A scanning tunneling microscope (STM) can precisely determine the depths of surface features because the current through its tip is very sensitive to differences in the width of the gap between the tip and the sample surface. Assume the electron wave function falls off exponentially in this direction with a decay length of $0.100 \mathrm{~nm}$, that is, with $C=10.0 / \mathrm{nm}$. Determine the ratio of the current when the STM tip is $0.500 \mathrm{~nm}$ above a surface feature to the current when the tip is $0.515 \mathrm{~nm}$ above the surface.