figure out electrons when traveling through a graphine sheet. >> these characters want to be included. and then there's the very beautiful penny who lives across the hall from sheldon and leonard. >> welcome to the building. >> oh, thank you. maybe we can have coffee some time. >> great. >> great. >> great. [ laughter ] >> she's funny, but they show her as having a fraction of their iq. >> cal tech department of applied physics. you may be familiar with some of my work. it's currently orbiting jupiter's largest moon taking high-resolution digital photographs. >> penny. i work at the cheesecake factory. >> but then they bring in bernadette and amy. >> hello. >> she eventually became sheldon's love interest, and of course that opened up a whole