difference between cash & petty cash

Cash means main cash balance of an entity and petty cash means cash given to petty cashier for daily petty expenses like tea, coffee, photostate, etc.

The main cash is maintained in a seperate book called "CASH BOOK", & all the petty expenses incurred by the entity will be maintained in "PETTY CASH BOOK"..

Can anyone pls tell me the limit of petty cash exp per day