See image. Show all steps. Certain metals and alloys (mixtures of compounds of t
ID: 1035539 • Letter: S
Question
See image. Show all steps.
Certain metals and alloys (mixtures of compounds of two or more metals) have unusually low work functions and are useful as photocathodes (surfaces yielding photoelectrons) Light of wavelength 389 nm shines on a particular "trialkali" photocathode, and electrons of maximum kinetic energy 1.45 eV are given off. a) b) c) d) What is the work function W (in electron-volts and joules) of the surface? What is the minimum de Broglie wavelength of the ejected photoelectron? What maximum wavelength of light will cause photoemission from this cathode? When a pulsed laser at 389nm carrying 1.25 mJ per pulse is used, how many electrons are ejected per pulse of this 1.25 mJ laser? When a pulsed laser at 800nm carrying 1.25 mJ per pulse is used, how many electrons are ejected per pulse of this 1.25 mJ laser? e)Explanation / Answer
a) Energy of the incoming electrons = 1240/lambda(in nm)
=> 1240/389
=> 3.1876 eV
Work Function = Energy of the incoming electrons - Kinetic energy
Work Function = 3.1876 eV - 1.45eV = 1.7376 eV
b) For part b, we need to use the above formula and equate it to work function value
1240/lambda (in nm) = 1.7376
lambda (in nm) = 713.627 nm
c) Kinetic energy for 389 nm = 1.45 eV
Number of electrons in pulse = Energy/Kinetic energy of one electron
=> 1.25 * 10^(-3) J/ 1.45 * 1.6 * 10^(-19)
=> 5.387 * 10^(15) electrons
d) Zero, since the wavelength is higher than the wavlength calculated in part b, hence there will be no ejection from the surface