A system consists of electrons and protons only. It contains 301 protons and has a total charge of −51e. What is the mass of the system? me=9.11×10^−31kg, mp=1.673×10^−27kg.

When you see distant streetlights through smog, they look dimmer and redder than they do normally. but when you see the same streetlights through fog or falling snow, they look dimmer but not redder. use your knowledge of the interstellar medium to discuss the relative sizes of the particles in smog, fog, and snowstorms compared to the wavelength of light.