The electric current is defined as the charge Q that passes a certain point in a time [tex]\Delta t[/tex]:
[tex]I= \frac{Q}{\Delta t} [/tex]
We know the current, [tex]I=106 \mu A=106 \cdot 10^{-6} A[/tex], and the time, [tex]\Delta t=17.0 s[/tex], so the total charge that strikes the target during this time is
[tex]Q=I \Delta t=(106 \cdot 10^{-6}A)(17.0s)=1.8 \cdot 10^{-3}C[/tex]
To find the number of proton, we must divide the total charge by the charge of a single proton, which is [tex]q=1.6 \cdot 10^{-19}C[/tex]:
[tex]N= \frac{Q}{q}= \frac{1.8 \cdot 10^{-3}C}{1.6 \cdot 10^{-19}C}=1.13 \cdot 10^{16} [/tex]
And this is the number of protons that strike the target in 17.0 s.
