Suppose the fractional efficiency of a metal surface with work function 1.40 ev is 1.0 × 10-18; that is, on average one electron is ejected for every 1018 photons that reach the surface. what would be the current of electrons ejected from such a surface if it were illuminated with 510 nm light from a 1.75 mw laser and all the ejected electrons took part in the charge flow?

Two identical stars with mass m orbit around their center of mass. each orbit is circular and has radius r, so that the two stars are always on opposite sides of the circle. (a) find the gravitational force of one star on the other. (b) find the orbital speed of each star and the period of the orbit. (c) how much energy would be required to separate the two stars to infinity?