Answer
$0.47mT$
Work Step by Step
We know that
$v=\sqrt{\frac{2e\Delta V}{m}}$
We plug in the known values to obtain:
$v=\sqrt{\frac{2(1.6\times 10^{-19})(550)}{9.11\times 10^{-31}}}$
$v=1.4\times 10^7\frac{m}{s}$
Now we can find the magnitude of the magnetic field as
$B=\frac{mv}{er}$
We plug in the known values to obtain:
$B=\frac{9.11\times 10^{-31}(1.4\times 10^7)}{(1.6\times 10^{-19})(0.17)}$
$B=4.7\times 10^{-4}T=0.47mT$
