Kinetic energy of electron,
∴ speed of electron,
Since the velocity (Vector v) of the electron makes an angle of θ = 60º with the magnetic field Vector B, the path will be a helix. So, the particle will hit S if
GS = nP Here n = 1, 2, 3, .........
But for B to be minimum, n = 1
Substituting the values, we have