Weight. The zinc cents are only 2.5g, and the coppers are 3.11. If you don't have a scale, just take either a pre- or post-'82 cent and balance it with the questioned one. If they balance your questioned coin is the same metal as the known one. If not, the lighter is zinc, the heavier is copper.
I can't help myself, so here is my smart-aleck response: Just drill a hole it it! The copper ones are golden colored inside and the zinc ones are silver colored inside. Sorry about that everyone, but I've been resisting using this answer for quite some time and I just couldn't hold back any longer! P.S. Or you could just weigh them to tell the difference, kinda like Roy said...
Check out this link http://coincollector.org/archives/001915.html I had wondered about 82 pennies too earlier Bruce
I'd always assumed that it was because so few of them speak English fluently enough to pass their entrance exams...or am I missing something? :goofer:
This might be kinda late but... You can also drop them on a hard surface such as a wood table. The copper ones have a full ringing sound, the zinc ones have a dull, fake sound. First try it out with a pre 1982 penny and then a post 1982 penny, I think its very easy to tell the difference.
