S=2,5 mm² = 0,0000025 m²
j=100 A/m²
[tex]j=\frac{I}{S} \ \ \rightarrow \ \ I=j*S=100 \ [\frac{A}{m^2}]*0,0000025 \ [m^2]=0,00025 \ A=0,25 \ mA=250 \ \mu A[/tex]
t=20 ms=0,02 s
[tex]I=\frac{Q}{t} \ \ \rightarrow \ \ Q=I*t=0,00025 \ [A]*0,02 \ [s]=0,000005 \ C=5 \mu C[/tex]
