The three numbers that describe every circuit
Before we can talk about transistors as electrical devices, we need three vocabulary words: voltage, current, and resistance. Together they describe everything happening in any circuit, from a flashlight to a 100-billion-transistor processor.
Key Concept
Voltage (V)
Electrical pressure — the force that pushes electrons through a wire. Measured in volts (V). A modern chip runs on roughly 0.7 – 1.2 V; a wall outlet is 120 V; a lightning bolt is millions of volts.
Key Concept
Current (I)
The actual flow of electrons past a point per second. Measured in amperes (A). One amp ≈ 6.24 × 10¹⁸ electrons per second. Inside a chip we usually deal with milliamps (mA, 0.001 A) per circuit and microamps (µA) per transistor.
Key Concept
Resistance (R)
How strongly a material opposes current flow. Measured in ohms (Ω). Copper wire ≈ 0.01 Ω; a chip resistor ≈ 100 – 100 000 Ω; an insulator ≈ trillions of Ω.
The water-pipe analogy
Imagine a water tower feeding a hose. **Voltage** is the water pressure from the tower — push. **Current** is how many liters per second actually flow out the end. **Resistance** is how narrow the hose is — a wider hose lets more water through at the same pressure, a kink chokes it down. Raise the tower (more voltage) or widen the hose (less resistance), and you get more flow (current).
Key Concept
Ohm's Law (V = I × R)
The fundamental rule of every circuit: voltage equals current times resistance. Know any two, and the third is fixed. Engineers rearrange this constantly: I = V/R (find the current through a resistor) and R = V/I (find the resistance from a measurement).
Interactive · Ohm's Law live calculator
Lock:Locked value stays fixed; the other two satisfy V = I × R
5.00 V
50 mA
locked
100 Ω
Ohm's Law: V = I × R → 5.00 V = 0.050 A × 100 Ω
Checkpoint · +5 XP
If V = 5 V and R = 1000 Ω, what is the current?
Why mA and nm matter for chip design. A single transistor handles microamps of current and switches across nanometers of channel. The full chip pulls tens of amps because billions of those tiny transistors switch at the same time. The art of chip design is keeping each transistor low-current while making the system as a whole massively parallel.
Lesson Summary
- Voltage = electrical pressure (volts, V).
- Current = how many electrons flow per second (amps, A; in chips, milliamps mA).
- Resistance = how much the path opposes that flow (ohms, Ω).
- Ohm's Law ties them together: V = I × R. Change two — the third follows.
Test Your Knowledge · +50 XP
1
Voltage is best described as:
2
Current is measured in:
3
Ohm's Law states:
4
Which best matches the water-pipe analogy?
5
A 1.0 V supply pushes 100 mA through a load. The resistance is: