two seperate monochromatic light beams A and B of the same intensity are falling normally on a unit area of a metallic surface. their wavelengths are λa and λb respectively. assuming that all incident light is used in ejecting the photoelectrons,the ratio of the number of photoelectrons from the beam A to that from B is?

Question

two seperate monochromatic light beams A and B of the same intensity are falling normally on a unit area of a metallic surface. their wavelengths are  λa and  λb respectively. assuming that all incident light is used in ejecting the photoelectrons,the ratio of the number of photoelectrons from the beam A to that from B is?

yrelhan4 · Answer

@Mashy @shubhamsrg

anonymous · Answer

Number of photo electrons depends on what? (what property of the incident light?)

yrelhan4 · Answer

intensity.

anonymous · Answer

good.. now read the first line of your question carefully :D

yrelhan4 · Answer

i get your point. but the answer is  λa/ λb

anonymous · Answer

what? :O.. thats preposterous ! 
wavelength only decides the kinetic energy of the electrons and not the number! :-/

anonymous · Answer

that is so stupid.. and if lambda a is above the threshold wavelength, there ain't gonna be no photoelectrons :P..

anonymous · Answer

that answer is 100 percent wrong!

anonymous · Answer

either that or i don't have a 100 percent understanding in photoelectric effect :P

yrelhan4 · Answer

well this is a question from roorkee 1990, so i dont think it can be wrong. just think about it and tell me if you get it.

anonymous · Answer

they could have given the answer wrong in your book.. the question is def right.. and the answer should be 1:1.. but lemme think mor!

yrelhan4 · Answer

1:1 is not in the options.

anonymous · Answer

Ok.. the number of electrons = the no of photons
Since the intensity is same, energy per second is same.. 

so use E = nhf .. for each one..  n = no of photons!

anonymous · Answer

what?? that should give you the answer!

yrelhan4 · Answer

hmm. but you did this just to get the answer? if 1:1 was an option, it would be your first choice?

anonymous · Answer

yea and that's wrong. i understand how
you see.. photoelectron's directly proportional to intensity.. thats true.. it only says if you double the intensity , photoelectrons double.. only reason is because photon no.s double. .

however.. it need not necessarily mean that two light source of different intensities should have same no. of photons.. and hence give same photo electrons :D.. thanks! i learnt something :D

yrelhan4 · Answer

haha. i had to read it a few of times before i could get it. thank you! :)

anonymous · Answer

yea.. m very lazy to type properly these days :D.. ok i gotta go for lunch now bye!

yrelhan4 · Answer

i wish you could take my exams. :P

yrelhan4 · Answer

bye.

shubhamsrg · Answer

final ans is lambda(a)/lambda(b) right ?

yrelhan4 · Answer

yup