Physics Paper 2, Nov/Dec. 2009

Physics Paper 2, Nov/Dec. 2011

Questions:	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	Main

General Comments
Weakness/Remedies
Strength

Question 15

(a) Can other elements besides uranium be used in nuclear fission reactions?
Give a reason for your answer

(b) A radioactive element has a half-life of 5 years. A detector placed near the element
records an initial count rate of 4000min-1 as stated in the table below.

t/years	0	5	10	15	20
Count rate/min	4000

           (i)     Copy and complete the table.
          (ii)     Plot a graph with count rate on the vertical axis and t on the horizontal axis.
         (iii)     Using the graph, determine the count rate at t = 12 years.
          (iv)    List two detectors of radioactive radiations

(c)

The diagram above illustrates the energy levels for a certain atom.
                (i)     Which of the transistions A,B and C produces radiation with the shortest
                       wavelength? Give a reason for your answer.
                (ii)     An electron jumps from Eo to E2 by absorbing light energy.
                          Calculate the wavelength of the light used.
                           [h = 6.6. x 10 -34 Js; c = 3.0 x 108 ms-1; IeV = 1.6. x 10 -19 J]

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comments

. This is not a popular question, most candidates could not profer correct reason why
uranium is not the only useable element for nuclear fission reaction.
Most candidates who attempted part (b) were able to complete the table correctly however, the plotting of the graph was poorly done as choice of scales was a problem. Few could not read-off the count rate at 12 years. Most candidates were able to mention Geiger – Muller counter as detector.

Part(c) this simple problem on energy quantization was poorly attempted some candidates could not achieve the necessary conversion and some made use of wrong formula.

The expected answer are:

. (a) Yes, Uranium is used because it is heavy and unstable. Elements with similar properties
can also be used.

b(i)

t/years	0	5	10	15	20
Connote rate min-1	4000	2000	1000	500	250

(ii)

                        Both axes distinguished
                        Reasonable scales (both axes)
                        Five points correctly plotted

                         Smooth curve

       (iii)     Count rate at 12 years
                     Correctly shown on graph
                     Correctly read
        (iv)    Suitable detectors
                  -    Scintillating detector
                  -    Geiger Muller Tube
                  -    Photographic films
                  -    Electron cloud chambers

C (i) Transition C

                This transition will produce the highest energy
           (ii)       E =
                  l =   =     6.6 x 10-34 x 3 x 108
                                        9.8 x 1.6 x 10-19
                                    =   1.3 x 10-7m