apps free but card is charged i have saved one card details with my app id as it does not allow u to browse the itune store without that . 

Now i try downloaidng few free apps for ipad . After sometime i recivied notifcation from my bank that a purchase has been made on my card for the same FREE app . 

Why if a app is free , am i charged for the same ?
or if it is not free , why does it say free on the itune store . 
Not a very good itune store experience :(
These free apps that you downloaded, did you run the app and buy something within the app? 

Nowadays, apps can sell you certain features (like more functionality or tokens in case of games). These purchases are called In-App Purchases (IAP) and they are charged towards your card. 

If you downloaded apps or games that have In App Purchases and you want to make sure that you don't make these purchases by mistake (kids make this mistake many times), then go to you iPhone's Settings --> General --> Restrictions --> Enable Restrictions and then under Allowed Content, turn off In-App Purchases. This will stop anyone from spending money.

If, however, you are being charged for the app itself, you should contact Apple support and they will look into the matter and explain what is happening, maybe even give you a refund.