in topic test 2,Q.1] A ball of mass 0.5 mg carrying a charge of 4*10-8 C hangs from a thread, making an angle of 30o with the vertical, near a large conducting plate. Determine the surface charge density of the plate.
In ans. it is gven that :
W=mg=(0.5*10-6)*9.8 N
But m =10-3 & M=10-6
Then how in the ans. it is given 10-6
please explain as soon as possible.