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Physics Paper 2, Nov/Dec. 2009  
Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
General Comments

Question 13
Part II:      Candidates were required to answer any five questions from this part.
  1. Explain the term overtone as applied to a musical note.
  1. A travelling wave has a frequency of 20 Hz and wavelength 1.2m. 

Calculate the time it will take the wave to reach a point 96 m from its source.

  1. (i)   Draw and label a ray diagram to illustrate the arrangement of an instrument

that can be used to produce an enlarged view of a tiny object on a screen.
(ii)  Name the instrument in (c)(i).

  1. An object of height 0.02 m is to be enlarged on a screen to a height of 0.8 m by

means of a converging lens placed 4.0 m from the screen.  Calculate the:

    1. distance of the object from the lens;
    2. focal length of the lens.




Part (a) though a popular question but appeared not to be properly taught in schools because it was poorly attempted by most candidates.

Part (b) was fairly well attempted.

In part (c), the drawing of a projector/projection lantern proved difficult to many candidates.  Performance was poor in this part.  Part (d) was well fairly attempted.

The expected answers were as follows:         

(a)        Overtones are integral multiples of fundamental frequency emitted by a musical
Valid additional information   e.g. the first overtone is the second harmonic.                                                                 
(b)        f  =  20Hz   λ  =  1.2
             V  =  f λ                                                                                                                      
              =  20  x 1.2                                                                                                   
              =  24 ms-1                                                                                                                 

            But V  =  x/t                                                                                                                  

            24  = 96/t                                                                                                                      
            t  =  96/24  =   4 seconds                                                                                            
  (c)(i) Diagram

Converging lens

½  will be deducted if:
-  u > v,
-  no arrow shown
Note:  if a projector lantern is not drawn in full and if candidates show lens,
object, screen and rays, score accordingly.

     (ii)   Instrument is projector or projection lantern                                                                

(d) (i)   M  = Hi
=   0.8   =  40                                                                                                                
            U  = V   =   4   =  0.1m                                                              
                  40  =  40                                                                                                                         

     (ii)    1  +  1  =  1
              U     V      f

 1   +   1  =  1
0.1      4       f

f  =  0.0975m       
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