Mirror Maze Puzzles

Bounce the beam and predict the exit

A laser enters from the left edge of the grid. The grid contains mirrors set at 45 degrees, each drawn as a / or a \\, and every one turns the beam through a right angle. Follow the bounces and work out which edge cell it leaves from.

You need a pencil to check the answer, not to find it. Holding the bounces in your head instead of drawing them is what makes a small grid harder than it looks.

Reading a mirror

Two mirrors, four incoming directions, eight outcomes. That is the whole rule set, and it is small enough to be learned in a minute and easy enough to get wrong at speed.

A beam travelling east that meets a / turns north. The same beam meeting a \\ turns south. Going west, the two swap. It is worth having a class work out all eight cases on the board before the first sheet, because a solver who is reconstructing the rule at every mirror will lose track by the fourth bounce.

The decoys are the difficulty

Roughly half as many decoy mirrors as the grid is wide are scattered around, placed so that they do not touch the true beam path.

They do nothing at all, and that is exactly why they work. A mirror sitting one row above the beam pulls the eye, and once it is included the beam sets off on a different route that also reaches an edge and also looks correct. A wrong answer here is as convincing as a right one, which is unusual in a puzzle and is the whole reason to work slowly.

Size

Six, eight, ten or twelve cells square. Eight is the default.

Six is a couple of bounces and suits a first attempt. Twelve gives a long path with plenty of decoys and is a genuine adult puzzle — the beam can cross its own earlier route, which is where most errors happen, because the eye picks up the wrong line at the crossing.

The solution page

Turn it on and the beam's path is drawn in, bounce by bounce. It is worth having when you are teaching the rule, since the useful conversation is not "you were wrong" but "which mirror did you take that you should not have".

What it is actually practising

Reflection and angle, obviously, and it makes a decent hook for the physics of it. But the transferable part is holding a state in your head while applying a rule repeatedly — position and direction, updated eight or twenty times, with no notes.

Every layout is generated with a real beam path already traced, so the puzzle always has an answer. Print at 100% on A4 or US Letter.