± 10% require gold or silver bands; ± 30% is nonstandard in the typical modern code; ± 1% would require brown tolerance band in a 5-band or special series resistor.

Common Pitfalls:

Reading the third value band as tolerance; assuming every resistor must show a tolerance band explicitly.

Final Answer:

± 20%