whats the differences in magnitudes of the sun and sirius?

Answer 1

Since your question title deals with apparent magnitudes, I will assume that is the type for which you want the difference between sun and Sirius (the apparent-brightest star other than the sun). The sun's apparent brightness is much higher, and its apparent magnitude accordingly much lower, than Sirius becasue it is so much closer. Lower magnitude numbers correspond to higher brightness, because of some convention adopted centuries ago.

The sun's apparent magnitude is -26.7 and that of Sirius is -1.5. That difference of nearly 25 magnitudes corresponds to a factor of 10^10 in received radiation, since each 5 magnitudes is a factor of 100.