Video Transcript
A neutron has a charge of zero
coulombs and a mass of 1.67 times 10 to the negative 27th kilograms. What is the charge-to-mass ratio of
a neutron?
Given the charge and mass of some
object, in this case a neutron, its charge-to-mass ratio is simply its charge
divided by its mass. In symbols, we’d write the
charge-to-mass ratio as capital 𝑄 divided by 𝑚, where capital 𝑄 is the charge and
𝑚 is the mass. The units of this quantity are
whatever units we use for charge divided by whatever units we use for mass. For this particular question, the
calculation is quite easy because the neutron has a charge of zero and a mass that
is not zero. Therefore, when we divide charge by
mass, we have zero divided by a number that isn’t zero, the result of which is just
zero. Carrying over the units, this gives
us a charge-to-mass ratio of zero coulombs per kilogram. A charge-to-mass ratio with a
numerical value of zero is characteristic of all neutral particles with nonzero
mass, like the neutron. Particles like the photon that are
neutral but also have zero mass do not have a well-defined charge-to-mass ratio.
