Physical coins is one of physical way of storing Bitcoin.There is some company coverting your BTC into physical form.. like Casascius. I'll tell you what I know, So these company they collect Bitcoin. And they make various 1,2,5,10 BTC etc coins as per their wish. What they actually do is, make one unique wallet and in them, transfer particular amount of Bitcoin to that address. After that, they engrave its private key on sticker/hologram/coin and somehow hide it so that whenever, buy has need to transfer them, they remove those sticker/hologram and can send the transaction. Right?
So, I've following questions?
1. Each coin have their own unique address whether it is for 0.001 physical coin or 1000 BTC physical coin?
2. If they only engrave private key in coin then, how do they tell public address to its customer? Do they send letter, certificate or anything like that with Public address?
3. If they're one who knows public address and private address then how can we trust them?
Your understanding is correct. Private keys are hidden some how in coin and public key is very visible.
1. Yes
2. You may get public address on coin visibly, or given you with a accompanying documentation/email or you can go to their web site and get it.
3. You should not trust them.
Regards