The AND Gate: Two Switches and a Lamp
Before level 3 the game offers a short interactive intro: you flip switches and formulate the AND rule yourself. This page tells the same story in text.
Experiment: two switches and a lamp
The circuit has two switches, A and B, and a lamp Q. Toggle them and watch when exactly Q lights up. Going through all four combinations gives the answer: the lamp is on only when A=1 and B=1; in the other three cases it stays dark.
That is the AND rule: the output is 1 only when every input is 1.
The AND rule as a table
What you checked by clicking is written as rows. Columns A and B are the inputs, Q is the output:
| A | B | Q |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Transfer: a chain of two ANDs
Then the intro complicates the circuit: two AND gates are chained, and there are three inputs. Before clicking, guess when Q will light up. The answer: only when all three are on. The first AND demands A and B, the second adds C on top of their one.
Where it is used
An AND gate is about simultaneous conditions. A washing machine heats water only when the door is closed AND the start button is pressed. In a processor, this is how "if both conditions hold" checks work. AND is also access control: a system fires only when both keys are turned.