What is the energy of a photon & what potential difference must electrons be?

[Vertrex]

Homework Statement

a) What is the energy of a photon that has a wavelength of 0.10 μm?
b) Through approximately what potential difference must electrons be accelerated so that they will exhibit wave nature in passing through an aperture 0.10 μm in diameter?

The Attempt at a Solution

I've already done part (a) but I'm having trouble understanding whether I should take the diameter of that aperture as the wavelength in part (b).

 

[DiracRules]

When does an electron show its wavelike behaviour? This is the key for (b).