The Figure Shown Depicts the Cross Section of a Current

The figure shown depicts the cross section of a current carrying ring of wire having a radius of 4 cm.A 1-A current flows in the ring in the direction indicated in the drawing.The ring is free to rotate,clockwise or counterclockwise,about an axis normal to the page which passes through its center.The ring is connected to a spring with a spring constant of 100 N/m as shown.The spring is fixed to a wall at the other end.When the ring is in the vertical position,the spring is at its natural length.One may assume that the length of the spring is long enough such that any extension or compression follows Hooke's law.Determine the magnitude of the change in length of the spring when a magnetic field B = 2 T is applied along the vertical axis.

A) 1.25 mm
B) 5.0 mm
C) 2.5 mm
D) 6.26 mm