Challenge type: Logic Lights · Difficulty: ★★★★★ Super tricky · Gates: 4
Flip the switches, follow the wires through the gates… will the lamp light up?
In this circuit, switch A is ON, switch B is OFF, switch C is OFF, switch D is ON.
The lamp is wired like this: lamp = (A AND NOT B) OR (C OR D)
How the gates work
- AND is ON only if both of its inputs are ON.
- NOT flips its input: ON becomes OFF, and OFF becomes ON.
- OR is ON if at least one of its inputs is ON.
Work from the switches on the left towards the lamp on the right, one gate at a time.
Need a hint?
Write ON or OFF next to every wire as you go. The wire coming out of each gate depends only on the wires going into it.
For teachers and grown-ups
Skills practised: Boolean logic (AND, OR, NOT), truth values, and step-by-step evaluation.
The big idea: Logic gates make decisions from ON and OFF signals. Millions of them make up every computer chip.
Questions to ask:
- Which switch would you flip to change the lamp?
- When is an AND gate ON? When is an OR gate ON?
- Can you write the circuit as a sentence using and, or and not?
Take it further: Children build truth tables for each gate, then design a circuit for a rule such as 'light the lamp if it is dark AND someone is home'.