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Lesson: Chapter 19 — Current Electricity

19.6. Resistors 5 of 6

Reading a resistor

Four bands, three questions. The order of work is always the same: digits first, then the multiplier, then the tolerance.

Example 1

The problem

Shown below is a fixed resistor obtained from a shop. Its bands are brown, black, red and silver.

  1. Find its resistance value.
  2. What is the tolerance of this resistor?
  3. What is the range of true values this resistor could have?

Figure to be added

Figure for example 1 — a fixed resistor with four bands, the fourth of them silver and set apart from the other three.

Part 1 — the value

Brown = 1, black = 0, red = multiply by 102

value = 10 × 100

= 1000 Ω

Part 2 — the tolerance

The fourth band is silver, so the tolerance = ± 10%

Part 3 — the range

amount the value may vary by = 1000 × 10 ÷ 100 = 100 Ω

range = (1000 − 100) Ω to (1000 + 100) Ω

= 900 Ω to 1100 Ω

Exercise 19.3

The problem

You are supplied with a resistor marked with four colour bands: orange, orange, yellow and gold.

  1. Find the value of the resistor.
  2. What is its tolerance?
  3. Calculate the range of values the resistor may have.

The first two bands are digits, not a number to multiply

Brown and black are 1 and 0, and together they make 10, not 1 × 0. Writing the two digits side by side is the step, and only then does the third band multiply.