A rod of mass m and length 2l is connected to two massless strings as shown in figure. A wooden disk of same mass m is fixed at the mid - point of the rod in such a way that the plane of disk is perpendicular to the rod. A massless wire is wrapped around disk and having current I . There is vertically upward magnetic field B at the location of disk . ( sense of current in the loop when seen from string P side is clockwise)

The tension in the string P is

Options

A. `mg+(I pi R^(2)B)/(2l)`
B. `mg-(I pi R^(2)B)/(2l)`
C. mg
D. 2mg

Answer

A