Physics (Essay) Paper 2 WASSCE (SC), 2021

Question 12

 

(a)        (i)        State the principal factor that determines the relatives stability of    radioactive  nucleus
(ii)        Arrange the following radionuclides in the decreasing order of stability.                            Justify your answer:    ,and
(b)        (i)        Explain the term ionization potential .
(ii)      
             

Observation

 

The diagram above illustrates energy levels in the hydrogen atom. EO is the energy of the ground state.
Part (a):    This question was unpopular among the candidates. Performance was poor.
Part (b):    Performance was poor. Few who attempted failed woefully.
Part (c):    Performance was poor.

The expected answer is:

(a)    (i)         Principal Factor that Determines the Relative Stability of a Radioactive Nucleus

                        Neutron-proton ratio.                                                                         

 

                     (ii)        Arrangement of Radio Nuclides in Decreasing Order of Stability

      

                                

                                        
Decreasing order of stability

                                 , ,                                     

         (b)        (i)         Ionization potential

The minimum energy required to remove an electron completely from an atom     

                     (ii)        (I)        Calculation of Eo

                                               OR                                                 

                                                       

                                              = -13.6 eV                                                             

                                 (II)       Calculation of Ionization Potential

                                             Ionization Energy =                                                

                                                                           =
= 13.6 eV                        

                                             Therefore, Ionization potential = 13.6 eV     

         (c)        (i)         Explanation of the Statement

The minimum energy needed to remove an electron from the surface of sodium metal is 2.0 eV.                                                                 

            (ii)        For sodium metal,
= 2.0 x 1.6 x 10-19 J

                                 

                                  

                                        = 6.2 x 10-7 m                     

                                    160nm = 160 x 10-9

                                                                = 1.6 x 10-7 m             
Since 1.6 x 10-7 m is less than 6.2 x 10-7 m, photoelectrons would be emitted when light of 160 nm is shone on the metal surface