I propose a Fermi Problem.

*Over the lifetime of an average light bulb, what is the total mass of all the electrons that have flowed through?*

Work on that if you have an idea how to proceed, or just take your best plausible guess. Remember it’s a Fermi problem, so we’re looking for estimates rather than detailed calculations. My suggested solution method under the link.

Ok, here’s my rough shot. Each electron will transfer energy to the bulb roughly equal to the energy associated with the potential of the electric field produced by the voltage at the plug. For wall current, that’s about 120 volts. That times the electron charge gives you, oh, about 2e-17 joules per electron. A good old-fashioned energy-eating incandescent might burn 75 watts, where a watt is of course one joule per second.

Divide the energy per time divided by energy per electron gives time per electron. Doing the division, I get about 4e18 electrons per second. Electrons are very, very light. They have a mass of around 9e-31 kilograms, which multiplied by our electron flow rate gives 3.5e-12 kilograms per second. That’s trillionths of a kilogram, so not a whole lot.

But bulbs last a while. Maybe 1000 hours? Multiply that by the mass rate (remembering the unit conversions), and I get about 13ish milligrams. Not big, but still macroscopic. It’s about the mass of a very tiny pebble.

To be honest this was a little surprising to me. I’s have guessed it would be smaller. But having the numbers tell you something unexpected is sometimes even more interesting,