A device called a photocell detects light by letting it fall onto a metal and then measuring the current from the ejected electrons. You are designing a photocell to work with visible light and are considering the use of either aluminum (work function = 4.3 eV) or cesium (work function = 2.1 eV). 

(a) Which one is a better choice? 

(b) What is the lowest photon frequency that can be detected with your photocell? 

(c) Where does this frequency fall in the electromagnetic spectrum?