2 A proton beam in an accelerator carries a current of $125\U{$\mu$A}$
3 If the beam is incident on a target, how many protons strike the
4 target in a period of $23.0\U{s}$.
8 Current is defined as $I\equiv\deriv{t}{Q}$. Therefore, strike rate is
10 \deriv{t}{N} = \deriv{t}{Q} \cdot \frac{1\U{proton}}{q} = \frac{I}{q} \;,
12 where $q=1.60\E{-19}\U{C}$ is the charge of a single proton. The
13 number of strikes in the allotted time is thus
15 \Delta N = \deriv{t}{N} \cdot \Delta t = \frac{I\Delta t}{q}
16 = \ans{18.0\E{15}\U{protons} = 18.0\U{petaprotons}} \;.