waecE-LEARNING
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
Weakness/Remedies
Strength
















Question 7

  The table shows the pointer reading of a spring balance when different weights are hung on it.
Determine the value of F.


Weight/N

5

10

F

Pointer reading/cm

8

12

30

 

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comments

     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 temMany candidates attempted this question and majority of them faired very well in it.

 

The expected answer is:
.         F  =  ke
            10 – 5  =  k(12 – 8)                        ……..(A)                         
            F – 10  =  k(30 – 12)                      ……..(B)                        
            Solving simultaneously equations   (A) and (B)

              F  =  32 . 5N

perature
-    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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