hi every body

i hope any 1 feel like what i am feeling now .. specially when i received my quiz mark .. i was surprised about the way of correcting ..

the main point is that i was confident about the answer of question 3 .. but the doctor said it is wrong .. he said i should use the relation between the number of electrons (N) to the volume (V) to get the density of charge(n) .. Even we learned that this relation used only in 3 dimensions and the question was about potential barrier which is one dimension which means that N=2n and n is fermi level and N is the number of conduction electrons .. am really con fused