Voltage, current & resistance
Voltage is electrical pressure. More precisely, it’s the difference in electrical potential between two points, measured in volts (V). The “between two points” part matters. A voltage never exists at a single point, the same way water pressure only means something as a difference between two tanks. A 9 V battery holds its + terminal nine volts above its − terminal, and if you connect a path between them, that pressure pushes charge around it.
Current is the flow itself: the amount of charge passing a point each second, measured in amperes (A). Resistance, in ohms (Ω), is how hard a material fights that flow. Copper wire has almost none. A resistor adds a deliberate, known amount. Push the same voltage through more resistance and less current flows, which is the relationship the next lesson pins down.
This shapes how you use a multimeter on a real board. You read voltage across a component, with a probe on each side while the circuit runs, but you read current through it, with the meter inserted into the path. Probing “the voltage at a point” only works because the black probe supplies the second point, usually ground.
Key points
- Voltage (V) is a difference in potential between two points, never a property of one point alone.
- Current (A) is the rate charge flows past a point, and it’s the same everywhere along one unbroken path.
- Resistance (Ω) opposes current. Wires have almost none; resistors add a controlled amount.
- Measure voltage across a part and current through it. Wiring an ammeter in parallel is the classic way to blow its fuse.
Practice
0 of 3 answered · Not startedWrong answers just let you try again, and hints are there if you want them. Answering every question first time, without hints, is what earns mastery.
- 1
You want to measure the current through an LED. How does the meter go into the circuit?
- 2
Why is it meaningless to say "the voltage at pin 3 is 3.3 V" without any other context?
- 3
Which of these are measured across a component rather than through it?
Select every answer that applies.
