Answer
See answers.
Work Step by Step
a. Outside of a uniformly-charged sphere, the electric field is the same as if all the charge were concentrated at the center of the sphere. According to Example 16–6, a toner particle carries the charge $Q_T$ of 20 electrons. Let N be the number of toner particles.
$$E=\frac{kQ}{r^2}=\frac{kNQ_T}{r^2}$$
$$N=\frac{Er^2}{kQ_T}=\frac{(5000N/C)(0.50m)^2}{(8.988\times10^{9}(N \cdot m^2)/C^2)(20)(1.6\times 10^{-19}C)}\approx 4\times10^{10}$$
b. Example 16–6 states that a toner particle has a mass of $9.0\times10^{-16}kg$. The total mass is the number of particles multiplied by the mass of one particle.
$$M=Nm_T=(4.346\times10^{10})(9.0\times10^{-16}kg)=4\times10^{-5}kg$$
