N2CUASPARKA Lab

T5D · Ohm’s Law and circuits

Ohm's Law, Series & Parallel

The formulas and circuit relationships that turn electrical quantities into useful numbers.

Practical takeaway

Ohm's Law tells you how voltage, current and resistance interact. Series circuits have one current path; parallel branches share the same two connection points.

Technician exam focus

Be able to choose and use E = I × R, I = E ÷ R and R = E ÷ I, then remember: same current in series, same voltage in parallel.

1. Ohm's Law

E = I × RVoltage = current × resistance
E = I × RFind voltage: multiply.
I = E ÷ RFind current: E is on top.
R = E ÷ IFind resistance: E is on top.

The triangle can be a memory aid if you like it, but you do not need it. The clean pattern is: when Ohm's Law uses division, E is the numerator.

2. Worked Technician examples

90 V ÷ 3 A= 30 Ω
12 V ÷ 1.5 A= 8 Ω
12 V ÷ 4 A= 3 Ω
120 V ÷ 80 Ω= 1.5 A
200 V ÷ 100 Ω= 2 A
240 V ÷ 24 Ω= 10 A
0.5 A × 2 Ω= 1 V
2 A × 10 Ω= 20 V

3. Series and parallel

SeriesOne path through every componentSame current
ParallelBranches connect across the same two pointsSame voltage

Fast check: Series → same current. Parallel → same voltage.

T5D checklist

  • E = I × R.
  • I = E ÷ R.
  • R = E ÷ I.
  • Series circuit → current is the same through all components.
  • Parallel circuit → voltage is the same across all components.
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