Physics Paper 2, Nov/Dec. 2012
 Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
Weakness/Reme1ies
Strength

Question 15

(       Question 15

1.   Explain radioactivity under the following headings:
2.  meaning;
3.  types.

1.  State two:
2.  advantages of nuclear fusion over nuclear fission;
3. methods of detection of radioactivity.
1.   A nuclear fusion equation for generation of power is shown below

+                              +
[  H = 1.00728u;  H = 2.00141u He = 3.00160u He = 4.00150u;
c  = 3.0 x 108 ms-1; Iu = 1.7 x 10-27 kg]

1.   An electron of mass 9.1 x 10-31 kg moves with a speed of 4.8 x 108 ms-1 in a   vacuum.  Calculate the wavelength of the associated wave.

[h = 6.6 x 10-34 Js]

1.   Many candidates gave a fair attempt at this question as they found it very tractable.  However, few candidates were still using the word “spontaneous” in defining radioactivity.

1. Advantages of nuclear fusion over nuclear fission was poorly attempted.  However, they performed well in their attempt to state two methods of detecting radioactivity.
_____________________________________________________________________________________________________

• In the calculation of the energy released in the reaction, some candidates made themselves creditably equal to the required task.  However, few candidates found the conversion of the unified atomic mass to kilogram difficult.
• Very few candidates did the correct thing while most of other respondent candidates derailed by starting their responses on a wrong note; i.e with wrong formula.  Generally, performance was fair.

The expected responses are:

(a)(i)  Radioactivity is the decay/disintegration of the nucleus of an unstable
nucleus/atom (of an element) with the release of any one, two or all of
alpha, beta and gamma radiations.

(ii)    Types of radioactivity

• Natural and
• Artificial

(b)(i)   Advantages of nuclear fusion over nuclear fission

e.g
-           greater energy is released
-           less dangerous radiations are released
-           raw materials required are cheaper
-           raw materials are readily available.

(ii)    Methods of detecting radioactivity
Any correct 2
e.g
-           photographic films
-           Geiger muller (G-M) tube
-           (Electron) – e loud chamber
-           semiconductor detectors

(c)        m =   mass defect   =          (mass of products ) – (mass of reactants)

=          4.00150                                                          2.00141
+   1.00728                                  -                   +  3.00160
5.00878                                                          5.00301

Mass defect   =          0.00577u
=          5.77 x 10-3u
=          5.77 x 10-3 x 1.7 x 10-27 kg
=          9.81 x 10-30 kg
E         =          mc2
=          9.81 x 10-3 x ( 3 x 108 )2
=          8.83 x 10-13 J

(d)       λ          =          h
mV                                                                                                                             =                     6.6 x 10-34
9.1 x 10-31 x 4.8 x 108

=          1.51 x 10-12 m