If You Want to Design a Phototube That Ignores All $1.77 \mathrm{eV}$

Multiple Choice

If you want to design a phototube that ignores all visible light, what should its cathode's work function be?

A) Below $1.77 \mathrm{eV}$
B) Any value between $1.77 \mathrm{eV}$ and $3.1 \mathrm{eV}$
C) Some specific value between $1.77 \mathrm{eV}$ and $3.1 \mathrm{eV}$
D) Above $3.1 \mathrm{eV}$
E) Some other value or range (specify)