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if light of wavelength lambda falls on a metallic sphere of radius R,maximum charge acquired by the sphere will be????

if light of wavelength lambda falls on a metallic sphere of radius R,maximum charge acquired by the sphere will be????

Grade:

4 Answers

pavani suhani
6 Points
9 years ago

when the electrons are ejected from the surface of the sphere, it becomes positively charged.there will an extra attractive force on the photo electrons  due to the acquired charge.if the potential of the sphere is raised to Vthen 

 

( hc/λ)-(hc/λo)=e(Q/4πεR)

                                   where Q is the charge acquired by the sphere

Arka Sarkar
4 Points
9 years ago

but lambda not is not given in the option...

Ramesh Babu Gattu
19 Points
9 years ago

dear arka,

first we assume that the work function of the metal < h x frequency of the light incident.

now, sure, the electrons (photoelectrons) are emitted with some energy. But, over a period of time, the metal is not positively charged due to removal of electrons as the stray electrons in the medium (air, eventhough when an ultra high vacuum is creately)are sufficient in number to neutralize the metal.

hence, over some time, the metal is electrically neutral only.

Ramesh Babu Gattu
19 Points
9 years ago

there was an answer by someone else using coulombs law, but the electron is emitted only after satisfing the condition, that input energy of the light is greater than the work function of the metal (which takes care of all the attractive forces in making the electron binded to the metal surface). if this is excess, then only electron comes out, else there is no photoemission. and let me tell you, this is modern physics with probability theory. which electron will come out is uncertain!!!!!

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