7) 300

Let number of turns on primary coil be = N1 = 1500
Let number of turns on secondary coil be = N2
Input voltage = V1 = 250V
Output voltage = V2 = P/I = (0.5×1000)/10 = 50 V

Formula:

N1 = N2
V1    V2

1500 = N2
 250     50

N2 = 300