If you want to design a phototube that is able to respond to all visible light wavelengths, 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)

Question

Quizplus · Accepted Answer

The work function of the cathode must be below $1.77 \mathrm{eV}$ to respond to all visible light wavelengths, as $1.77 \mathrm{eV}$ corresponds to the energy of the red edge of the visible spectrum (around 700 nm), and lower work function values allow the cathode to be sensitive to even lower energy (longer wavelength) light.

If You Want to Design a Phototube That Is Able 1.77eV1.77 \mathrm{eV}1.77eV

If You Want to Design a Phototube That Is Able $1.77 \mathrm{eV}$