# Is it possible to explain a transistor (or vacuum tube or relay) using a marble-based switch for students?

In Japan I saw a simulation of internet based communication in the The National Museum of Emerging Science and Innovation (Miraikan). It attempted to replicate ascii characters moving along a 8 part wire using combinations of marbles rolling along.

I've just finished reading Charles Petzold's book, Code: The Hidden Language of Computer Hardware and Software. In it Charles explains building relays into gates, gates into logic components, and logic components into computing machines.

I wondered if a mechanism existed that simulated a switch using marbles.

My question is: Is it possible to explain a transistor (or vacuum tube or relay) using a marble-based switch for students?

• Definitely related. I love Mammoths. Jan 3, 2017 at 10:13
• It could be done like this. Jan 3, 2017 at 10:29
• Yes, it can be done but be careful not to push the analogy too far. Marbles don't behave like electrons Jan 3, 2017 at 10:43

I'd be thinking of something like this:

The top hopper contains blue marbles (so you can see where things come from). A spring loaded flap prevents anything falling.

Drop a red marble into 'base' tube ( = small base current) - it opens the flap momentarily, marbles drop from the 'collector' hopper and the red ('base' marble) and blue ('collector') marbles accumulate in "emitter' container below.

Flap then closes due to spring action (that's the tricky mechanical part).

The gain of the 'transistor' is then determined by how many blue marbles fell for a single red marble. Analogy gain = collector current/base current.

We also can see Kirchoff's current law in action -

the number of 'emitter' marbles = number of collector marbles + the base marble

or the analogy emitter current = base current + collector current

Hope this gives you some ideas.

• Nice idea - but it cannot work. One red marble will not have enough power (mass, force) for opening the window for so many blue marbles (mass and weight much larger). I hope that you will understand what I mean (sorry for my bad english). Please note, that even this simple example again shows that the BJT is NOT a current-controlled device. It is the VOLTAGE VBE that controls IE resp. IC.
– LvW
Jan 3, 2017 at 12:13