Answer
$5.3\times10^{-17}T$
Work Step by Step
Model the proton beam as a current I, equal to the rate at which protons pass, multiplied by the charge of a single proton. Use equation 20–6.
$$B=\frac{\mu_oI}{2\pi r}$$
$$=\frac{(4\pi \times10^{-7} T\cdot m/A)(2.5\times10^9p/s)(1.60\times10^{-19}C/p)}{2\pi (1.5m)}$$
$$=5.3\times10^{-17}T$$
