I find quantum mechanics to be very hard, and I am currently having trobule with the following 2 problems, can someone please help me out? 1) A thin solid barrier in the xy-plane has a 10-micrometer-diameter circular hole. An electron traveling in the z-direction with vx=0 m/s passes through the hole. Afterward, is vx still zero? If not, within what range is vx likely to be? My textbook says that the uncertainty principle is (delta x)(delta px) > h/2 But I am not sure what delta x would be in this situation...and I got completely confused with the x,y,z direction business as well...if vx is zero originally, why would it possibly be different after going through the hole? I don't understand what is going on... 2) A typical electron in a piece of metallic sodium has energy -Eo compared to a free electron, where Eo is the 2.7 eV work function of sodium. At what distance beyond the surface of the metal is the electron's probability density 10% of its value at the surface? First of all, I don't get what it means by saying that the elctron has energy "-Eo compared to a free electron", what is the energy of a free electron? why is there a negative sign in front of Eo? Secondly, I don't even know which equation to use, can someone give me some hints on solving this problem? I am totally lost... Any help is greatly appreciated!