Physics Paper 2, May/June. 2012

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

General Comments
Weakness/Remedies
Strength

Question 15
(i) Explain why x-rays can be used to produce photographs of fractures in bones, List four uses of x-rays other than in medicine. State the energy transformations which takes place during the operation of an x-ray tube. (i) Explain three named dangers to which human beings may be exposed when subjected to large doses of x-rays. State two precautions that must be taken by persons working with x-rays. In an x-ray tube, an electron is accelerated from rest towards a tungsten target biased at a potential of 33 kV. Calculate, for the electron, the Kinetic energy; Velocity. [h = 6.6 x 10 34 jS; Me = 9.1 x 10 31 kg; c = 3.0 x 108 ms1; e = 1.6 x 10 19 C.
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comments
Part (a)(i) Many candidates wrote that it was because x-rays can penetrate flesh but are absorbed by bones. This is not the correct response to the question. The question was on fracture in bones (iii) Few candidates were still stating medical uses of x-rays. Performance Was fair. Part (b). This part was poorly rendered by most responding candidates Part (c) Many candidates were able to write out the dangers in the use of x rays but could not explain them The precautions was very easy for them to state. Part (d). This Is a numerical part. The formula, substitution and arithmetic was poorly done The expected answers are: (a) (I) X -rays cannot penetrate bones; but can pass through fractures. (it) Examination of bags, luggage at airport/sensitive places. Identification of chemical elements and their isotopes Detection of cracks in metallic products Detection of fake gems Detection of alterations which have been made to original works of art Electrical energy àHeat energy à kinetic energyàElectromagnetic energy à(X rays and Heat energy) (i) Cancer - destruction of living cells, tissues and organs. Leukemia - destruction of white blood cells Skin harms - tanning/burning of skin Cell mutation - change in cell genetic codes Precaution necessary while working with x-rays They should have routine medical checkups. They should wear lead/prospective coats. They should wear dosimeter. They should wear protective goggles (i) K.E = eV [1] = 1.6 x 10'l9x 33 x 103 = 5.28 x 1015J K.E = 1/2 mv2 5.28 x 10 15 = 1/2 x 9.1 x 10 31 x v2 v2 = 1 16 x 1016 v = 1.08 x ms-1