Photomultiplier Tube

For each secondary electron that hits the scintillator, a photon that has a wavelength of 4.00 × 10^-7 m is produced. This photon hits the photocathode, which has a work function of 1.80 eV, and initiates an electron cascade.

Inside the photomultiplier tube are several dynodes (intermediate anodes) and a final collector anode. Each dynode is kept at a greater positive potential than the one previous to it. The electric potential difference between one dynode and the next is 150 V.

A particular electron, as it leaves one dynode, has a kinetic energy of 1.00 × 10–17 J. The speed of this electron when it reaches the next dynode will be
A. 5.93 × 10^6 m/s
B. 7.26 × 10^6 m/s
C. 8.64 × 10^6 m/s
D. 1.32 × 10^7 m/s