In an experiment to measure the charge to mass ratio e/m of the electron by Thomson's method, the values of the deflecting electric field and the accelerating potential are 610 N/C (newton per coulomb) and 150V, respectively. The magnitude of the magnetic field that leads to zero deflection of the electron beam is closest to (a) 0.6T (b) 1.2T (c) 0.4T (d) 0.8T