Question

Imagine shooting various colors of light at different kinds of metals. Depending on the work function of each metal, the light will or will not have enough energy to knock of an electron. (a) Which of the following metals will NOT emit electrons when visible light (with wavelengths of 380 nmto 700 nm) shines on them? (b) If visible light can cause the metal to emit electrons, specific if electrons will be emitted when red (685 nm) light is used, green (532 nm) light is used and blue (473 nm) light is used. W0 is the work function for each metal. Cesium(W0= 2.1 eV) Rubidium(W0 = 2.3 eV)

Answer 1

From photoelectric equation is  

E = W0 + k.e

E is energy given to the electron and W0 is fowrk function of the metal surface , k.e is kinetic energy of emitted electron

here if the energy given is greater than the work function then the electrons will emit otherwise not

from the equation E = h*nue = h*c/lambda

h is plnck's constant = 6.626*10^-34 J.s , c is speed of light c= 3*10^8 m/s

Cesium(W0= 2.1 eV)

for the red light of wavelength lambda = 685 nm  

E = (6.626*10^-34*3*10^8)/(685*10^-9) J = 2.902*10^-19 J = 1.814 eV

E is less than W0 so the electrons will notemit

for the green light of wavelength lambda = 532 nm  

E = (6.626*10^-34*3*10^8)/(532*10^-9) J = 3.736*10^-19 J = 2.34 eV

E is greater than W0 so the electrons will emit

for the blue light of wavelength lambda = 532 nm  

E = (6.626*10^-34*3*10^8)/(473*10^-9) J = 4.20*10^-19 J = 2.625 eV

E is greater than W0 so the electrons will emit

---------------------

Rubidium(W0 = 2.3 eV)

for the red light of wavelength lambda = 685 nm  

E = (6.626*10^-34*3*10^8)/(685*10^-9) J = 2.902*10^-19 J = 1.814 eV

E is less than W0 so the electrons will notemit

for the green light of wavelength lambda = 532 nm  

E = (6.626*10^-34*3*10^8)/(532*10^-9) J = 3.736*10^-19 J = 2.34 eV

E is greater than W0 so the electrons will emit

for the blue light of wavelength lambda = 532 nm  

E = (6.626*10^-34*3*10^8)/(473*10^-9) J = 4.20*10^-19 J = 2.625 eV

E is greater than W0 so the electrons will emit