# What is the difference between the photoelectric effect and secondary emission?

What is the difference between photoelectric effect and secondary emission in photo multiplier tubes? In other words, why the difference between the energy of the incident photon and the work function of the material (in photoelectric effect) turns into kinetic energy to the released electron, while this is not the case in secondary emission ?

• Did you read the Wikipedia articles I just linked in your question? – ACuriousMind Apr 7 '15 at 14:27
• Yes ,sir I have already went through all that stuff but I did not find a clear distinction between the two effects. Thanks anyway. – Mohamed Goda Apr 7 '15 at 16:15
• Well, what is the result of applying conservation of momentum when a primary electron generates (several) electrons at the next plate? – Carl Witthoft Apr 7 '15 at 18:35
• Carl,My question is why several electrons are released per one incident electron? why it is not one-to-one correspondence like that in photoelectric effect? – Mohamed Goda Apr 7 '15 at 22:18

The difference you are looking for is in the particle energy. The photon energy for visible light is about $3\,\mathrm{eV}$ (electron-volt), just enough to kick one electron from photocathode. In the photomultiplier, this electron is accelerated towards dynodes with high voltage. If it is $1000\,\mathrm{V}$, then the electron gains kinetic energy of $1000\,\mathrm{eV}$, thus being able to release much more secondary electrons on impact.