Question

There is a naturally occurring vertical electric field near the Earth’s surface that points toward the ground. In fair weather conditions, in an open field, the strength of this electric field is 110.0 N/C$110.0\text{ N/C}$ . A spherical pollen grain with a radius of 15.0 μm$15.0\text{ μm}$ is released from its parent plant by a light breeze, giving it a net charge of −0.700 fC$-0.700\text{ fC}$ (where 1 fC=1×10−15 C$1\text{ fC}=1\times {10}^{-15}\text{ C}$). What is the ratio of the magnitudes of the electric force to the gravitational force, ?electric/?grav$F_{\mathrm{e}\mathrm{l}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{r}\mathrm{i}\mathrm{c}}/F_{\mathrm{g}\mathrm{r}\mathrm{a}\mathrm{v}}$ , acting on the pollen? Pollen is primarily water, so assume that its volume mass density is 1000 kg/m3$1000\mathrm{k}\mathrm{g}/{\mathrm{m}}^3$ , identical to the volume mass density of water.