Problems are listed in approximate order of difficulty. A single dot (•) indicates straigh...

Problems are listed in approximate order of difficulty. A single dot (•) indicates straightforward problems involving just one main concept and sometimes requiring no more than substitution of numbers in the appropriate formula. Two dots (••) identify problems that are slightly more challenging and usually involve more than one concept. Three dots (•••) indicate problems that are distinctly more challenging, either because they are intrinsically difficult or involve lengthy calculations. Needless to say, these distinctions are hard to draw and are only approximate.

••• Derivation of the field-emission equation. Show that the tunneling current in field emission is given by , where E is the electric field. This is a difficult problem because the tunneling barrier does not have constant height. See Section 17.10 for direction in how to deal with this kind of tunneling problem.