Four infinitely long wires lie in the same plane and intersect to form a square with side length l = 35 cm. Two of the wires point up the page, with the one on the left carrying i1 = 4.0 A upward and the one on the right carrying i2 = 3.0 A downward. The other two wires point across the page, with the one on top carrying i3 = 5.5 A to the right and the one on the bottom carrying i4 = 1.5 A to the right. A proton is travelling through this region of space, and at the moment it crosses the centre of this square it has a velocity of v = 6.0 km/s to the right. What is the magnitude of its acceleration 'a' at this moment? For the limits check, investigate what happens to a if the square gets very large (l ).