Human battery exhibit

The exhibit you describe has four large metal plates, one each copper and aluminum on each side of a meter. The copper plate on the left is connected through the meter to the aluminum plate on the right and the other two plates are connected in the reverse direction. The meter measures micro amperes, or millionths of an amp of current, so it is very sensitive.

Placing one's hands on plates connected across the meter causes the needle to deflect. This is because we, the human, are acting as the electrolyte in a battery. The two metals have different affections for their electrons, and the one that is greedier steals electrons from the one more generous through our bodies. This causes an imbalance between the two plates which is corrected by the current through the meter.

A typical visitor gets a modest reading on the meter. Sometimes a person is able to easily pin the meter at one end of its range. There might be a number of reasons for this. Larger hands and greater pressure produce more current. Moister hands work better than dry hands. I don't know if this is a real affect, but I have an impression that it is common for women to get higher readings than men. I can't imagine an explanation for this, and I am pretty good at making stuff up. I doubt it is because the average man has a greater wingspan than the average woman, but I really don't know. There is also probably a day-to-day variation with an individual depending on personal chemistry, hydration, sweaty palms, etc. I have never studied that, either.

Some of my favorite questions are those I can answer, "I don't know."

Human Battery Question

You ask if there would be an electrical current if one of the plates were made of rock.

The short answer is no. Unless the rock is a very rich metal ore, rock will not conduct electricity well enough to allow a current.

When we put our hands on the metal plates, we complete a circuit, electricity flows from one plate to the other through our arms and body, and then back to the original plate through the micro-ammeter via wires. The current, which is very small, is caused by the different way the metal plates react to the moisture in our skin; one collects electrons and the other gives them up. Any two different conductors will serve the purpose. Ours are copper and aluminum; but they need to be conductors in order to complete the electrical circuit. The human body is a pretty good conductor.

Most rocks are insulators and can't complete the circuit.