Physics Paper 2, Nov/Dec. 2011  
Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
General Comments

Question 5

   State two:
   (a)    differences;
   (b)    similarities
            between thermionic and photoelectric emission.


     Candidates performance in this question was poor.  Most of them could neither state the
     similarities nor the differences between photoeletronic emission and thermionic emission.
    The expected answers are:
     (a)     Differences between thermionic and photoelectric emission

Thermionic emission

Photoelectric emission

-   Caused by heat/themalenergy

-   Electrons are released at a
     particular temperature
-    Time rate of emission of 
     electrons increases with
     increase in temperature

Caused by lightelectromagnetic wave energy
Electrons are released at threshold frequency
 Time rate of emission of electrons increases with/is proportional to increase in intensity

      (b)    Similarities between thermionic and photoelectric emission

  • both are surface phenomena
  • electrons are released in both cases
  • ejected/emitted electrons have kinetic energy.



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