Sound enters your ear as waves. If you hear a high-pitched sound, short waves arrive in your ear. If you hear a low-pitched sound, these are long waves.
Usually, you can’t see these waves. But here you can! You can see the water splashing when some of the pitches are used. That’s because the waves are exactly long enough! The sound waves reach the end of the tube and rebound at the perfect moment. These reflected waves will strengthen or weaken the other waves in certain places. That’s how you get a standing wave.
You can recognise them by the typical nodes (points that stand still) and antinodes (points that move up and down the most). In this Kundt’s tube, you can see the antinodes as splashing water.
Standing wave in a skipping rope
If two people each take one end of a skipping rope, they can also make standing waves. One person stands still, the other swings up and down. Where the rope hardly moves, there is a node. Where the curve in the rope is the biggest, you’ll see an antinode.
Can you make three antinodes like that?
Standing waves in a microwave oven
Why does your food rotate in a microwave oven?
You heat your food with microwaves. These waves also collide with the walls and bounce back, which results in standing waves. This means you will find nodes and antinodes in fixed places. Where there are antinodes, it gets hot. At the nodes, it stays cold. A pancake of which a part is still cold… not very tasty. That’s why the plate rotates and everything gets heated equally.
