Work function of a metal is the maximum amount of energy required by an electron, to just escape form the metal surface without any kinetic energy. The expression for work function of metal is `phi_(0)=hv_(0)=hc//lambda_(0)`, where h is Planck's constant, `v_(0)` is the threshold frequency, `lambda_(0)` is the threshold wavelength and c is the velocity of light in vacuume. Read the above paragraph and answer the following questions:
(i) Why different metals have different work function?
(ii) What is the threshold wavelength of the incident radiation for a metal surface whose work function is `1.2 eV. Given h=6.63xx10^(-34)Js, 1eV=1.6xx10^(-19)J`.
(iii) What do you learn from this study?

Explanation

(i) Work function of a metal depends upon the amount of restraining forces acting on the electrons to be ejected. In different metals, the amount of restraning forces on the electrons to be ejected is different. Hence, work function for different metal is different.
(ii) Here, `phi_(0)=1.2eV=1.2xx1.6xx10^(-19)J`
As, `phi_(0)=(hc)/(lambda_(0)) or lambda_(0)=(hc)/(phi_(0))=((6.63xx10^(-34))xx(3xx10^(8)))/(1.2xx1.6xx10^(-19))=1037xx10^(-9)m=1037nm`
(iii) Work function of a metal refers to the minimum energy required by an electron escape from the metal. In day to day life, we find that we can purchase sometimes only when we have money, which is atleast equal to or more than that price. Thus to purchase comforts of life, we have to work hard and earn money by fairs means.