python "in" function works differently for lists and numpy arrays

If I have a list of tuples, the "in" function tells me exactly whether the tuple is in the list.

>>> a = [(1,2),(3,4)]

>>> (1,2) in a
True

>>> (1,3) in a
False

That's what I want. But when I do the same thing for b = np.array(a), both give True:

>>> b = np.array(a)

>>> (1,2) in b
True

>>> (1,3) in b
True

So it seems as though the in function for numpy arrays does not check the tuple anymore, but the single values.

1. Why is this?
2. How can I achive a truth request regarding whether a 2d element is in a numpy array as in the example above?