Resistance and Ohm’s Law
Lesson 2 of 12 — Electronics Fundamentals. In Lesson 1 you met voltage (the electrical “push”) and current (the flow of electric charge). This lesson adds the third member of the family — resistance — and then ties all three together with the single most important formula in all of electronics: Ohm’s Law.
The big idea
Electricity is not magic. In a simple circuit, three quantities dance together in a completely predictable way:
- Voltage (V), measured in volts — how hard the battery pushes the charge.
- Current (I), measured in amperes (amps, A) — how much charge actually flows per second.
- Resistance (R), measured in ohms (symbol $\Omega$, the Greek letter omega) — how much the material fights the flow.
Ohm’s Law says these three are locked together by $V = I \times R$. If you know any two, you can always calculate the third. That is why this one equation shows up on almost every page of the rest of the course.
What you will be able to do after this lesson
- Explain what resistance is and why every real material has some.
- Name the four things that change a wire’s resistance.
- Use Ohm’s Law in all three forms — $V=IR$, $I=V/R$, $R=V/I$ — with the triangle memory trick.
- Predict how current changes when you change voltage or resistance (proportional thinking).
- Calculate electrical power in watts with $P = V \times I$ and $P = I^2 R$.
- Work out the correct protective resistor for an LED — the classic first electronics calculation.
- Understand why wet skin and electricity are a dangerous combination.