Apprentice path · Stage 6: The quantities behind every calculation · Lesson 20

Voltage, current, resistance

Voltage is the push, current is the flow, and resistance is what fights the flow.

Why this matters on the job

Every calculation you will ever do rests on these three. Getting the words straight first is what stops the formulas from feeling like memorised noise.

How to think about it

  1. Voltage is electrical potential difference -- a difference between two points, never a property of one point.
  2. Current is the rate of charge flow.
  3. Resistance opposes current.

Worked through

Hold the resistance still and raise the DC voltage: the current goes up. That is the whole relationship in one sentence, and it is why a battery, a conductor and a resistor are enough to demonstrate all three at once -- the battery supplies the push, the conductor carries the flow, the resistor opposes it.

Check yourself: You double the DC voltage across a fixed resistance. What happens to the current?

Answer: It doubles.

With resistance unchanged, current follows voltage directly -- more push through the same opposition gives proportionally more flow.

Watch out for: Saying a point "has voltage". Voltage is always between two points. If someone tells you a conductor is at 120 volts, the question you have not asked yet is: relative to what?
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Written from the owner's poster for this lesson. Nothing added beyond what the poster states.

Written for Texas apprentices as free study material. The Texas apprentice licence is an application, not an exam (Occupations Code 1305.161), and nothing here counts as apprenticeship hours or continuing-education credit. VoltMark is not affiliated with, endorsed by, or sponsored by NFPA, PSI, TDLR, or any state or local licensing authority. Always follow your employer's safety programme and your supervising electrician.