Cash deposit above 2.5 lacs

If we do a cash deposit of total 17 lacs split as 8 lacs between my mother and me within the 50 day period i.e.from 10th nov-30th dec. What are the tax implications considering the fact that we both file returns and come under 10% tax bracket. Also what would be the amount of tax and penalty to be paid on these cash deposits as this was undisclosed income over a number of years.