Wolowitz brings Bernadette by to meet the gang and instantly she takes an interest in Leonard and his work.  When Penny sees how interested she is in her boyfriend's work, she decides to take an interest.  She asks Sheldon to teach her and convinces him he should look at it like an experiement.  Sheldon reluctantly agrees and tries to take her through the 2600 year adventure that is Physics but soon realizes she is kind of hopeless.  Instead, on her request, he teaches her just about Leonard's work.  He ends up giving her a line to recitite to Leonard which basically says how his work is useless and has already been proven by other scientists.

Meanwhile, Wolowitz gets very jealous of Bernadette being so interesting in Leonard's work.  He tries to forbid Leonard, who in turn tells Bernadette, who gets angry at the jealous, possessive Wolowitz and leaves him behind to go to Leonard's to see his work.  Wolowitz, however, is already there to talk to Leonard about not throwing him under the bus next time.  The two have it out until Wolowitz eventually admits it's because he's insecure and they work it out.