An isotropic point source produces light at wavelength 470 nm, at the rate of 170 W. A light detector is placed 390 m from the source. Determine the maximum rate dB/dt at which the magnetic component of the light modifies with time at the detector's position? The speed of light is c = 3 × 108 m/s, and µ0 = 4p × 10-7 H/m.