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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
Weakness/Remedies
Strength












Question 10
Part I:      Candidates were required to answer any five questions from this part.

Electrons from a hot cathode are accelerated from rest onto a target in a vacuum tube maintained at a potential difference of 180 volts.  Calculate the velocity of the electrons on reaching the target.
[Mass of electron = 9.0 x 10-31 kg; charge of an electron = 1.6 x 10-19 C].

_____________________________________________________________________________________________________
Observation

This was attempted by few candidates and the performance was fair.  The expected answer is:
           
Let the velocity of the electron at the target be u

            ½ mu2  =  e V

or         u2  =  2eV
                        m                                                                                                            

       =   2 x 1 . 6  x 10-19  x 180
                        9.0 x 10-31                                                                                               
               
  u   =   8  x 106 ms‑1

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