Photoelectric Effect question.

[guncamp]

I am reading a book on an introduction to quantum physics and I came across what appears to me as two conflicting statements. I believe it said that a single photon cannot have enough energy to knock loose an electron due to the fact the the photon is quantized. Yet a few pages after this the book claims that "The energy necessary to knock loose an electron is provided by a single photon in an incoming electromagnetic wave".

 

So which statement is true?

Edited May 10, 2013 by guncamp

[krash661]

it appears the problem is that you think a proton and photon are the same particle,
but i'm not sure,

Proton
http://en.wikipedia.org/wiki/Proton

Electron
http://en.wikipedia.org/wiki/Electron

photon
http://en.wikipedia.org/wiki/Photon

Photoelectric effect
http://en.wikipedia.org/wiki/Photoelectric_effect

Edited May 10, 2013 by krash661

[swansont]

I am reading a book on an introduction to quantum physics and I came across what appears to me as two conflicting statements. I believe it said that a single photon cannot have enough energy to knock loose an electron due to the fact the the photon is quantized. Yet a few pages after this the book claims that "The energy necessary to knock loose an electron is provided by a single proton in an incoming electromagnetic wave".

 

So which statement is true?

 

I believe you misread it. A single photon below a certain frequency (or above a certain wavelength) can't cause ionization. e.g. a red photon has around 1.5 eV of energy, and will not cause ionization. But a blue photon has double that, and can cause ionization in some molecules. A UV photon can ionize almost any molecule and many atoms.

[guncamp]

My apologies, I for some reason put proton instead of photon. i corrected the mistake.

[krash661]

read what swansnot wrote and that image i posted ,

[guncamp]

I believe you misread it. A single photon below a certain frequency (or above a certain wavelength) can't cause ionization. e.g. a red photon has around 1.5 eV of energy, and will not cause ionization. But a blue photon has double that, and can cause ionization in some molecules. A UV photon can ionize almost any molecule and many atoms.

I must have misread it. Looking back it indeed does say photons of small energy. Silly mistake, I must have just overlooked it. Thanks for the clarification.