A1. Electrical resistivity is defined a the resistance of a conductor of length 1m and area of cross section 1m sq.. When the length of the wire is doubled, its resistance also doubles (increases), a resistance is directly proportional to length of the wire.
R α l
When its resistance increases, its current decreases, as resistance is inversely proportional to current.
R α 1/I
A2. An ammeter measures electric current. It should have a very low resistance, so that it doesn't change the value of current flowing through the circuit.
*By the way, even I'm a class 10th student.