Cesium is used extensively in photocells and in television cameras because it ha
ID: 2048641 • Letter: C
Question
Cesium is used extensively in photocells and in television cameras because it has the lower ionization energy of all the stable elements.What is the maximum kinetic energy of a photoelectron ejected from cesium by 555nm light? Note that if the wavelength of the light used to irradicate the cesium surface becomes longer than 660nm, no photoelectrons are emitted.
I tried figuring this out by setting it as (6.6254x10^-34J/s)(3x10^8m/s)/(555nmx10^-9), and it's wrong according to the back of the book, since the answer is supposed to be 6.02x10^-20J.
Explanation / Answer
The answer would be the difference between the energy of a 555 nm photon and 660 nm photon, since the 660 nm photon establishes the work function of Cs.
E = hc/ so we want
hc/555 nm - hc/660 nm
= (6.626 * 10-34 J-s)(2.9979 * 108 m/s)(1/555 * 10-9 m - 1/660 * 10-9 m)
= 5.69 * 10-20 J which is not your book answer .
To get your book answer, the photon for which the photoelectrons are no longer emitted would have to have a wavelength of 667 or 668 nm. Are you sure you copied the 660 nm correctly?