Physics Paper 2, MAy/June. 2013  
Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main

General Comments

Question 13



Part (a)  This part was very popular  among the candidates and the first section was correctly answered however the explanation was poorly handled.
Part (b)   Most candidates were busy explaining why megaphones magnify sound rather than explaining why they were shaped like funnel.  This part was poorly handled.
Part (c)   A good number of the candidates got reasonable score as they were able to identify the angles correctly.  Very few candidates however mistook 30o as the angle of incidence.  Some candidates left out the arrows in their diagram.  Majority stated the correct formular but substituted wrongly i.e 1.5 = sin30
                                                                                                            sin r
              Instead of 1.5  =  sin60
                                          sin r
Part (d).  This part was not well attempted.  Some forget to square the angular speed
                i.e they wrote a= r instead of a = 2 r.
               Some could not convert correctly cm to m
 The expected answers are:
       (a)   Sound wave travel(s) faster on a hot day                                                                  
Speed of sound is proportional to the square root of absolute temperature, v α 
Hence the higher the temperature the greater the speed of sound
      (b)     Intensity of sound is energy per second per unit area. Hence sound produced has greater intensity before spreading out through the larger segment of the cone  
               At the smaller end of the cone, the sound energy comes into contact with a small mass of air . As it comes out of the larger open end, the energy sets a larger mass of air into vibration, hence the final sound is louder.
       (c)(i)              For copying the diagram                     award        

              •   X correctly shown          
              •    Y correctly shown         
              •   Z correctly shown            

  (ii)         n   =                                                                                                         
                                1.5  =                                                                                                 
                                  =  Sin-1(Sin 60)
                                     =   Sin-1   0.5774
                                     =     35o                                                                                                                                                                   
      (d)         a   =   ω2 r ;      ω = 2                                                                                      
                        =   (22r                                                                                                    
  =  (2 x 22 x f)2 x  1.0
                                           7               100                                                                                                        
                                              =       50.0 Hz                                                                      


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