Electrons and Photons
7. Which metals are suitable for
photoelectric effect? Why?
Ans: The metals (generally alkali
metals) which have low work function are suitable for photoelectric ef
fect. As
work function of a metal is the minimum amount of energy required to eject an
electron from the surface of the metal (without imparting any kinetic energy),
so electrons can be ejected from such metals even by less energetic radiation
(i.e. visible light).
8. Why does electric discharge
take place at low pressure and high potential difference?
Ans: At low pressure and high
potential difference, mean free path for the charged particles increased and
they acquire sufficient kinetic energy to produce ionization. More ions and
electrons are produced in the gas due to collisions. The electrons move towards
the anode and the positive ions move towards the cathode. Hence, electric
discharge takes place through the gas.
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