Work function of a metal is the minimum amount of energy required by an electron to just escape from 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 Plank's constant;v₀ is the threshold wavelength and c is the velocity of light in vacuum.
(i) Why different metals has 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 \(h=6.63\times { 10 }^{ -34 }Js;\)\(1eV=1.6\times { 10 }^{ -19 }J\)
(iii) What do you learn from this study?

Radiation has dual nature,i.e., it possesses the properties of both; wave and particle.This prompted de-Broglie to predict dual nature of moving material particles.Thus waves are associated with moving material particles which are called matter waves. The wavelength of matter wave is given by \(\lambda =\frac { h }{ mv } \), where m is the mass, v is the speed of the particle and h is Plank's constant. Read the above paragraph and answer the following questions;
(i) How was the wave nature of the electron established?
(ii) What are the de-Broglie wavelength associated with a particle (i) at rest (ii) moving with infinite speed?
(iii) What are the basic values displayed with this study?

According to Plank's constant quantum theory of light, every source of radiation emits photons(i.e., packets of energy) which travel in all directions with the same speed (i.e., speed of light). Each photon is of energy \(E=hv=\frac { hc }{ \lambda } \) where h is plank's constant, v is the frequency and \(\lambda \) is wavelength of radiation emitted. The photons emitted from different sources of radiation are different.
Read the above passage and answer the following questions:
(i) On what factors does the number of photons emitted per second from a source of radiation depend?
(ii) Why are the high energy photons not visible to eye?
(iii) Which basic values do you learn from this study?

"Know your face beauty through comp[lexion meter" was one of the stall on science exhibition. A student interested to know his/her face beauty was made to stand on a platform and light from a lamp was made to fall on his/her face. The reading of complexion meter indicated the face beauty of the student which might be very fair, fair,semi-fair, semidark dark etc.
(i) What is the basic concept used in the working of complexion meter?
(ii) How is the face beauty recorded by face complexation meter?
(iii) What basic values do you learn from the above study?

The photoelectric effect is a phenomenon of emission of electrons from the surface of a metal when the light of suitable frequency falls on it.
If light of frequency v falls on a photosensitive surface of work function increases or work function then the maximum kinetic energy of photoelectric emitted is given by Einstein's photoelectric equation.
\({ (KE) }_{ max }=\frac { 1 }{ 2 } { { mv }^{ 2 } }_{ max }=hv-{ { \phi }_{ 0 } }\)
The value \({ (KE) }_{ max }\) will increase if the energy of the incident light(hv) increases or work function \({ { \phi }_{ 0 } }\) is decreased.
Read above passage and answer the following questions:
(i) Why can visible light not eject photoelectrons from every metal surface?
(ii) Light of frequency \(7.21\times { 10 }^{ 14 }Hz\) is incident on a metal surface.Electrons with a maximum speed of \(6.0\times { 10 }^{ 5 }{ ms }^{ -1 }\) are ejected from the surface. What is the threshold frequency for photo emission of electrons?\(h=6.63\times { 10 }^{ -34 }Js;\ { m }_{ e }=9.1\times { 10 }^{ -31 }kg\)
(iii) What do you learn basically from the above study?