Sundays are ‘little Easters’. They are days of joy. There is no ‘fasting’ or abstinence on Sundays–therefore you should not ‘deprive yourself’ on Sundays of something you like.
Now, if you like studying or reading something, and you want to deprive yourself of it on FRIDAY for your Friday penance, that would be another story! You don’t HAVE to. . .but you COULD!